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SID 5 Research Project Final Report

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NoteIn line with the Freedom of Information Act 2000, Defra aims to place the results of its completed research projects in the public domain wherever possible. The SID 5 (Research Project Final Report) is designed to capture the information on the results and outputs of Defra-funded research in a format that is easily publishable through the Defra website. A SID 5 must be completed for all projects.

This form is in Word format and the boxes may be expanded or reduced, as appropriate.

ACCESS TO INFORMATIONThe information collected on this form will be stored electronically and may be sent to any part of Defra, or to individual researchers or organisations outside Defra for the purposes of reviewing the project. Defra may also disclose the information to any outside organisation acting as an agent authorised by Defra to process final research reports on its behalf. Defra intends to publish this form on its website, unless there are strong reasons not to, which fully comply with exemptions under the Environmental Information Regulations or the Freedom of Information Act 2000.Defra may be required to release information, including personal data and commercial information, on request under the Environmental Information Regulations or the Freedom of Information Act 2000. However, Defra will not permit any unwarranted breach of confidentiality or act in contravention of its obligations under the Data Protection Act 1998. Defra or its appointed agents may use the name, address or other details on your form to contact you in connection with occasional customer research aimed at improving the processes through which Defra works with its contractors.

Project identification

1. Defra Project code IF0153

2. Project title

A literature review of the effects of pesticides on micro-organisms during composting and of the degradation of 'biodegradable' plastic films and packaging during composting

3. Contractororganisation(s)

Warwick HRIUniversity of WarwickWellesbourneWarwickCV35 9EF

54. Total Defra project costs £ 30,993(agreed fixed price)

5. Project: start date................ 02 January 2008

end date................. 31 March 2008

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6. It is Defra’s intention to publish this form. Please confirm your agreement to do so...................................................................................YES NO (a) When preparing SID 5s contractors should bear in mind that Defra intends that they be made public. They

should be written in a clear and concise manner and represent a full account of the research project which someone not closely associated with the project can follow.Defra recognises that in a small minority of cases there may be information, such as intellectual property or commercially confidential data, used in or generated by the research project, which should not be disclosed. In these cases, such information should be detailed in a separate annex (not to be published) so that the SID 5 can be placed in the public domain. Where it is impossible to complete the Final Report without including references to any sensitive or confidential data, the information should be included and section (b) completed. NB: only in exceptional circumstances will Defra expect contractors to give a "No" answer.In all cases, reasons for withholding information must be fully in line with exemptions under the Environmental Information Regulations or the Freedom of Information Act 2000.

(b) If you have answered NO, please explain why the Final report should not be released into public domain

Executive Summary7. The executive summary must not exceed 2 sides in total of A4 and should be understandable to the

intelligent non-scientist. It should cover the main objectives, methods and findings of the research, together with any other significant events and options for new work.SCIENTIFIC OBJECTIVES

1. To review the literature on the effect of pesticides on microorganisms during composting.2. To review the literature on the degradation of ‘biodegradable’ films and packaging during composting.3. To review information on conditions in home and industrial scale composting systems in relation to (1) and (2).4. To consult with other relevant organisations, researchers and manufacturers to obtain information on (1), (2) and (3) above.5. To disseminate the results to the composting industry, compost end-users and research community and to make recommendations for future research and development.

Home composting has become an increasingly important method of organic waste disposal in the UK. About 40% of households with a garden have a home composting bin; ten and five years ago this figure was 25 and 32%. A WRAP initiative has resulted in an uptake of 1.7 M home composting bins. This is the only significant composting disposal route for plastic packaging waste that is designed to biodegrade in a composting environment, since it is not allowed in the green bin. The fate and influence of pesticides applied to plants and then in green wastes in composting has received much research attention. However, as with the development of biodegradable plastics, this research has nearly all been conducted in industrial composting systems or under controlled conditions in the laboratory. The conditions in large-scale and/or controlled composting systems are likely to differ significantly from those in home composting systems. The fate and influence of pesticides and plastics in home composting systems may therefore also differ markedly from those in industrial and/or controlled composting systems. This review was based on information obtained from 149 scientific papers, technical articles and test standards. Consultations were also held with relevant experts in the fields of biodegradable polymers and packaging and home composting systems.

CONCLUSIONS OF THE LITERATURE REVIEW AND CONSULTATIONS1. The composting environment within home systems differs from that in industrial-scale systems in terms of lower temperatures (particularly in winter), higher oxygen levels, and greater variability in waste feedstock degradation and mixing.

2. The predominant compost organisms responsible for degradation and their levels of activity differ between home scale and industrial scale systems. In large scale systems, mesophilic and thermophilic microorganisms are most important and are highly active; in small scale systems, mesophilic and

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psychrophilic microorganisms normally predominate at low levels of activity, and earthworm activity can also be significant.

Pesticides in Home Composting Systems3. The most likely source of pesticide contamination of waste feedstocks in home composting systems is

from residues of lawn-care herbicides on grass clippings from spring to late summer. The most widely used lawn-care herbicides are 2,4-D, mecoprop-P and MCPA. Dicamba, dichlorprop, chorpyralid and fluroxpyr are also used.

4. There has been little research on the direct effect of pesticides on compost organisms but the behaviour of a particular pesticide and its degradation in soil, which has been extensively researched, should be a reasonable approximation of what occurs during composting.

5. Thermophilic composting can enhance pesticide removal by microbial degradation and volatilisation. This is less likely to occur in home composting systems, and organic matter can increase the sorption and reduce the microbial availability of some pesticides. However, composts generally enhance the degradation of pesticides over that obtained in soil, even at ambient temperatures.

6. The most toxic and recalcitrant pesticides during composting are OCs and the OP diazinon, but these are no longer approved for use. The majority of OP and carbamate insecticides and herbicides are less toxic to compost organisms and degrade readily.

7. Herbicides are generally less toxic to soil microbes and earthworms (and therefore probably less toxic to compost organisms) than insecticides and fungicides.

8. Based on typical patterns of use, toxicity and degradation, the risk posed by pesticides to the composting process in home systems and to the end use of the compost is very small.

Biodegradable packaging and films in Home Composting Systems 9. Most of the experiments and testing standards on the compostability of plastics have been conducted

at optimum temperatures for their biodegradation of 52-65˚C. There is no published information on the composting of plastics/polymers in small-scale home composting bins that typically operate at close to ambient temperatures.

10. AIB-Vinçotte International has developed an OK Compost Home logo for materials that will compost under conditions aimed to simulate some of those found in home composting bins, i.e. materials that show at least 90% degradation at ambient temperature (20oC) in 180 days. However, there are significant differences between these ‘simulated’ conditions and those that actually occur in real home composting bins.

11. Very few products have met the requirements of OK Compost Home, e.g. films and plastic bags made from Novamont’s Mater-Bi.

12. Previous research on the compostability of plastics has been conducted using a diverse range of plastic inclusion rates and composting conditions (wastes, moisture content, aeration). These factors are likely to have significant effects on the rate of biodegradation of plastics and the variability makes it difficult to compare results obtained from different researchers and/or with different materials.

13. There is some evidence that compostable plastics biodegrade more rapidly in the presence of earthworms, by ingestion and/or by enhanced degradation in vermicomposts.

14. Previous studies on the ecotoxicity of oxo-degradable plastics (widely used in carrier bags) have generally been conducted at low inclusion rates. There is a lack of information on effect of high inclusion rates of these materials, in soil and in compost, on the growth of microorganisms, fauna and plants over time.

RECOMMENDATIONS FOR FUTURE RESEARCH

These recommendations are aimed at maximising the amount of compostable plastic packaging that can be composted in home composting systems, and diverting waste from landfill where it will generate methane under anaerobic conditions.1. The compostability of biodegradable plastics needs to be tested in actual home composting systems

and comparisons made with degradation under ‘optimum conditions’.2. In the research, the effects of typical temperatures and feedstocks, composting durations and gradual

filling of home composting systems on the rate of composting of plastics should be examined. 3. The proportion of compostable plastic that can be mixed with other organic wastes without adversely

affecting the composting process or the final quality of the compost needs to be determined.4. The inter-relationship between compostable plastics, microorganisms and earthworms should be

investigated further in home composting systems.5. More information is needed on the ecotoxicity of oxo-degradable plastics in composts and soils,

particularly the effect on microorganisms, fauna and plants.

Project Report to Defra

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8. As a guide this report should be no longer than 20 sides of A4. This report is to provide Defra with details of the outputs of the research project for internal purposes; to meet the terms of the contract; and to allow Defra to publish details of the outputs to meet Environmental Information Regulation or Freedom of Information obligations. This short report to Defra does not preclude contractors from also seeking to publish a full, formal scientific report/paper in an appropriate scientific or other journal/publication. Indeed, Defra actively encourages such publications as part of the contract terms. The report to Defra should include: the scientific objectives as set out in the contract; the extent to which the objectives set out in the contract have been met; details of methods used and the results obtained, including statistical analysis (if appropriate); a discussion of the results and their reliability; the main implications of the findings; possible future work; and any action resulting from the research (e.g. IP, Knowledge Transfer).

SCIENTIFIC OBJECTIVES

(1) To review the literature on the effect of pesticides on micro-organisms during composting.

(2) To review the literature on the degradation of ‘biodegradable’ films and packaging during composting.

(3) To review information on conditions in home and industrial scale composting systems in relation to (1) and (2).

(4) To consult with other relevant organisations, researchers and manufacturers to obtain information on (1), (2) and (3) above.

(5) To disseminate the results to the composting industry, compost end-users and research community and to make recommendations for future research and development.

These objectives have been met in full.

Abbreviations and acronyms used in this report are explained in the Appendix.

1. INTRODUCTION

Home composting has become an increasingly important method of organic waste disposal in the UK. About 40% of households with a garden have a home composting bin; ten and five years ago this figure was 25 and 32% (M. Lennartsson pers. comm.). A WRAP initiative on home composting has resulted in an uptake of 1.7 M composting bins.

