e Pergamon

PH: S0273-1223(98)00257-1

Waf. Sci. Tech. Vol. 37, No.8, pp. 19-25,1998.© 1998 IAWQ. Published by Elsevier Science Ltd

Printed in Great Britain.0273-1223/98 $19'00 + 0'00

PESTICIDES - FRIEND OR FOE?

Mervyn Richardson

Birch Assessment Services For Information On Chemicals (BASIC), 6 Birch Drive,Maple Cross, Rickmansworth. Hertfordshire WD3 2UL. UK

ABSTRACT

Pesticides, where used correctly, can save up to 40% in crop losses; however, when pesticides are mal-, mis­or over-used the environmental and public health consequences can be very considerable. The UnitedNations has issued a list of chemicals that are banned or severely restricted in use; many of the chemicals onthis list are pesticides. Whilst the use of highly persistent pesticides such as DDT has proved very effectivein the eradication of diseases such as malaria, the adverse effects to the natural environment have beendevastating - whole populations of birds have been eliminated.

Within the fonner Soviet Union, the use of highly persistent pesticides was widespread; this has resulted incontamination of both crops, with pesticide residues well in excess of internationally acceptable maximumresidue limits, and water resources to such high level that remediation through natural processes will takedecades, or by xenobiotic or physicochemical processes will be extremely costly. This is an extraordinarysituation as the fanner Soviet Union had one of the most stringent of environmental regulation - the GOSTregulations; unfortunately these were not pragmatic and rarely applied. When in the Ukraine in 1994, I heardthat fanners where paid for every application made; the result was crops, soil, water and the environmentwere highly contaminated, and in some cases the land became barren. Currently, the situation in somecountries is that no pesticides are being applied because under the new market conditions fanners cannotafford to purchase pesticides. In Annenia in July 1995, one could not purchase fruit which was not diseased.

The effects of mis-use of pesticides are known to cause very serious adverse effects to human health: in somecountries children are exhibiting excessive cancer incidences; crops found to be highly contaminated with upto five different pesticides are being condemned, often being burnt in the fields. As these crops in allprobability contained now banned and highly persistent pesticides, mere burning at low temperatures isproducing even more toxic dioxins. furans, etc. This leads to both air and soil contamination. One answerwould be for the fanner to be obliged to pay for high-temperature incineration in a high-tech incinerator in adeveloped country, which, subject to prior informed consent, could cost US $ 5000ltonne.

However, the application of modern pesticides in accordance with manufacturers' specifications can incurnone of these problems; this presentation will outline how pesticides can be used judiciously. © 1998 IAWQ.Published by Elsevier Science Ltd

KEYWORDS

Pesticides; mal-use; mis-use; over-use; legislation; crop residues.

WHAT IS KNOWN ABOUT PESTICIDE RESIDUES IN THE DIET

Our knowledge is far from complete and is variable. There arc about 600 pesticide chemical activeingredients registered for use on food crops; about ~5() or IIK'se aclive ingredients account for 98% of thepesticides applied and of that some 150 account for >X()'j;, or pesticides used in American agriculture. Forabout 50 older pesticides, tolerance levels cxist which were scl arbitrarily in the 1955-58 period, andgenerally are much higher than necessary,

19

20 M. RICHARDSON

From various monitoring studies, it is known that a significant portion of the food supply contains noresidues at levels that are detectable by the analytical methods used. Furthermore, the public should be madeaware of the fact that current monitoring results do not support a conclusion that a high percentage of food ispesticide residue free.

Table I. Numbers of samples analyzed, percentage of samples with no residues found, and violation rates fordomestic and import samples analyzed for pesticide residues in 1987-1993a

Year No ofsamples

DOMESTICSamples Violativewith no samplesresidues %

found

Sampleswith noresidues

found

llvIPORTViolative samples

%

% Over No to!' % Overtol. tol.

No tol.