The fate and influence of pesticides applied to plants and then in green wastes in composting has received much research attention. There has also been a large amount of research and commercial development of plastics that are designed to biodegrade in a composting environment. However, this research has nearly all been conducted in industrial composting systems or under controlled conditions in the laboratory. The conditions in large-scale and/or controlled composting systems are likely to differ significantly from those in home composting systems. The fate and influence of pesticides and plastics in home composting systems may therefore also differ markedly from those in industrial and/or controlled composting systems.

2. CONDITIONS IN INDUSTRIAL SCALE AND HOME COMPOSTING SYSTEMS

2.1 Factors Affecting the Composting ProcessComposting is a complex biological process through which a wide range of microorganisms metabolise organic materials (wastes feedstocks) into compost. It is mainly an aerobic process by which microorganisms consume oxygen to extract energy and nutrients from organic matter. In doing so, they produce heat, water, compost, CO2 and other gaseous by-products (Day & Shaw 2001). Composting can occur under a wide range of conditions, but the process occurs more rapidly if a number of conditions are optimised (Day & Shaw 2001; Rynk & Richard 2001) (Table A1, Appendix). Composting will still occur under conditions outside of the ‘reasonable range’ but the process will become progressively slower.

Based on microbial activity and compost temperatures, the composting process can be divided into a series of different stages:(a) psychrophilic stage (0 – 20°C); microbial activity is very low or latent(b) mesophilic stage (20 – 45°C) where mesophilic bacteria predominate

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(c) thermophilic phase (>45°C) during which thermophilic bacteria, as well as fungi and actinomycetes predominate; nutrients gradually become depleted(d) second mesophilic phase (<45°C), microbial activity gradually declines(e) final maturation phase, temperatures near to ambient.

As well as changes in temperatures, the other parameters also change as the composting process progresses (Table A1, Appendix). The carbon:nitrogen (C:N) ratio usually decreases from about 25:1 to 14:1 as C is lost as CO2. The O2 concentration will decrease as the compost temperature and CO2 evolution increase. Subsequently, as the rate of composting decreases, the O2 level should gradually increase. There is usually a decrease in moisture content through water vaporisation, unless water is added or compost temperatures are inadequate and the compost is not protected from precipitation. The compost becomes more compacted as the particle size reduces. During the early stages of composting, the pH usually falls due to production of organic acids. As composting proceeds, the pH becomes neutral again as these acids are converted to methane and CO2. The pH of the final material is usually slightly alkaline.

2.2 Micro-organisms Involved in CompostingThe microorganisms that are mainly responsible for the composting process are bacteria, fungi and actinomycetes. The populations and microbial diversity of these different types of microorganisms change during the composting process (Day & Shaw 2001). Microbial populations have been monitored using both traditional plate culture techniques as well as analysis of phospholipid fatty acid (PLFA) patterns and molecular approaches (16S rDNA analyses) (Ryckeboer et al. 2003).

2.2.1 BacteriaBacteria are usually present in large numbers throughout the whole composting period and are the main microbial species responsible for the degradation processes. They are about 100 times more prevalent than fungi (Day & Shaw 2001). The actual bacterial species are dependent on the feedstock wastes and the compost conditions. During the mesophilic phases, bacteria belonging to genera such as Bacillus, Pseudomonas and Arthrobacter predominate. These are replaced by thermophilic bacteria such as other Bacillus species during the thermophilic phase (Strom 1985).

2.2.2 ActinomycetesActinomycetes are not usually present in appreciable numbers until the composting process is well established. They may then be readily detected by their greyish appearance spreading through the compost pile (Day & Shaw 2001). Actinomycetes that are regularly found in compost are species of the genera Micromonospora, Streptomyces and Actinomyces. They can utilise a wide range of substrates and are important in the degradation of the cellulosic component of waste, as well as some of the lignin (Day & Shaw 2001).

2.2.3 FungiFungi appear in compost at a similar time to the actinomycetes. Two main forms occur – moulds and yeasts. The species diversity in compost is much greater than for bacteria and actinomycetes. Mesophilic species occur below 45°C and thermophilic fungi are active up to 60°C, above which only a few fungi survive (e.g. Aspergillus fumigatus) (Strom 1985). Common cellulose degrading fungi include Aspergillus, Penicillium, Fusarium, Trichoderma and Chaetomium species. White rot fungi (Basidiomycetes) are important in the degradation of lignin (Day & Shaw 2001).

2.2.4 EarthwormsDegradation of organic matter by earthworms is of relatively minor importance in large-scale composting systems due to the high compost temperatures (unless they are deliberately introduced into systems kept at lower temperatures as in vermicomposting). The optimum temperature for earthworm activity is 15 – 25°C; they are killed at temperatures above 35°C (Gilbert et al. 2001). However, in some small-scale composting systems and in vermicomposting, their degradative activity is of greater importance (Smith et al. 2004). Removal of earthworms and microarthropods by fumigation reduced the breakdown of leaf litter by 25% (Brown 1978). The most important species for vermicomposting are Dendrobaena veneta, brandlings (Eisenia fetida) and Eisenia andrei.

2.2.5 EnzymesThe utilisation of enzymes is an essential component in the degradation activity of all compost microorganisms. Enzymes are proteins that lower the activation energy for a reaction resulting in an increase in the rate of the reaction. Similar factors to those that influence microbial activity (e.g. temperature, chemical environment) have an effect on enzyme activity and a change in any one parameter can inactivate the enzyme or destroy it.

2.2.6 Measuring microbial activity in compostIn almost all scientific studies of the composting process, temperature-time relationships are usually presented to represent the rate of microbial activity with time (Day & Shaw 2001). Composting is essentially an oxidationprocess where O2 is consumed and CO2 is produced. Consequently monitoring these two gases during the composting process can provide a reliable indication of composting activity. The evolution of various other volatile gases such as ammonia and organic acids can also be indicative of the activity or stability of the compost. During

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the composting process, the ash or inorganic component increases due to the loss of the organic fraction or volatile solids as CO2. Consequently, the measurement of ash content is a crude indicator of the extent of composting. However, the measurement of ash content alone tends to lack sensitivity due to its dependence upon sampling practices. Losses in volatile solids are very much dependent on the feedstocks used, with values ranging from 17 to 53% (Day & Shaw 2001). Fluorescein diacetate (FDA) is a nonfluorescent substrate that is hydrolysed by various enzymes (mainly esterase but also proteases and lipases) found in living cells to yield fluorescein which can be quantified by spectrophotometry. This has been used to measure microbial activity in composts (Ryckeboer et al. 2003).

2.3 Composting SystemsThe predominant feedstock wastes in both large industrial scale systems and home composting are green garden waste (woody and soft plant material) and food or kitchen wastes. The proportions of these feedstocks will change according to season, locality (urban or rural) and between individual composting sites or households. Industrial composting sites may also include feedstocks such as paper pulps, animal wastes, sewage sludge, sawdust and straw.

2.3.1 Industrial scaleIndustrial scale composting systems differ in terms of how aeration occurs: passive aeration, which usually includes periodic turning, and forced aeration, where air is supplied mechanically via fans (Rynk & Richard 2001). Within each of these two main groups of composting systems, there are a range of specific types of system. In passive systems, materials are usually composted in open freestanding piles or windrows. The systems may be housed within a building, but the composting environment is otherwise not controlled, other than by periodic turning. In-vessel or enclosed composting systems usually employ forced aeration and/or some means of agitation. Composts in large-scale systems are usually prepared in a batch process with no new material being added once a batch starts to compost. The organic material in a batch is therefore at a similar level of degradation.

Composts in large-scale systems usually reach temperatures in excess of 55°C for more than 7 days, and this a requirement if the compost is to meet the standard of Publicly Available Specification 100 (PAS 100:2005). Christensen et al. (2002) monitored the temperatures in 16 large-scale facilities (windrow, in-vessel and revolving drum facilities). The maximum temperature exceeded 60°C in 13 of the facilities and 50°C in the other three. The duration of composting varied from 2 to 18 months. Feedstocks may be mechanically pre-treated such as shredded before composting and wastes (e.g. food and green wastes) may be mixed to improve the compost formulation.

2.3.2 Home compostingAbout 40% of homes with a garden have a composting bin; 10 and 5 years ago the figures were 25 and 32% (M. Lennartsson pers. comm.). Home composting is typically conducted in systems of less than 1 m3. The heaps may be enclosed in some form of wooden frame or conducted in purpose-built plastic vessels, usually with a volume of less than 300 L. Nearly 70% of the bins are the 220 L and 330L plastic Compost Converters (Blackwell, Leeds) (M. Lennartsson pers. comm.). About 1.7 M bins have been distributed as part of the WRAP home composting initiative. Frequent inputs of waste mean that waste is present at different levels of decomposition. In a WRAP survey of about 100 home composting bins; 82% contained mixed food and garden waste and 18% contained only garden waste (P. Skelton pers. comm.). Typically, kitchen waste would be added at daily to weekly intervals, whereas garden waste would be added at weekly to monthly intervals.

Measurements with green garden waste showed that the temperature did not exceed 30°C over a one year period, although periodic turning and larger bin size (790 L instead of 280 L) increased compost temperatures slightly (Alexander 2007). In 290 L bins containing mixed kitchen and garden waste, temperatures generally remained within the range 10 – 40°C although temperatures within the range 45 – 70°C were recorded in a small proportion of bins (Smith et al. 2004). There was a strong seasonal effect, with compost temperatures between December and February not reaching 20°C in the majority of bins. O2 concentration in the bins did not fall below 16 % v/v. The majority of home composting bins are not turned (M. Lennartsson pers. comm.). Typical composting durations are 12 – 18 months. Earthworm activity can be significant in home composting, particularly if wetter food wastes are included. The main differences between large-scale industrial composting systems and home composting are summarised in Table A2 (Appendix).