1987 14492 58 1 1 56 <I 51988 18114 60 <1 1 62 <1 51989 18113 65 <1 <1 67 <1 31990 19146 60 <1 <1 64 <1 41991 18214 64 <1 <1 69 <1 21992 15370 65 <1 <1 66 <1 31993 12166b 65 <1 1 69 <1 1

lll~umbers of samples and violation rates for 1987 and 1988 are for surveillance plus compliance samples.For subsequent years, they are for surveillance samples only; ~oes Dot include 3022 samples of domesticand imported pears and tomatoes collected and analyzed under the statistically based study.

It should also be borne in mind that cooking can accelerate the conversion of purest compounds, e.g.daminozide and the ethylene dithio(bis-carbamates) to more toxic metabolites such as ethylene thiourea.Regrettably, toxicology data gaps persist, analytical methods are far from complete, and not all publishedtolerances are currently set at 'safe levels'.

WHAT IS NOT KNOWN ABOUT PESTICIDE RESIDUES

Society lacks consensus as to what level of risk is acceptable. There is no defensible basis upon which toestablish 'safe' tolerance levels. In the absence of a social consensus on an acceptable level of risk, the onlyarguable safe level is "zero risk".

PESTICIDE RESIDUES ANALYSIS: BASIC PRINCIPLES ANDPHILOSOPHIES

Determination of pesticide residues can be of interest for different purposes, viz.: i. establishment ofdegradation curves in samples from supervised trials; ii. checking of samples moving in trade forcompliance with legal maximum residue levels (MRLs); and iii. monitoring for the establishment of timetrends, total daily intake (TDI), etc.

The body of scientific evidence that there may be links between agrochemical exposure and some forms ofcancer is growing. In Denmark the Ministry for the Environment & Energy has recommended that 7

Pesticides 21

agrochemicals should be banned because they either threaten the environment or human health., viz.carbendazim, chlorothalonil, thiophanate methyl, bromoxynil, ioxynil, diazinon, and maleic hydrazide.

Table 2. Pesticide residues found in a variety of baby foods in 1990-1991. «Reprinted with permission fromYess etal., 1993).

No of samples analyzed/No of samples with residuesProduct type

Benomyl! Daninozide ETU N-methyl- Organochlorine"-thiabendazole carbamate Organophosphorusb

Baked products 18/0c/Od 24/0 29/1 18/0 27/0e/2Jf

Cereals 61/0/0 51/0 65/6 60/4 60/5/19

Comb. meat dinners 73/0/0 44/0 103/0 108/5 97/0/0

Comb. poultry dinners 61/0/0 40/0 72/0 68/0 63/0/0

Desserts 81/3/1 51/0 70/9 95/14 73/0/0

Fruits/fruit juices 346/8/11 327/2 310/38 431/62 333/5/0

Infant formulas 41/0/0 - 48/0 46/0 44/0/0

Vegetables 155/0/0 154/0 167/11 156/0 113/1/0

Total 836/11/12 691/2 864/65 982/85 810/11/42

"Chlorpyrifos is reported as an organochlorine pesticide; beach sample was analyzed for both types ofpesticide; Cno. samples with benomyl residues; dno. samples with thiabendazole residues; eno. samples;fno. samples with organophosporus residues.

Table 3. Frequency of occurrence of pesticide residues found in total diet study foods in 1991-1993a

Pesticideb

MalathionDDE,p,p'Chlorpyrifos-methylEndosulfanChlorpyrifosDieldrinChlorprophamMethamidophosDiazinonCarbarylCDicloranDimethoate

Total No of Findings

331998251162155142908372666157

Occurrence %

21191610109655444

"based on 6 market baskets collected between September 1991 and July 1993 and consisting of 1566 items.bisomers, metabolites, and related compounds are not listed separately; they are covered under the parentpesticide from which they arise.Creflects overall incidence; however, only 95 selected foods per market basket (i.e. 570 items total) wereanalyzed for N-methylcarbamates.

22 M. RICHARDSON

The Ministry has also proposed restrictions on a group of herbicides which would mean that 95% of theircurrent uses would no longer be possible, e.g. the phenoxy acid herbicides including 2,4-D, mecoprop anddichlorprop. The Danes were also due to introduce an Ecotax of 37% on insecticides, 15% on herbicides andfungicides and 3% on other pesticides from I January 1996. The move is part of the Danish Government's 10year reduction program to cut the volume of pesticide used by 50% by 1997. To compensate farmers, landtax is being cut from 10% to 5.7%.

WHAT IS REQUIRED TO BE KNOWN?

Pesticide regulatory processes would be greatly facilitated by improved information, increased clarity andmore consistent policies.

Risk standards need to be clarified and applied consistently with scientifically sound risk assessmentmethodologies and logical, consistent assumptions.More research and field testing efforts should be invested in developing actual residue data andpesticide dissipation curves under known conditions offield use, in each major climate region withinwhich a given crop is produced.More timely, accurate data are needed on actual pesticide use patterns:

i. number of applications;ii. rate of applications; andiii. pre-harvest intervals.

Special efforts should be targeted on newly introduced pesticides, for use with unusual pest problemsand for new cropping patterns.For pesticides not currently detectable, new low-cost and practical analytical methods should bedeveloped with special emphasis on widely used pesticides, especially for residues in drinking water.

CONSUMERS AND GOVERNMENT PERCEPTIONS

European Union

As part of the EU program to establish for the first time harmonized maximum pesticide residue levels(MRLs) for certain products of plant and animal origin, the European Commission has put forward a third adhoc priority list of pesticides for which it believes MRLs should urgently be established. In effect, theCommission's two draft Directives would amend the Annexes of Directives 90/6421EEC, 86/362IEEC and86/3631EEC.

The basis for the prioritization of the pesticides is their significance in agriculture and the potential for tradedifficulties due to the presence of residues in treated products. The harmonized lists should thereforefacilitate intra-EU trade in these products.

The proposals will establish MRLs for ten widely used pesticides that may leave residues in farm produceand were previously not covered by EU legislation. They will also extend the range of products covered byDirective 90/6421EEC to cover spices, which will allow MRLs to be set for ethylene oxide and propyleneoxide, as well as their associated reaction products. The pesticides covered by the proposal are:methidathion, methomyl, thiodicarb, amitraz, pirimiphosmethyl, fenthion, aldicarb, thiabendazole, ethyleneoxide, 2-chloroethanol, propylene oxide and chloropropanol.

In November 1990 a survey of consumers' perception of pesticide residues in food was conducted in theTokyo Metropolitan area. It involved 1100 consumers. Two-thirds of housewives recorded their concernabout pesticide residues, but their knowledge of basic pesticide properties was poor. Fifty-nine percent werefamiliar with the concept of GLP, and 46% with MRLs. Twenty-one percent were aware of decomposition

Pesticides 23

of pesticide residues in or on plants and animals. No response was recorded at 24%. Eighty-six percent wereconcerned about the effect of residues on their health and 71 % were concerned about the effects of residueson the environment. Fifty-seven percent agreed with the necessity of using pesticides to guarantee foodsupply.

PESTICIDE RESIDUES IN FOOD - IS THERE A REAL PROBLEM?

At least 30% of the world's potential crop production is lost each year because of the weather, pests anddiseases. Crop losses would be doubled if existing pesticide uses were abandoned. The world's problems andmalnutrition have not been solved, and the need for pesticides in maintaining food production is beyonddispute.

The question is 'Are we poisoning the very food crops which we are seeking to protect?' The short answer is'No'. Protecting crops from pests and diseases may leave minute amounts of pesticides on some foodstuffs.These 'residues', as they are called, are so small that they are difficult to appreciate. We are talking of theequivalent of measuring one second in three years, which requires very sophisticated techniques.