3. EFFECT OF PESTICIDES ON THE COMPOSTING PROCESS

3.1 Levels of Pesticide in Compost FeedstocksComposts may become polluted by organic pollutants through accidental aerial deposition or through deliberate application of pesticides (Brändli et al. 2005). Based on the relative amounts applied, herbicides as a group are more likely to be present in composting feedstocks from urban or agricultural uses, compared with insecticides or fungicides (Buyuksonmez et al. 1999). The most commonly used residential lawn-care herbicide is 2,4-D (Michel et al., 1995). Mecoprop-P, mecoprop, MCPA, chlorpyralid, dicamba, fluroxypyr and dichlorprop are also widely used for lawn application. Glyphosate is widely used as a garden herbicide but is less likely to enter compost

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feedstocks than lawn care products. Brändli et al. (2005) reviewed the concentration of persistent organic pollutants in compost and its

feedstock materials. The concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins and –furans (PCDD/Fs) were higher in green waste (foliage) than in organic household waste or kitchen waste. Investigations of pesticide residues in composting feedstocks and finished compost detected few of the target pesticides (Buyuksonmez et al. 1999). The majority of compounds detected were insecticides in the organochlorine (OC) category which have been banned from use for several years. Organophosphate (OP) and carbamate insecticides were rarely detected. Strom (2000) reports on analyses of green wastes for pesticides and PCBs. The OC insecticide chlordane was found in almost all the samples tested and 21 other pesticides were found at low or very low levels in at least one sample. Strom (2000) also noted that the majority of pesticides now in use, including lawn care products, are readily biodegradable and the low levels initially present are expected to decrease during composting. Wilson et al. (2003) assessed green wastes for the presence of 38 herbicides, eight insecticides and two fungicides. Of the pesticides monitored, only the OC insecticides chlordane, 4,4-DDE and endosulfan, and the herbicide atrazine, were detected. In Washington State, composted materials were found to cause tomato damage. Testing of materials used to make compost identified two herbicides: clopyralid in lawn-clippings and picloram in bedding and manure (Rynk 2000).

It is unlikely that garden waste in home composting systems will have been recently sprayed with pesticides, since pruning does not usually coincide with spraying, and there is usually a recommended delay between applying lawn-care products and mowing (P. Alexander, pers. comm.). Brändli et al. (2005) found that the concentrations of persistent organic pollutants in green wastes were higher during the spring. Herbicide treated lawn-clippings are most likely to be introduced into compost in early and late summer (Rynk 2000).

3.2 Effect of Pesticides on MicroorganismsThere has been a significant amount of research on the effect of pesticides on soil microorganisms since this information is required for the registration of new chemicals (Somerville & Greaves 1987; Johnsen et al. 2001). There has been much less research on the effect of pesticides on microorganisms in compost or on the composting process. The behaviour of a particular pesticide in the soil should be a reasonable approximation of what might occur during composting although compared with a soil environment, composting can enhance or hinder pesticide degradation, depending on the composting method and nature of the pesticide (Buyuksonmez et al. 1999). The effect of pesticides on soil microorganisms has been examined by determining the influence on soil respiration (CO2 evolution; FDA hydrolysis) and N-turnover (Jonk & Barug 1987; Johnen & Drew 1977; Bünemann et al. 2006). Several hundred papers on the effects of pesticides on microorganisms in soil have not revealed any long-term harmful effects on numbers, composition, and activities of the microflora, at least at normal rates of application (Johnen & Drew 1977; Bünemann et al. 2006). Fairly high concentrations, above 1000 mg kg-1 soil, of pentachlorphenol, 2,4,4-T or carbendazim, were required to reduce soil respiration below that of untreated soil (Vonk & Barug 1987). However, the bacterial community structure in soil may be markedly changed even if the overall nitrogen and carbon metabolism appears unaffected by a pesticide (Johnsen et al. 2001).

3.2.1 Herbicide effects on microorganismsHerbicides are generally less toxic to soil microorganisms than insecticides and fungicides (Simon-Sylvestre & Fournier 1979; Buyuksonmez et al. 1999; Bünemann et al. 2006). Compounds applied to soil as selective herbicides have caused either no change in the total microbial community, or a reduction that is transitory. Often the initial reduction is followed by a net increase in microorganisms, as genotypes become prevalent that break down the herbicides (Brown 1978). This includes phenoxy acids (e.g. 2,4-D), triazines (e.g. atrazine), urea compounds (e.g. diuron), selective organics (e.g. picloram) and nonselective organics (e.g. TCA). Paraquat has been shown to cause a short term reduction in the bacterial and fungal population of soil, and carbamates (e.g. propham) and the sulfonylurea herbicide prosulfuron caused a temporary inhibition of nitrifying bacteria such as Azotobacter (Brown 1978; Kinney et al. 2005). Malkomes (1987) found that although the short-term soil respiration was inhibited by the application of several herbicides (propham, medinobacetate, TCA, cycloate), respiration over the long-term (more than 1 week) was stimulated. Ou et al. (1978) found that high concentrations of 2,4-D stimulated CO2 evolution from some soils.

Herbicides such as trifluran, atrazine and simazine generally modify soil fungal populations (Simon-Sylvestre & Fournier 1979). Seghers et al. (2003) showed that the long-term use of the herbicides atrazine andmetolachlor resulted in an altered soil community structure, in particular for the methanotrophic bacteria, even though the overall methane oxidation of the soil remained unchanged. Perucci et al. (2000) found that application of the sulfonylurea herbicide, rimsulfuron, and the imidazolinone herbicide, imazethapyr, had a detrimental effect on soil microbial biomass only when applied at 10-fold field rates; a similar effect of dinoseb application was reported by Simon-Sylvestre & Fournier (1979). The detrimental effect of herbicide application on soil respiration was reduced by amending the soil with organic compost (Perucci et al. 2000)

3.2.2 Insecticide effects on microorganismsInsecticides have generally little or no effect on the soil populations of microorganisms when applied at normal rates, except for some OC compounds, which are no longer approved for use in the UK (Simon-Sylvestre & Fournier 1979; Bünemann et al. 2006). None of five OC compounds (DDT, BHC, aldrin, dieldrin, chlordane) or

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two OP compounds (EPN and parathion) applied at a rate of 11.2 kg ha-1 to soil had any significant negative effect on the total numbers of bacteria, actinomycetes and fungi (Bollen et al.1954). Even at a higher concentration, equivalent to an application of 112 kg ha-1, no deleterious effects of these compounds were found on the total numbers of soil microorganisms (Brown 1978). Chlorpyriphos and quinalphos reduced bacterial numbers but increased fungal numbers in soil (Simon-Sylvestre & Fournier 1979).

3.2.3 Fungicide effects on microorganismsSoil bacterial populations have been shown to be resistant or even stimulated by a number of fungicides including dithiocarbamates (e.g. thiram), benomyl and OCs (e.g. PCNB) (Brown 1978; Simon-Sylvestre & Fournier 1979). Captan, benomyl and copper-based fungicides have all been shown to reduce soil respiration (Simon-Sylvestre & Fournier 1979). Fungicide applications to soil change the fungal species composition from susceptible groups such as Phycomycetes to more resistant genera such as Aspergillus and Trichoderma (Brown 1978). However, the changes caused by fungicides, other than by persistent copper-based fungicides, are likely to be only temporary (Simon-Sylvestre & Fournier 1979)

3.3 Effect of Pesticides on EarthwormsAs with microorganisms, the research on the effect of pesticides on earthworms has usually been conducted in a soil environment. As well as Eisenia species which are of importance in composting, much of this research has been conducted on Allolobophora, Drawida and Lumbricus species (Brown 1978; Bünemann et al. 2006).

3.3.1 Herbicide effects on earthwormsHerbicides are generally less toxic to earthworms than insecticides or fungicides (Bünemann et al. 2006; J. Frederickson pers. comm.). Some herbicides (TCA, simazine, chlorpropham) are directly toxic to earthworms while others (2,4-D and paraquat) are harmless at normal application rates (Brown 1978).

3.3.2 Insecticide effects on earthwormsVery lipophilic, persistent pesticides such as OCs can potentially be transferred from compost to soil-dwelling organisms such as earthworms which ingest composted materials (Wilson et al. 2003). Several OC compounds such as chlordane and toxaphene are toxic to earthworms when applied to soil at a rate of about 2.5 kg ha -1 (Brown 1978). Carbamate insecticides such as carbofuran are also toxic to earthworms (Bünemann et al. 2006). Several OP compounds examined (thionazin, chlorfenvinphos, diazinon, trichlorfon, disulfoton, dimethoate) had little lasting effect on earthworm populations, although phorate and fensulfothion caused heavy initial kills and malathion reduced reproduction. (Brown 1978; Bünemann et al. 2006). There is little evidence that OP insecticides can be concentrated by earthworms in their tissues (Brown 1978). Diazinon was found to be toxic to Eisenia earthworms but composting diazinon-containing wastes for 60 days at 60°C resulted in hydrolysis and loss of toxicity (Leland et al. 2003).

3.3.3 Fungicide effects on earthwormsFungicides are generally more toxic to earthworms than herbicides or insecticides (J. Frederickson pers. comm.). Copper-based fungicides caused long-term reductions in earthworms (Bünemann et al. 2006). Benzimidazole fungicides (benomyl and carbendazim) are also toxic to earthworms (Brown 1978; Kinney et al. 2005; Bünemann et al. 2006).

3.4 Pesticide Degradation during CompostingThere has been a large amount of research on the degradation of pesticides during composting. This has a direct influence on the likely impact of pesticides on compost microorganisms and the composting process, since the faster pesticides are removed, the less likely they are to exert a toxic effect. An estimate of the persistence of a pesticide is its half-life (DT50) – the time taken for the chemical to degrade to half of its initial concentration (normally in soil). The time taken for a pesticide to practically disappear can be several half-lives (Rynk 2000).

There are a number of possible routes of removal of pesticides from compost, including complete biodegradation, transformation into other compounds, assimilation into microbial biomass, volatilisation, leaching and sorption (Fogarty & Tuovinen 1991). Because composting normally involves vigorous biological activity, it canbe expected to accelerate the decomposition of pesticides that takes place in the soil (Buyuksonmez et al. 1999). Compost amendment of soil contaminated by certain pesticides has also resulted in an increase in pesticide degradation (Cole et al. 1995). This indicates that for some pesticides, degradation occurs more rapidly in compost than in soil, even at ambient temperatures. However, certain organic pesticides do not readily decompose and may pass through a composting process with little change, or partially degrade into secondary toxic compounds (Buyuksonmez et al. 1999). If the compost contains rapidly degradable material such as grass clippings, the concentration of recalcitrant pesticides can increase (Rynk 2000). The stabilised fraction of organic wastes can lower pesticide degradation by adsorption processes (Perucci et al. 2000; Said-Pullicino et al. 2004). There are several examples of pesticide degradation in compost being increased, decreased or unaffected compared with degradation in soil (Briceno et al., 2007)

Volatilisation of pesticides can be a particularly important removal mechanism for a number of pesticides due to the high temperatures plus the forced aeration and agitation that takes place during composting (Buyuksonmez et al. 1999). However, these features of composting are much less pronounced or absent in home

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composting systems compared with industrial scale systems. Vandervoort et al. (1997) found that five pesticides, chlorpyrifos, 2,4-D, flurprimdol, isoxaben and triclopyr, degraded more rapidly inside heaps of grass clippings than on the outside. However, all the pesticides had degraded to less than 2% of the initial concentration after 1 year.

3.4.1 Herbicide degradationMany herbicides are not persistent and decompose readily during composting, although paraquat has a very long half-life (500 days) (Buyuksonmez et al. 1999). Rynk (2000) reported on two cases of herbicide damage to tomato plants resulting from clopyralid and picloram passing though windrow composting systems for 60 – 90 days. Lemmon & Pylypiw (1992) found no detectable levels of chlorpyralid or pendimethalin after 17 weeks of composting treated grass clippings in a bin at 27-52°C. The UK Pesticide Guide (Whitehead 2008) recommends that grass clippings that have been treated with mecoprop-P or MCPA should be composted for at least six months before use as a mulch on plants although no data for this recommendation are provided.Michel et al. (1995;1996) found that although a large proportion of 2,4-D completely degraded during composting at 50-70°C, the majority of pendimethalin was adsorbed on to humic substances in the compost and became unextractable. Parker and Doxtader (1982) found that at low concentrations, soil microorganisms were able to utilise and degrade 2,4-D, whereas at high concentrations, degradation was inhibited.

Atrazine completely disappeared after 160 days of composting but only 11% was mineralised to CO2 (Rao et al., 1995;1996). The degradation of atrazine was affected by the compost substrate but there was no effect of compost temperature in the range 25-55°C. Judge et al. (2000) found that less than 0.5% of the herbicide atrazine and the insecticide chlorpyrifos was mineralised into CO2 during composting at 40°C; the majority of the pesticides was sorbed by the organic components of the compost. In experiments of Getanga (2003) and Getanga & Kengara (2004), compost amendment of soil increased degradation and mineralisation of atrazine but not of glyphosate

Degradation of the herbicides trifluralin, metachlor and pendimethalin occurred more rapidly in 50:50 soil:compost mixes than in soil alone (Cole et al. 1995). Amendment of soil with spent mushroom compost increased the degradation of atrazine (Kadian et al. 2007). However, amendment of soil with compost reduced the rate of degradation of the herbicide triasulfuron compared with nonamended soil, due to adsorption of the herbicide to the organic matter and reduced availability to microorganisms (Said-Pullicino et al. 2004). Barriuso et al. (1997) also found that the degradation of highly-sorbed herbicides (atrazine, simazine, terbutryn, pendimethalin and dimefuron) was reduced by compost amendment of soil. Compost addition to soil had little effect on the less sorbed herbicides (carbetamide, 2,4-D and metsulfuron-methyl). Cox et al. (2001) found that amendment of soil with organic matter increased both the sorption and degradation of simazine and 2,4-D compared with nonamended soil. Moorman et al. (2001) found no effect of compost amendment of soil on the degradation of atrazine, matachlor and trifluralin.

The DT50 values in soil of the commonly used lawn-care herbicides 2,4-D, mecoprop-P and MCPA are all less than 14 days (Tomlin 2006) so persistence in compost would not be expected.

3.4.2 Insecticide degradationOC insecticides are the most resistant to decomposition during composting whereas the majority of OP and carbamate pesticides decompose readily during composting (Buyuksonmez et al. 1999). Brown et al. (1997) found that the OC insecticide lindane degraded very slowly in a 200 L barrel composting system which was turned weekly although Frenich et al. (2005) reported more rapid degradation of lindane in compost at 33-48°C. The OC insecticide endosulphan degraded more slowly under the same composting conditions. Petruska et al. (1985) found that about 50% of chlordane and 22% of the OP diazinon was lost from compost held at 65°C for 3 weeks through volatilisation, and less than 1% was mineralised. Neither of these insecticides is approved for use in the UK. Michel et al. (1996;1997) and Leland et al. (2003) found that diazinon readily broke down into a water soluble but less toxic product (IMHP) and only 11% or less was completely degraded into CO2 after composting at 55-60°C for 54-60 days. Two other OP insecticides, EPN and fenitrothion, degraded within 50 days of composting in food waste at an average temperature of 24°C, whereas 81% of diazinon degraded under the same conditions (Kawata et al. 2006).There were no detectable levels of the diazinon or isofenphos in treated grass clippings after 17 weeks in a composting bin at 27-52°C (Lemmon & Pylypiw 1992).

3.4.3 Fungicide degradation Captan degraded fairly rapidly in the barrel composting system of Brown et al. (1997) previously described. Neither captan nor lindane were lost by volatilisation or leaching and both pesticides were rapidly adsorbed to the compost matrix where they were biodegraded.

4. DEGRADATION OF BIODEGRADABLE FILMS AND PACKAGING DURING COMPOSTING

4.1 IntroductionAbout 1.5 M tonnes of household plastic packaging is produced annually in the UK, divided about equally between bottles, trays/punnets and films/bags. Currently, about 31% of packaging is recycled out of 75% that is easily recyclable. Only 5-10,000 tonnes of biodegradable plastic packaging is used, the majority for organic fruit and vegetables (P. Skelton pers. comm.). Between 200 and 300 packaging products have been certified as biodegradable (A. Campbell pers. comm.). The main growth area is in use in films and plastic bags.

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Composting and biogasification (anaerobic digestion) are two methods used for recycling of biodegradable plastics. These materials may also be used for energy recovery through incineration, although composting is the preferred method for dealing with these materials post-consumer as incineration produces a lower calorific value than for oil-based plastics, e.g. starch 14.5-16.5 MJ kg-1; polyethylene 44.8 MJ kg-1 (Davis & Song 2006) and landfill is not suitable for disposal of organic materials due to the negative environmental effects of methane production (Landfill Directive (1999/31/EC)).

In the UK, there is currently no infrastructure for collection and composting of biodegradable packaging at industrial composting sites (Skelton 2008). This waste can not be put into the green waste recycling bins provided by local councils, although this can be done with biodegradable plastic bags in the Netherlands (Platt 2006). In addition, should a kerbside collection of these wastes with green waste be introduced, there are concerns amongst compost producers regarding contamination of the waste stream with non-compostable packaging, and how much compostable packaging can be disposed of in the feedstock without reducing the quality of the final compost (E. Nichols pers. comm.). In the UK therefore, the only composting route for disposal of biodegradable packaging waste is via home composting. The standards for biodegradation of packaging usually relate to conditions found in industrial-scale composting systems. As outlined in Section 1, compost temperature and other conditions differ significantly between industrial-scale and home composting systems. Packaging compliant with EN 13432 will not necessarily degrade in home composting bins. Therefore, for biodegradable packaging to be disposed of via composting, the packaging needs to be home compostable. Currently, only a small proportion of compostable packaging is put into the home composting bin, the majority is disposed of in landfill. Some composters and anaerobic digester facilities accept biodegradable plastic packaging, mainly from ‘closed loop’ sources, such as waste from caterers where there is no contamination with non-degradable plastics (E. Nichols pers. comm.; P. Skelton pers. comm.).