WHAT INDUSTRY DOES

Before selling a new pesticide, a manufacturer carries out many studies to show that if the product is sold,the recommended use will not harm the farmer or anyone who eats the treated food or the environmentoverall. These studies usually take about seven years and only one in 10-15 thousand chemicals testedreaches the market. Chemicals can fail because they are not effective enough, because they are expensive orbecause the pre-market testing shows that they are not safe enough. In studying pesticide residues in food,the manufacturer has to study two main aspects. First, what are the residues, where are they found and atwhat levels? Secondly, what is their significance?

The initial residue will be highest on those parts of the crop which are exposed to a spray. It will be lower onthose parts which are protected, as in the case of root vegetables. In fact, many pesticide uses do not leaveany detectable residues. The original deposit on a leaf or fruit will usually diminish with time, throughweathering or evaporation. It can also be changed chemically by the effects of sunlight or by enzymes withinthe plant.

The manufacturer has to understand all these factors thoroughly. Their importance differs with crop, witheach new pesticide and with different climatic conditions. The manufacturer also needs to study whathappens to the residues when the food is prepared for eating. Residues in bananas, for example, are mainlydiscarded with the skin but what happens to the residues in foods which are cooked (boiled, grilled or fried)?

These processes usually reduce the residues still further. Does pesticide use on animal feedstuffs lead toresidues in milk, meat and eggs? If so, what are the issues and at what levels are they present? These are alsofeatures which the manufacturer must consider, and may have to study. In practice pesticide residues infoods obtained from animals are invariably small.

Manufacturers study the possible consequences of these residues. Are they likely to harm man? Will theydamage the unborn child or have other effects upon reproductive processes? Could they induce cancers? Ormutations? The likely possibilities are investigated carefully and any chemical which is remotely dangerousis discarded. The intake of different foods varies between individuals within a community and betweenethnic groups, whether within a country or internationally. This has to be borne in mind when assessing thesafety of residues.

At the end of the day, the manufacturer has first to satisfy himself about the nature, extent and safety ofthese residues. He then has to satisfy governments, before the pesticide is marketed.

24 M. RICHARDSON

WHAT GOVERNMENTS DO

The checking does not stop at the efforts of the manufacturer. In many countries, governments regularlyanalyze foodstuffs for residues of pesticides. They study home-produced and imported foods, both raw foodsand food as prepared for eating. These studies are conducted independently of the efforts of the pesticidemanufacturers.

A survey which GIFAP has conducted on the results of such government analyses in Australia, Belgium,Canada, France, the Federal Republic of Germany, Ireland, Italy, The Netherlands, New Zealand, Sweden,Switzerland, UK and the USA is reassuring. Invariably, overall residues in food are much smaller in practicethan those predicted from the premarket testing, on which the safety evaluations are based. These residuelevels are well compatible with the safety limits set by competent health authorities, such as the acceptabledaily intakes set by the World Health Organization, which usually incorporate a safety factor of at least 100.

Why are residues so small? One reason is the concept of good agricultural practice. Even though a higherresidue level may be permissible on grounds of safety, a lower level is all that should be permitted if this canbe achieved routinely by the effective use of the product in the proper way and at the proper time. Farmershave an obligation to use a product in accordance with the label. Governments have a duty to providetraining and sound advice upon the need to spray and the range of products available.

Not all of a crop in anyone country is treated with anyone pesticide. Products are not always used at theirmaximum permitted rates or at the nearest permitted point to harvest. The dilution of treated with untreatedfood which occurs in commerce also contributes to the low levels of residues found in the diet. Mostcountries have legislation to control the safety of residues of pesticides in food.

In some countries the legislation is discretionary, in that public health analysts determine what residues arepresent and then exercise a judgment on their safety. In other countries, the legislation requires that a limit isestablished for residues of each product on each crop. Commodities failing to comply with that standard maybe deemed illegal, although that does not necessarily mean that they are unsafe.