4.2 DefinitionsBiodegradable plastic/polymer. Degradation results from the action of naturally occurring microorganisms such as bacteria, fungi and algae (ASTM D 6002 - 96). The material is completely assimilated (utilised) by the microorganisms present in the disposal system as food for their energy and enters into the microbial food chain (Anon. 2006). “Biodegradable” does not imply any particular time scale in the degradation process or that the material is compostable.Compostable plastic/polymer. These materials will biodegrade in an industrial composting environment in less than 180 days, producing CO2, water, inorganic compounds and biomass at a rate consistent with known compostable materials (Swift 1992). Industrial compost environment means a defined temperature of about 60oC, a defined moisture level (c. 50%) and microorganisms must be present. The material must biodegrade to mineral end products and biomass, disintegrate into invisible particles and have no negative effect on compost quality. Compostable plastics according to this definition do not leave fragments which persist longer than approximately 12 weeks in the residue, they do not contain heavy metals or toxins and the end product will support plant life (Anon. 2006).Home compostable. A material suitable for composting in a compost bin, compost heap or compost trough and in ideal situations the material will break down within 16 weeks at a temperature of 20°C (Anon. 2005).Degradable plastic/polymer. A material designed to undergo a significant change in its chemical structure under specific environmental conditions, resulting in a loss of some properties that may be measured by standard methods appropriate to the plastic and the application in a period of time that determines its classification (ASTM D 6002 - 96). This includes both plastics that degrade by physical or biological factors (sunlight or heat, or microbial action) although the products may not be usable by living organisms as food or energy. This type of degradation results in small fragments that pollute compost, landfill or the marine environment (Anon. 2006).(a) oxo-degradable - undergo degradation accelerated by catalysts or additives at elevated temperatures.(b) photo-degradable - undergo degradation by light.Synthetic polymer. A polymer not found in nature but produced artificially e.g. from fossil-origin-based monomers. Biopolymer. A polymer derived from biomass, produced by living organisms. This definition has been broadened to include materials produced or derived from these natural polymers (Davis & Song 2006). They may be (a) natural polymers, such as cellulose, starch, proteins and DNA in which the monomer units are sugars, amino acids and nucleic acids respectively; (b) synthetic polymers made from biomass monomers, e.g. polylactic acid (PLA), polyhydroxyalkanoates (PHA); or (c) synthetic polymers made from synthetic monomers derived from biomass (e.g. polyethylene derived bioethanol) (Anon. 2007a).Biodegradable biopolymer. A renewable polymer produced in nature by all living organisms. They include polysaccharides such as cellulose and starch and aliphatic polyesters such as PHA (Platt 2006).Synthetic biodegradable polymer. A synthetic polymer which either naturally exhibits a level of biodegradability, e.g. polycaprolactone (PCL) and poly (vinyl alcohol), or has been chemically modified to facilitate biodegradation (Davis & Song 2006). They may or may not be renewable depending on the monomer used for their production (e.g. PLA; oil-based PCL) (Platt 2006). Degradation may be activated by microbial action, hydrolytically or oxidatively via susceptible linkages built into the backbone of the polymer, or through additives that catalyse breakdown of the polymer chains. The stimulus to degradation may be designed to ensure the product serves its useful life but will disintegrate once this purpose has been served (David & Song 2006).Modified biodegradable biopolymer. A material produced from the combination of biodegradable biopolymers with synthetic polymers (Platt 2006).

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4.3 Biodegradable PolymersBiodegradable biopolymers used commercially in films and packaging are summarised in Table A3 (Appendix).

4.3.1 Biodegradable biopolymers(a) PolysaccharidesThe main polysaccharides currently used in the packaging industry are cellulose and starch (Chandra & Rustigi 1998). To overcome its infusibility and broaden its application, cellulose is usually converted into derivatives such as esters e.g. cellulose acetate, prior to use (Rhim & Ng 2007).

Starch is an inexpensive biopolymer that is readily available from agriculture. However, in its raw state, starch is unsuitable as an ingredient of biodegradable packaging (film) as it exhibits no plasticity, thermally degrades at around 260oC and is lacking in suitable mechanical properties (Fang et al. 2005). The properties of starch can however be improved for this application by combining starch in an extruder with plasticizers such as water or glycerol to produce a material that is thermoplastic and mouldable (Fang et al. 2005). One drawback to the use of starch in packaging applications is its potential to react with water in the environment and biodegrade prior to the end of its intended life.(b) Polyhydroxyalkanoates (PHAs)The use of PHAs in the production of biodegradable materials has been limited due to high production costs, limited availability and failure to meet the requirements of applications which currently use conventional plastics (Philip et al. 2007).

4.3.2 Synthetic biodegradable polymers(a) Polylactic Acid (PLA)PLA is a linear thermoplastic polyester produced by the polymerisation of lactide. Lactide is produced by the controlled depolymerisation of lactic acid obtained from fermentation of renewable resources such as corn, sugar beet, wheat and other starch-rich products (Cabedo et al. 2006). NatureWorks LLC (formerly Cargill Dow) is the best known commercial producer of PLA, known by its trade name NatureWorks PLA. In addition to being biodegradable, PLA is compostable in commercial composting facilities (Platt 2006). However, it is not usually home compostable due to the required thickness of the material (P. Skelton pers. comm.). It is breathable (porous) and suitable for films on fruit and vegetable pre-packs but unsuitable for use in bottles.(b) Polycaprolactone (PCL)PCL is probably the most important biodegradable synthetic aliphatic polyester on a commercial basis (Platt 2006). Degradation of this polymer can take up to two years and consequently copolymers have been synthesised to accelerate degradation. For example, PCL-polyester/starch blends are used to produce the commercial product Mater-Bi described below (Platt 2006). 4.3.3 Modified biodegradable biopolymersThese polymers have evolved in an attempt to improve the biodegradability of synthetic polymers by incorporating polysaccharide-derived materials. The best known commercial polymer in this class is Mater-Bi produced by Novamont. There are various grades of Mater-Bi produced from starch and different classes of synthetic components such as PCL. Mater-Bi is used in a wide range of applications including, food waste bags, carrier bags, garden waste collection bags and fresh food (fruit and vegetable) packaging.

4.4 Partially Biodegradable and Oxo-degradable PolymersThere have been various approaches towards improving the degradability of inert polymers, including the development of blends of biodegradable and non-biodegradable polymers, and polymer modification through the insertion of “weak links” or chemical additives to polymers (Chandra & Rustgi 1998).(a) Blends of biodegradable and non-biodegradable polymersBiodegradable polymers, such as starch, are blended with inert polymers, such as polyethylene. The rational behind the development of these copolymers is that if the biodegradable polymer is present in a sufficient quantity and is subject to microbial breakdown, then the inert polymer fragment remaining should lose its integrity and disintegrate (Chandra & Rustgi 1998). To maintain the mechanical properties of the polyethylene, small quantities of starch must be used (Chandra & Rustgi 1998). These blends are therefore only partially biodegradable (Arvanitoyannis et al. 1998). (b) Polymer modification to facilitate biodegradationWeak links are designed to allow controlled degradation of the polymer to a lower molecular weight product which can be broken down by micro-organisms. Carbon monoxide and vinyl ketones may be used to produce photodegradable copolymers of ethylene (weak links) and these materials have been used to produce the six-pack retaining rings for canned beverages (Klemchuk 1990).

Various additives, including Totally Degradable Plastics Additives (TDPATM) developed by Environmental Products Inc (EPI), ferric compounds, benzophenones and titanium or zirconium chelates, to inert polymers have been used to sensitise photodegradation (Klemchuk 1990). These oxy-degradable polymers are used commercially in carrier bags and food packaging and containers. They do not meet any biodegradability standards and this has stimulated recent activity to develop a new standard for these materials (E. Nichols pers. comm.). Biodegradation of photodegraded polymer particles is slow and has the potential to lead to a build up of

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inert polymer residues in the environment (Skelton 2008).

4.5 Degradation of Biodegradable Plastics and PolymersBiodegradation of polymers is a two step process where initially the polymer is depolymerised and then the products mineralised. Extracellular enzymes from microorganisms bring about the depolymerisation. The resulting fragments are transported into the microbial cell where they are mineralised, producing gases, water, salts, minerals and biomass. This biological activity will concur or be initiated by non-biological degradation such as photodegradation and hydrolysis (Platt 2006). There are therefore a number of interacting factors of polymer chemistry and biotic and abiotic disposal environment which affect biodegradation.

4.5.2 Organisms and enzymes involved in biodegradation(a) Bacteria and actinomycetesBacteria shown to degrade biodegradable polymers in the environment are found in a number of families, including, Pseudonocardiaceae, Micromonosporaceae, Thermomonosporaceae, Streptosporangiaceae and Streptomycetaceae (Philip et al. 2007; Degli-Innocenti 2002). These are active under mesophilic and thermophilic conditions.(b) Fungi A number of fungi have been shown to degrade plastics in the environment. These include mesophiles (15 - 42°C optimum for growth) Aspergillus niger, Aspergillus flavus, Candida lipolytica, Penicillium furniculosum, Chaetomium globosum, Mucor pusillus, Phanerochaete chrysosporium, Pullularia pullulans and thermophiles (45 - 55°C optimum for growth) Chaetomium thermophile, Humicola lanuginosa and Torula thermophile (Orhan & Büyükgüngör 2000; Gusse et al. 2006; Dhanasekaran et al. 2007).(c) EnzymesCellulose, starch and PHA are all polysaccharides but are broken down by different enzymes. Cellulose is broken down by cellulases (β, 1-4 glucanases). Many fungi can digest cellulose whereas cellulose digestion in bacteria is restricted to a few groups, including Sporocytophaga, Cytophaga and actinomycetes (Brock et al. 1994). Starch is broken down by many fungi and bacteria by the starch-digesting enzymes, amylases. PHA is broken down by the action of extracellular PHA depolymerases. Both bacteria, including Alcaligenes, Bacillus, Pseudomonas and Streptomyces spp., and fungi, including Penicillium funiculosum and Fusarium solani, have the ability to degrade PHA (Jendrossek et al. 1996; Jendrossek & Handrick 2002). Cutinase produced by Fusarium solani has also been shown to hydrolyse PCL (Murphy et al. 1996). PLA has been shown to be degraded by a PLA depolymerase secreted by the actinomycete Amycolatopsis sp. (Nakamura et al. 2001) and by a protease, with substrate specificity similar to commercial proteinase K, produced by Tritirachium album (Jarerat & Tokiwa 2001).(d) EarthwormsResearch using radio-labelled polymers has shown that Eisinia andrei earthworms bioassimilate PLA as indicated by a weight gain (Vert et al. 2002). The ability of earthworms to degrade and bioassimilate polymers is however dependent on the type of polymer, in that four species of earthworm (Lumbricus terrestris, Aporectodea trapezoides, A. tuberculata and E. fetida) showed no activity towards starch/polyethylene films (Tsao et al. 1993). However, the timescale of this study was very short (10 days) and possibly a higher density of earthworms and/or polymer may be needed to facilitate primary degradation. Biodegradable plastics are only likely to be attractive to earthworms once they start to decompose but they may assist in fragmentation (J. Frederickson pers. comm.).

Lignin and plastic polymer (PCL) degradation have also been found to be higher in vermicompost made mesophilically by the action of earthworms on plant and animal wastes than in green waste compost made thermophilically from plant debris (Anastasi et al. 2004). 4.5.3 Effect of composting conditions on biodegradation of polymersThere are a number of environmental parameters which may vary in any one niche and have an effect on biodegradation of polymers (De Wilde 2005). These are: moisture content, oxygen availability, temperature, chemical environment (pH, salt concentration, radiation (UV light) and microbial population. These parameters all have an impact on the microbial community. They determine the species diversity of the community as well as the microbial activity.

The composting conditions under which the biodegradation of plastics have been examined, or are specified in standards, are summarised in Table 4 (Appendix). The majority of these studies have been conducted in laboratory-scale equipment although some studies have been conducted in large-scale windrow or in-vessel systems (Tables 4 and 5, Appendix). There is no published information on the composting of plastics/polymers in small-scale, self-heating composting bins.(a) MoistureThe moisture content of compost is important for microbial growth and a moisture content of 50% is recommended for the production of compost (Day & Shaw 2001; BSI PAS 100:2005). In addition, hydrolysis plays a major role in the biodegradation of some polymers (e.g. PLA) and hence polymers will tend to biodegrade faster in moisture-rich composts than in dry conditions (Kale et al. 2007). For example, Gu et al. (1994) examined the biodegradation, measured as weight loss, of cellulose acetate and cellulose films in various synthetic compost mixtures in laboratory-scale aerated compost reactors maintained at 53oC. They found a decrease in moisture content from 60% to 40% w/w resulted in an increase in the time required for complete disappearance of the

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materials. Most studies on compostability of plastics have been conducted in the range 47-70% w/w moisture (Table 4, Appendix). (b) TemperatureGenerally, the rate of biodegradation increases with compost temperature to an optimum. For example, the rate of biodegradation of PLA films increased from 25 to 55˚C (Kale et al. 2007). Most of the experiments on compostability of plastics have been conducted at optimum temperatures of 52-65˚C (Table 1). Jayasekara et al. (2003) found that a starch-polyester blend biodegraded in compost at 22˚C in under 7 weeks. A number of research papers have examined biodegradation at lower temperatures in soil and other media (Table A4, Appendix).(c) Aeration/oxygenationBiodegradation of polymers in aerobic conditions may be totally different than that in anaerobic conditions. For example PCL did not biodegrade at all and PLA biodegradation was less than 10% in anaerobic conditions (Kale et al. 2007). The majority of experiments in Table 1 were conducted under aerobic conditions with aeration or turning.(d) FeedstocksPrevious studies on compostability of plastics have been conducted over a wide range of C:N ratios using a diverse range of waste feedstocks to mix with the test material (Table 1). Very few of the studies have compared compostability of plastics using different feedstock wastes. Biodegradation of cellulose acetate and cellulose films in various synthetic compost mixtures prepared from tree leaves, shredded paper, food, meat, cow manure, sawdust, metal shavings, alfalfa, glass, urea, starch, pet food and a compost seed, was shown to be dependent on the formulation of the compost (Gu et al. 1994; Gross et al. 1995). However, no direct correlation between the C:N ratio (ranging from 13.9 to 61.4) and biodegradation was observed.

The majority of experiments have been conducted using incorporation rates of plastics in the compost matrix of 14% w/w or less (Table 4). Ghorpade et al. (2001) found that the addition of 10 and 30% w/w PLA to compost produced similar amounts of CO2. The authors suggest that the reduction in pH recorded with 30% PLA may have suppressed microbial activity during composting.(e) Sample size and thicknessThe dimensions and thickness of plastic samples in previous research is very diverse (Table 5, Appendix) and this will have significant effect on the rate of biodegradation in both industrial and home scale composting systems (T. Breton pers. comm.). Plastics do not easily shred for preparation for composting (E. Nichols, pers. comm.). Packaging standards involve composting the material in the form it is to be used and some studies have examined compostability of bottles and other containers (Table 2).

4.6 Standards for Testing Biodegradability of PackagingVarious organisations have developed standardised test methods and criteria to deem a material biodegradable or compostable in order that these claims can be supported for marketing or regulatory purposes. These include the American Society for Testing and Materials (ASTM), Comité Européen de Nomalisation (CEN), Deutsches Institut für Normung eV (DIN), Japanese Institute for Standardisation (JIS) and the International Organisation for Standardisation (ISO).

The most commonly used methods for assessing the biodegradability of materials involve monitoring microbial growth (measurement of CO2 evolved), depletion of substrates (mass loss), reaction products and changes in substrate properties and/or appearance (Platt 2006). Different standards have therefore been developed for testing and acceptance criteria in different environmental niches.

Whenever a material or product is tested for compliance with the EN13432 or the OK Compost Home specification, a maximum thickness is specified. So, for example, Novamont's NF01U grade is certified to EN13432 at a maximum of 100 microns and to 67 microns for OK Compost Home. Individual companies then have to determine what thickness they wish to certify their finished or semi-finished products (T. Breton pers. comm.).

4.6.1 European standards for compostability of packagingBS EN 13432: 2000 - Packaging – Requirements for packaging recoverable through composting and biodegradation – Test scheme and evaluation criteria for the final acceptance of packaging.This standard specifies requirements and procedures to determine the compostability and anaerobic treatability of packaging and packaging materials in terms of biodegradability, disintegration during biological treatment, effect on the biological treatment process and effect on the quality of the resulting compost.

Table 1: Conditions for testing the compostability of plastics/polymers in research papers and test standardsPlastic/Polymer % w/w

Wastes System Temp (oC)

Timeweeks

Moisture(% w/w)

C:N ratio

pH Reference/Standard

PLA 10,30

green waste, wood lab-scale 52 32 49-55 c. 6 Weber 2003

Polyethylene food & green wastes windrow 24-52 12 47 18 Davis et al. 2005

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(a) Chemical characteristicsPackaging, packaging materials and packaging components should contain a minimum of 50% of volatile solids and must not exceed the stated levels of various heavy metals and other toxic and hazardous substances.(b) BiodegradabilityThe total proportion of organic constituents without determined biodegradability shall not exceed 5%. The period of application for the test should be a maximum of 6 months. The percentage of biodegradation should be at least 90% in total or 90% of the maximum degradation of a suitable reference substance after a plateau has been reached for both test material and reference substance. The limit value for biodegradation is based on conversion of the carbon of the test material into CO2 and biomass. The reference substance, a micro-crystalline cellulose powder, has to be degraded according to the validity criteria stated in the respective test methods.(c) DisintegrationFollowing submission to the composting process for a maximum of twelve weeks, not more than 10% of the original dry weight of test material shall fail to pass through a >2 mm fraction sieve.(d) EcotoxicityThe germination rate and the plant biomass of two standard plant species selected in the sample composts should be more than 90% of those from the corresponding blank.

Table 2: Methodology and results for testing compostability of plastics/polymers in research papers and standards

Plastic/Polymer Test Standard Size, cm2

or formThicknessm

Biodegrad-ability (%)*

Reference/Standard

PLA 0% PLA 18.1-37.5 1000-1500 C Weber 2003Polyethylene 0% polyethylene 600 5-8 M Davis et al. 2005Mater-Bi ZF03U paper bag 100 30 70-83 M Silvestri et al. 1996PHBV cellulose powder granules 88 C Pagga et al. 1995TDPA-based polyethylene

0% TDPA-based polyethylene

25 63 M Raninger et al. 2002

Mater-Bi Z grades cellulose 74-100 C Boelens 1992PCL, PCL-lignin, PVA filter paper 60, 40-60, 25

CChiellini & Corti 2003

Cellulose acetate, PCL 20-38 2-100, 100 M Gardner et al. 1994PLA 0% PLA 18.8 1500 C Ghorpade et al. 2001Cellulose acetate autoclaved compost

with KCN addition4 25-51 c. 70-80

C&MGu et al. 1994Gross et al. 1995

PLA bottles cellulose powder bottle 77-84 C Kale et al. 2007

Mater-Bi 564 100 M Mohee & Unmar 2007

Plastic with PDQ-H α-cellulose 4 19.3 C Mohee & Unmar 2007

Mater-Bi cellulose filter paper 0.25-0.5 27.1 M Mohee et al. 2007EPI product with TDPA cellulose filter paper 0.25-0.5 0 M Mohee et al. 2007Mater-Bi Z101U 100-150 450 98.9 M Piccinini et al. 1996EPI TDPA polyethylene >60 D Raninger & Steiner

2000Mater-Bi 28 c. 100 M Ruco & Pesca 2005EPI TDPA polyethylene 28 0 M Ruco & Pesca 2005Polyethylene 28 0 M Ruco & Pesca 2005Polymers-starch blend blank compost 50 68 C Starnecker & Menner

1996PCL powder 40-560 c. 80 C Starnecker & Menner

1996Cyclodextrins cellulose fine

powder0-100 C Verstichel et al. 2004

Starch-polyester blend cellulose c. 100 C Jayasekara et al. 2003PLA 4 610-710 c. 30

C&MGattin et al. 2001

Starch-based film 4 820-920 >90 C&M

Gattin et al. 2001

Standard cellulose powder final form 90 C BS EN 13432:2000Standard cellulose powder final form 90 C BS EN 14995: 2006Standard cellulose powder

(<20 m)4 (max) >70% after

45 days CBS ISO 14855

Standard final form D BS ISO 16929: 2002Standard cellophane, PHBV,

cellulose acetate (+),HDPE (-)

D 5509 - 96

Standard cellulose or starch C&M D 6002 - 96

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* Biodegradability based on CO2 evolved (C), mass loss (M) or disintegration (D)

BS EN 14995: 2006 - Plastics – Evaluation of compostability – Test scheme and specificationsThis standard specifies requirements and procedures to determine the compostability or anaerobic treatability of plastic materials in terms of biodegradability, disintegration during biological treatment, effect on the biological treatment process and effect on the quality of the resulting compost. The evaluation criteria are the same as for BS EN 13432: 2000.