OBSOLETE PESTICIDES

These present two problems: the first is continued use - which should be discontinued with all speed. Manyobsolete pesticides contain impurities/isomers which are at higher levels than normal and whose toxicitiesare invariably very much higher. Residues can also be greater and of greater persistence. The second majorproblem relates to obsolete pesticides disposal.

Obsolete pesticide use presents hazards in developing countries, but the disposal of these chemicals isequally hazardous. Over 30,000 tonnes/y of obsolete pesticides need to be disposed of by these countries butthe disposal costs are very high at $5000/tonne. According to the UN Food and Agriculture Organization,almost every country in Africa and the near East is affected.

Most products are categorized as obsolete because of inadequate storage and management practices, poorstock control, excessive donation from overseas, and because of forecast pest infestations which did notmaterialize. Almost 11,000 tonnes of obsolete pesticides and contaminants have been identified by FAO in65 countries including Gambia, Botswana, Cameroon, Madagascar, Morocco, Iraq, and Zaire. Disposal hastaken place in 22 countries (2 in the near East and 20 in Africa). FAO is now seeking assistance in thedisposal of remaining stocks.

The preferred method of disposal, incineration at an environmentally acceptable, dedicated plant, is notachievable in most African and near Eastern countries. Therefore, FAO provides assistance in shippingobsolete pesticides to Western countries with state-of-the-art incineration plants. This is costly, with anaverage disposal cost of $5000/tonne for pesticides which have to be shipped overseas. Disposal costs inAfrica alone are therefore in excess of $100 million.

Pesticides 25

There are several pilot disposal schemes underway. One example is the removal of about 48,000 Iitres ofdi(,~';.... {w,% M'ld'b.1,~·Ui '*~.;..~ <K'b.'l. ';'ffl.';'ffl.,'i'b."&.~ 'O~t'i'l.tw, Wj ~tIti~~ <:tltiY1t';~:a~ '4~ <ITL. nt't'tWpi,,!,countries must not only contend with the disposal of obsolete pesticides, they must also prevent the furtherbuildup of stock. Stocks of obsolete pesticides present difficulties for the public sector, includinggovernment organizations. The products are mostly leftovers that countries either bought or received asdonations. Included among the existing obsolete stocks are large volumes of organochlorines, such aslindane or dieldrin, which were retained as strategic stocks to control locust.

SUGGESTED RECOMMENDATIONS FOR THE FUTURE

I. Support via International Agencies, WHO, UNEP, FAO, etc. and respective Governments toestablish and strengthen legislation regarding all uses of pesticides.

2. To remove variations in legislative measures and regulatory standards.

3. Improve laboratory facilities especially at Customs to prevent importation of foods containingpesticides on the UN Banned & Severely Restricted List.

4. Legislate for strict penalties for internal manufacture (& importation) of such pesticides.

5. Ensure good access to data sources to enable risk assessments, management & risk reduction to beundertaken & to determine Average Daily Intakes (ADI).

6. Use of currently available substances to be prioritized.

7. Establish working group to provide data on ADIs, this group to include representatives fromgovernment industry, professional societies, and academics.

8. More use of natural pesticides, pheromones, bacteria, viruses,etc. should be advocated.

9. Greater awareness and openness in the community including the tourist industry to be advocated.

10. Pesticide practice in the Region should be harmonized.

ACKNOWLEDGMENT

This contribution has been adopted from Environmental Xenobiotics "Pesticides", Chapter 4 ofEnvironmental Xenobiotics. Mervyn Richardson (Ed), Taylor & Francis, London, 1996, pp. 47-71, and fromRisk Reduction: Chemicals and Energy into the 21st Century (Epilog). Mervyn Richardson (Ed.), and arereproduced with kind permission of the copyright holders Taylor & Francis, London, England.