BS ISO 14855: 1999 - Determination of the ultimate aerobic biodegradability and disintegration of plastic materials under controlled composting conditions – Method by analysis of evolved carbon dioxideThis standard specifies a method for the determination of the ultimate aerobic biodegradability of plastics, based on organic compounds, under controlled composting conditions by measurement of the amount of CO2 evolved and the degree of disintegration of the plastic at the end of the test. The inoculum used consists of stabilised, mature compost derived, if possible, from composting the organic fraction of solid municipal waste. The test material is mixed with the inoculum (1:6 dry matter w/w) and introduced into a static composting vessel where it is intensively composted under optimum oxygen (aerobic), temperature (58oC 2 oC) and moisture (50% w/w) conditions for a test period not exceeding 6 months. During aerobic degradation of the test material, CO2 produced is continuously monitored, or measured at regular intervals, in test and blank vessels to determine the cumulative CO2 production. The percentage biodegradation is given by the ratio of the CO2 produced from the test material to the maximum theoretical amount of CO2 that can be produced from the test material. The percentage biodegradation does not include the amount of carbon converted to new cell biomass which is not metabolised in turn to CO2 during the course of the test. The degree of disintegration of the test material is determined at the end of the test, and the loss in mass of the test material may also be determined.

BS ISO 16929: 2002 - Plastics – Determination of the degree of disintegration of plastic materials under defined composting conditions in a pilot-scale testThis standard is used to determine the degree of disintegration of plastic materials in a pilot-scale aerobic composting test under defined conditions. The test material is mixed with fresh biowaste in a precise concentration (for measurement of the degree of disintegration, compost analysis and ecotoxicity in one test, 1% on wet mass basis of test material in its final form plus, 9% on wet mass basis of test material as powder or granules) and introduced into a defined composting environment. The composting environment may be either a pilot-scale composting bin or nets buried in a pilot-scale composting bin. The volume of each bin should be high enough for natural self-heating to occur. A natural ubiquitous microbial population will start the composting process spontaneously and the temperature will increase. The composting mass is regularly turned over and mixed. Temperature, pH, moisture content and gas composition are monitored regularly to ensure they fulfil certain requirements (pH >5, moisture content >40% by mass, and oxygen content inside the composting material >10%) to permit appropriate microbial activity. The composting process is continued until a fully stabilised compost is obtained, usually after 12 weeks. The compost is visually observed at regular time intervals to detect any adverse effect (structure, moisture, fungal development) of the test material on the composting process. At the end of the test, the maturity of the compost is determined and the mixture of compost and test material is sieved through 2 mm and 10 mm mesh sieves. The disintegration of the test material is evaluated on the basis of the total dry solids by comparing the fraction of test material retained by the 2 mm sieve and the amount tested.

In addition to complying with the Standards required to certify a material as biodegradable, European Union rules allow no more than 10% of a non-biodegradable ingredient in a biodegradable material for the entire composition to be classified as biodegradable (Schut 2007).

4.6.2 American standards for compostability and packagingThe American Society for Testing and Materials (ASTM) has also developed a number of standards relevant to determining the compostability of plastic materials.

D 5509 – 96 - Standard practice for exposing plastics to a simulated compost environmentThis Standard covers the exposure of plastics to a specific test environment i.e. simulated solid waste (food, garden, paper, plastic, textile, wood wastes) or yard waste (hay, tree leaves, twigs) mixtures, an inoculum consisting of an unsterilised composted potting-soil mixture or material from a commercial composting process, 50-60% w/w moisture, aerobic, maintained at a maximum temperature of 50-60oC in a laboratory-scale reactor that simulates a self-heating composting system that uses aeration to control maximum temperature.

D 6002 – 96 - Standard guide for assessing the compostability of environmentally degradable plasticsThis guide covers suggested criteria, procedures, and a general approach to establish the compostability of environmentally degradable plastics. It uses a tiered criteria-based approach to assess the compostability of environmentally degradable plastic products. The tiers progress from rapid screening of polymeric materials and other organic components to determine biodegradability (based on CO2 production) to relatively long term, more

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complex/higher cost evaluations.

D 6003 – 96 - Standard test method for determining weight loss from plastic materials exposed to simulated municipal solid waste (MSW) aerobic compost environmentThis test method is used to determine the degree and rate of aerobic biodegradation of plastic materials exposed to a controlled composting environment (aerobic, temperature controlled to simulate self-heating and cooling). Biodegradability of the plastic is assessed by determining the amount of weight loss from samples exposed to a biologically active compost relative to a “poisoned” (abiotic) control (sterilised compost with the addition of potassium cyanide).

D 5338 – 98 (2003) - Standard test method for determining aerobic biodegradation of plastic materials under controlled composting conditionsThis test method determines the degree and rate of aerobic biodegradation (based on CO2 production) of plastic materials on exposure to a controlled-composting environment under laboratory conditions.

D 6400 – 04 – Standard specification for compostable plasticsThis specification covers plastics and products made from plastics that are designed to be composted in municipal and industrial aerobic composting facilities. It has similar evaluation criteria to BS EN 13432: disintegration during composting (following 12 weeks in a controlled composting test, no more than 10% of the original dry weight of the test material remains after sieving through a 2 mm fraction sieve), inherent biodegradation (at least 60% of the organic carbon must be converted to CO2 after 6 months) and ecotoxicity (test material should have concentrations of regulated heavy metals less than 50% of those prescribed for sludges or composts in the country where the material is sold and, the germination rate and plant biomass of two standard plant species selected in sample composts should be no less than 90% of those in the corresponding blank composts).

4.6.3 Standards for compost qualityIn the UK, the British Standards Institution Publicly Available Specification 100 (BSI PAS 100: 2005) covers the entire process by which compost is produced, from raw materials and production methods, through to quality control and laboratory testing. This specification is for biodegradable materials that have been kept separate from non-biodegradables, and can apply to composted materials produced at centralised, on-farm and community composting facilities. It is not applicable to small-scale composting operations (home composting). This standard has been developed through the Environment Agency (Anon. 2007b). In this document the biodegradable films and packaging acceptable for the production of quality compost are specified.Waste plastic (EWC 20 01 39) is allowed only if independently certified compliant with EN 14995 and used for the collection of source-segregated biowaste. Examples are kitchen caddie liners, bin liners and biowaste collection sacks.

4.6.4 Certification and logosIn order that the consumer and recycling authorities have confidence in any claims of the properties of a material it is important that they are verified. Towards this, certification schemes have been set up to verify the compostability of these materials. The logos of these certification schemes are shown in Fig.1 (Appendix).(a) DIN CERTCOThe German quality control organisation, DIN CERTCO, is probably the best known and most used body responsible for testing and certifying biodegradable and compostable polymers and products. It licenses the use of the compostable logo developed by European Bioplastics (previously IBAW). The certification is based on BS EN 13432. (b) OK CompostIn Belgium, the quality control organisation AIB-Vinçotte International developed the OK Compost compostability certification and labelling system. This certification relates to materials that are subjected to industrial-scale composting conditions and is based on BS EN 13432. (c) OK Compost HomeAn OK Compost Home logo has been developed for materials that will compost under conditions aimed to simulate those found in home composting bins (Anon. 2005). This label is awarded to material that shows at least 90% degradation at ambient temperature (20oC) in 180 days (Breton 2007). There are significant difference between these simulated conditions and those found in real home composting bins. As noted in Section 1, 20oC is rarely achieved in the UK and the composting duration is usually much longer. A composted material is used in the simulated test (which gives good adhesion to the test plastic) whereas mixed wastes are added at regular intervals in a real bin.

There is currently no European-wide home composting standard although work is underway (Anon. 2007a) and a “home-compostable” on-pack logo for the UK could be available by autumn according to The Composting Association (Ellis 2008). Although a home compostable logo on packaging in the UK is planned for later this year, there are few products that comply with the home compostable criteria (E. Nichols pers. comm.). Novamont's NF01U grade satisfies the criteria for OK Compost Home at a maximum of 67 microns (T. Breton pers. comm.).

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(c) Biodegradable Products Institute - US Composting CouncilIn the USA, a compostability certification and logo (‘Compostable’) programme was started in 2000 by a joint effort of the Biodegradable Products Institute (BPI) and the US Composting Council (USCC). The certification programme is based on ASTM D 6400 and ASTM D 6868 (Standard specification for biodegradable plastics usedas coatings on paper and other compostable substrates). In addition to certification schemes that evaluate compostability, others are related to environmental fate and safety e.g. the Biodegradable Plastics Society (Japan) “GreenPla” certification, or to biodegradation in soil or water, e.g. Belgian OK Biodegradable (De Wilde 2005).Certification allows compostable materials to carry a compostable logo and communicate this information to waste disposal operators and product image to consumers.

4.6.5 Comparison of standards methodologiesThe Standards used to evaluate the biodegradability of a material are based on simulated controlled composting conditions (Pagga 1998). There are however few studies which compare biodegradability in real and simulated conditions Tables 3,4 and 5 Appendix).

Ultimate biodegradation in compost can only be measured if all carbon in the test material is mineralised to CO2. The use of solid materials, such as soil and compost, as incubation media in respirometric experiments may have a negative effect on the accuracy of the test as some of the carbon may be incorporated into biologically-stable humic substances and/or background CO2 released from the media may be enhanced by the addition of a test material (Starnecker & Menner, 1996). To attempt to overcome these problems, Starnecker & Menner developed a method where compost/soil was replaced with inert, carbon-free packing material which could simulate similar conditions to those found in compost. They found the rate of biodegradation of a starch-based material using this method similar to that in compost. As the starch-based material is the sole source of carbon using this method, a carbon mass balance for the assessment of ultimate biodegradation can be calculated. Kale et al. (2007) found that the biodegradability of PLA bottles by measuring the CO2 evolved and by measuring PLA weight loss produced similar results. Degradation under the simulated composting conditions gave an indication of the biodegradability under real composting conditions. Chiellini & Corti (2003) diluted soil and compost with perlite to ensure optimal conditions for microbial growth and reduce CO2 production from the blanks. The authors suggest that this procedure would allow small differences in the biodegradation rate of materials to be identified, and be useful in longer-term (>6 months) degradation studies.

4.7 Composting of Biodegradable Polymers

4.7.1 Comparison of biodegradability of materialsThere have been few published comparisons of materials for biodegradability under identical conditions. Barak et al. (1991) evaluated the biodegradation of two materials developed for enhanced biodegradability, polyhydroxybutyrate copolymerised with hydroxyvalerate (PHBV) and LDPE incorporated with a starch filler. The PHBV required at least 44 days to degrade whereas the LDPE-starch blends degraded within 14 days under the same test conditions.

Krupp & Jewell (1992) tested the biodegradability of 12 modified plastic films in anaerobic and aerobic bioreactors. Only one of the test films, a poly(hydroxybutyrate) poly(hydroxyvalerate) copolymer, was considerably biodegraded (90-100% mass loss) in this study.

Biodegradation of a series of cellulose acetate films was compared with commercially available biodegradable polymers, PHB, PHBV, PCL and Novamont Mater-Bi) in a laboratory composting system (Gardner et al. 1994). Film disintegration and weight loss of the cellulose acetate films were comparable to PHBV and PCL. The PHB films failed to disintegrate, partly due to the thickness of the film. The Mater-Bi film was also present at the end of the composting process but had lost almost half its original weight.

Biodegradation of various grades of Mater-Bi was shown to be comparable to a cellulose control in a simulated composting environment (Bastioli & Innocenti 1996). When added to a commercial windrow at a rate of 0.12%, Mater-Bi Z101U showed 98.9% degradation after 4 months, with no effect on the composting process or composition of the final product (Piccinini et al. 1996).

Ruco & Pesca (2005) compared the disintegration of three types of plastic bags made from Mater-Bi, an oxy-degradable plastic and polyethylene, under laboratory-scale composting conditions. After 90 days at 58oC, the oxy-degradable and polyethylene bags were intact and visible whereas there were no residues of the Mater-Bi bags in the compost.

Mohee et al. (2007) assessed the biodegradability of two materials, Mater-Bi, and EPI material containing 3% of TDPA, under aerobic and anaerobic conditions. Biodegradation of the materials was monitored in terms of mass loss and the production of biogas (methane). Mater-Bi showed 27.1% biodegradation on a dry weight basis after 72 days of aerobic composting and produced 245 ml of methane over 32 days which was similar (246.8 ml) to that produced by the positive control (cellulose filter paper). However, the EPI material produced very little methane (7.6 ml) and did not biodegrade under aerobic or anaerobic conditions. Mohee & Unmar (2007) compared the biodegradability of two plastics containing degradable additives with that of a biodegradable and compostable plastic bag (Mater-Bi product). After 55 days composting, the Mater-Bi bags had completely degraded whereas the two test plastics did not undergo significant degradation.

Cimmino et al. (2002) assessed the biodegradation of polypropylene-based films modified with natural

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terpene resin, poly (α-pinene). A microbial consortium, isolated from soil rich in plastic wastes, was added to artificial liquid media in shake flasks with these materials as the sole carbon source, and incubated at 28oC for up to 6 months. The microbial consortium was shown to degrade the blends of films but not the polypropylene film on its own.

4.7.2 Partially biodegradable and oxo-degradable polymersThese polymers do not conform to standard EN 13432 as they leave small fragment residues after the specified biodegradation process. There is no standard available for testing their degradation behaviour in the environment (E. Nichols pers. comm.). EPI TDPA polyethylene degraded by 60% in 26 weeks in an industrial composting system, which is below the requirement for EN 13432 (Raninger & Steiner 2000; Raninger et al., 2002). The BSI has produced a framework for testing oxo-degradable polymers (E. Nichols pers. comm.). This will allow oxo-degradable polymer manufacturers to develop innovative tests in terms of degradation. A report format for testing will be established, rather than pass/fail criteria, with a move away from compostability.

4.7.3 Effects of biodegradable polymers on compost end-useOne of the criteria in EN 13432 is that the biodegradable polymer should not adversely affect the quality of the final compost. A study investigated the effect of compost derived from mixed biodegradable packaging, made of starch or starch blends, and organic waste, composted on an industrial-scale compost site, on the quality of the final compost (Klauss & Bidlingmaier 2004). The compost produced showed no differences in quality parameters compared with compost produced from organic waste only. A demonstration field trial using the compost produced with the biodegradable packaging had the same positive effect on soil and plant characteristics as the conventional compost, although the inclusion rate of biodegradable packaging was only 1% w/w. This compares with an inclusion rate of biodegradable packing in compost of 14.3% w/w dry matter in EN 14855.

Ghorpade et al. (2001) reported that PLA was degraded when added to pre-composted yard waste in a laboratory composting system. The addition of 30% PLA to the yard waste resulted in a drop in compost pH from 6.0 to 4.0 after 4 weeks composting, presumably as a result of chemical hydrolysis of the PLA and lactic acid generation. No change in pH was detected with the addition of 10% PLA.

Raininger (et al., 2002) reported that the inclusion of 1.1% w/w of bags of the oxo-degradable polymer EPI TDPA did not adversely affect the final quality of the compost. However, this inclusion rate is low, and higher rates conforming to EN 14855 were not investigated.

CONCLUSIONS OF THE LITERATURE REVIEW AND CONSULTATIONS Home Composting System Environment1. The composting environment within home systems differs from that in industrial-scale systems in terms of

lower temperatures (particularly in winter), higher oxygen levels, and greater variability in waste feedstock degradation and mixing.

2. The predominant compost organisms responsible for degradation and their levels of activity differ between home scale and industrial scale systems. In large scale systems, mesophilic and thermophilic microorganisms are most important and are highly active; in small scale systems, mesophilic and psychrophic microorganisms normally predominate at low levels of activity, and earthworm activity can also be significant.

Pesticides in Home Composting Systems3. The most likely source of pesticide contamination of waste feedstocks in home composting systems is from

residues of lawn care herbicides on grass clippings from spring to late summer. The most widely used lawn care herbicides are 2,4-D, mecoprop-P and MCPA. Dicamba, dichlorprop, chorpyralid and fluroxpyr are also used.

4. There has been little research on the direct effect of pesticides on compost organisms but the behaviour of a particular pesticide and its degradation in soil, which has been extensively researched, should be a reasonable approximation of what occurs during composting.

5. Thermophilic composting can enhance pesticide removal by microbial degradation and volatilisation. This is less likely to occur in home composting systems, and organic matter can increase the sorption and reduce the microbial availability of some pesticides. However, composts generally enhance the degradation of pesticides over that obtained in soil, even at ambient temperatures.

6. The most toxic and recalcitrant pesticides during composting are OCs and the OP diazinon, but these are no longer approved for use. The majority of OP and carbamate insecticides and herbicides are less toxic to compost organisms and degrade readily.

7. Herbicides are generally less toxic to soil microbes and earthworms (and therefore probably less toxic to compost organisms) than insecticides and fungicides.

8. Based on typical patterns of use, toxicity and degradation, the risk posed by pesticides to the composting process in home systems and to the end use of the compost is very small.

Biodegradable packaging and films in Home Composting Systems

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9. Most of the experiments and testing standards on the compostability of plastics have been conducted at optimum temperatures for their biodegradation of 52-65˚C. There is no published information on the composting of plastics/polymers in small-scale home composting bins that typically operate at close to ambient temperatures.

10. AIB-Vinçotte International has developed an OK Compost Home logo for materials that will compost under conditions aimed to simulate some of those found in home composting bins, i.e. materials that show at least 90% degradation at ambient temperature (20oC) in 180 days. However, there are significant differences between these ‘simulated’ conditions and those that actually occur in real home composting bins.

11. Very few products have met the requirements of OK Compost Home, e.g. films and plastic bags made from Novamont’s Mater-Bi.

12. Previous research on the compostability of plastics has been conducted using a diverse range of plastic inclusion rates and composting conditions (wastes, moisture content, aeration). These factors are likely to have significant effects on the rate of biodegradation of plastics and the variability makes it difficult to compare results obtained from different researchers and/or with different materials.

13. There is some evidence that compostable plastics biodegrade more rapidly in the presence of earthworms, by ingestion and/or by enhanced degradation in vermicomposts.

14. Previous studies on the ecotoxicity of oxo-degradable plastics have generally been conducted at low inclusion rates. There is a lack of information on effect of high inclusion rates of these materials, in soil and in compost, on the growth of microorganisms, fauna and plants over time.

RECOMMENDATIONS FOR FUTURE RESEARCH

These recommendations are aimed at maximising the amount of compostable plastic packaging that can be composted in home composting systems, and diverting waste from landfill where it will generate methane under anaerobic conditions.

1. The compostability of biodegradable plastics needs to be tested in actual home composting systems and comparisons made with degradation under ‘optimum conditions’.

2. In the research, the effects of typical temperatures and feedstocks, composting durations and gradual filling of home composting systems on the rate of composting of plastics should be examined.

3. The proportion of compostable plastic that can be mixed with other organic wastes without adversely affecting the composting process or the final quality of the compost needs to be determined.

4. The inter-relationship between compostable plastics, microorgansims and earthworms should be investigated further in home composting systems.

5. More information is needed on the ecotoxicity of oxo-degradable plastics in composts and soils, particularly the effect on microorganisms, fauna and plants.

References to published material9. This section should be used to record links (hypertext links where possible) or references to other

published material generated by, or relating to this project.

A list of references is provided in the Appendix to this report.

Consultations were made with following:

Paul Alexander, Royal Horticultural SocietyTony Breton, Novamont S.p.A.Alan Campbell, Dr David Cava, Chipping Campden Food Research AssociationDr Jim Frederickson, Open UniversityDr Kerry Kirwan, Warwick Manufacturing Group, University of WarwickDr Margi Lennartsson, Garden OrganicEmily Nichols, Kiara Zennaro, The Composting AssociationDr John Pickering, Organic Resource AgencyPeter Skelton, WRAP

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