paper no. 3876 -...

The Environmental Fate of Oil and Gas Biocides: A Review

Terry M. Williams, Ph.D. Lisa E. Cooper, Ph.D.

Dow Microbial Control

The Dow Chemical Company 727 Norristown Road, PO Box 904

Spring House, Pennsylvania 19477-0904

ABSTRACT The environmental fate characteristics of industrial biocides used in oil and gas applications are of increasing concern due to the industry’s drive for sustainable best practices and regulatory pressure on water use and disposal. A detailed understanding of the environmental impact of biocides is critical to their safe use and requires extensive testing. This paper will review current data on the environmental fate and ecotoxicity of commonly used non-oxidizing and oxidizing biocides in oil and gas applications. The associated toxicity to non-target aquatic species and the ecotoxicity profiles for aquatic invertebrates, fish, and algae are presented. Environmental toxicity may be reduced or eliminated following degradation of the biocide active ingredients under environment conditions. Key elements of the environmental fate profile include biodegradability, bioaccumulation, end-product formation, and chemical stability (hydrolysis, photolysis). The specific pathways of biotic and abiotic decomposition and current methods for deactivation of the biocides are reviewed. Collectively, this information provides guidance on the selection and use of oil and gas biocides for various types of applications. Keywords: Biocide, environment, hydrolysis, half-life, biodegradation, photolysis.

INTRODUCTION Microbial contamination in oil and gas applications results in a variety of problems in drilling fluids, hydraulic fracturing fluids, water flooding, pipelines, and storage tanks. The primary microorganisms of concern are acid producing bacteria, sulfate (sulfur) reducing bacteria, and archaea. The key problems they cause are microbiologically influenced corrosion (MIC), souring (sulfide), pH drops, and biofouling (plugging).

1,2,3,4,5,6 Much work is currently being done to better define the microbial populations in oil

and gas applications under widely varying environmental conditions. Microbial control in the oil and gas industry has historically been achieved with a small number of biocides including glutaraldehyde, quaternary ammonium compounds (quats), cocodiamine,

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Paper No.

3876

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

tetrakishydroxymethylphosphonium chloride (THPS), and dibromonitrilopropionamide (DBNPA).7,8,9

More recently, additional non-oxidizing biocides (Dazomet and oxazolidines) as well as other oxidizing biocides (chlorine dioxide, hypochlorite, peracetic acid, and ozone) have also been employed in hydraulic fracturing. Biocide treatment programs are typically designed to provide optimal results based on environmental conditions, regulatory approvals, inherent efficacy, and cost. Understanding the environmental fate and ecotoxicology characteristics of industrial biocides is critical to their safe use for protection of the environment.

10 Regulatory requirements also impact the amount

of biocide that may be dosed by a specific product for a given application. A complete data package is required to adequately evaluate the potential impact of a biocide on the environment in order for an effective risk assessment to be completed. As with any compound, the relative risk is a function of the inherent toxicity of a compound and its exposure scenario during use. This paper will provide a review of the environmental fate and ecotoxicology characteristics of industrial biocides used in the oil and gas industry today. The studies include biological and chemical degradation, bioaccumulation, and end-product formation.

MATERIALS AND METHODS

Biocides The biocides and associated data sources / references reviewed in this paper are provided in Table 1. All biocide concentrations are reported on an active ingredient basis.

Table 1. Biocides reviewed and reference sources.

Common Name Chemical Name Reference Sources

Glutaraldehyde 1,5-pentanedial 11,12,13,14,15,16

THPS tetrakis(hydroxymethyl)phosphonium sulfate 17,18,19,20,21,22,23

ADBAC alkyldimethylbenzylammonium chloride 24,25,26

DDAC didecyldimethylammonium chloride 26,27,28

TTPC tributyl(tetradecyl)phosphonium chloride 29,30

Cocodiamine 1-(alkyl amino)-3-aminopropane diacetate 31

DBNPA 2,2-dibromo-3-nitrilopropionamide 32,33,34

Bronopol 2-bromo-2-nitro-1,3-propanediol 35,36,37

Dazomet tetrahydro-3,5-dimethyl-2H-1,3,5-thiadiazinethione 38,39,40,41

CMIT/MIT 5-chloro-2-methyl-4-isothiazolin-3-one +

2-methyl-4-isothiazolin-3-one 42,43,44

DMO 4,4-dimethyloxazolidine 45,46

CTAC 1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane

chloride 47,48

THNM tris(hydroxymethyl)nitromethane 49,50

Hypochlorite Sodium hypochlorite 51,52

Ozone Ozone 53,54

Chlorine dioxide Chlorine dioxide 55,56,57

Peracetic acid Peracetic acid 58,59

Environmental Partitioning Water solubility is determined in distilled water by measuring the active component in the liquid phase. Octanol-water partition coefficients are measured to determine the partitioning of biocides in an aqueous versus an organic phase. Biocides are added to mixtures of water and octanol and allowed to equilibrate into both phases. The logarithm of the concentration ratio in octanol to water (LogPow) is a

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relative measure of the hydrophobicity of the molecule. LogP values less than 3.0 are considered to show low potential of a compound to bioaccumulate in non-target organisms. Soil adsorption coefficients (Koc) are obtained by adding biocides to mixtures of soil and water and measuring the equilibrium concentration values in both phases. The Koc value, together with mobility studies that measure the movement of a biocide through a soil column with simulated rainwater or ground water can be used to assess the biocide’s migration potential. Bioaccumulation studies define the level of biocide and metabolites present in non-target aquatic organisms. The bioconcentration factor (BCF) is the ratio of the biocide plus residues recovered in biological tissues of test species relative to the concentration of biocide in solution. Values below 100 indicate low potential of a compound for bioaccumulation.

Physical-Chemical Degradation Hydrolysis studies are conducted in buffered water under varying pH and temperature conditions. Biocides are typically added at low levels, incubated in the dark, and analyzed periodically for active ingredient and metabolites.

60 Photolysis studies are conducted in buffered solutions and incubated in

natural or artificial sunlight and analyzed periodically for active ingredient and metabolites. Active ingredient and metabolites are measured over time by various methods.

Biological Degradation Studies Biodegradation studies were conducted to monitor the microbial degradation of biocides under environmental conditions. A range of methods have been proposed by the Organization of Economic Cooperation and Development (OECD 301 series) for determining “ready” biodegradation of compounds.

61,62 OECD 302 testing methods are also used to demonstrate the “inherent

biodegradability” of a compound. The methods are used where compounds do not pass the “ready” classification, but yet demonstrate a significant potential for degradation due to microbial attack.

Impact on Biological Waste Treatment Activated sludge respiration inhibition tests measure the effective concentration of biocide that reduces the respiration (oxygen consumption) rate of a microbial population in the sample by 50% (EC50). Tests are conducted using a range of concentrations to determine the required endpoints.

Major Pathways of Decomposition The major pathways of biocide degradation were determined by analyzing parent compounds and metabolites formed during hydrolysis, photolysis, and biodegradation studies. Metabolites may be identified using HPLC, GC-MS, LC-MS, and

14C radio labeling methods.

RESULTS AND DISCUSSION

Physical-Chemical Degradation Studies Hydrolysis studies were conducted to define the rate of degradation of dilute solutions of biocide in buffered aqueous media under varying pH conditions (Table 2). Results showed that nearly all biocides were most stable under slightly acidic conditions (pH 5) and stability was most reduced (shortest half-life) at pH 9. DBNPA, bronopol, and THPS were most sensitive to increasing alkaline pH. The shortest half-life among the biocides was observed with DBNPA at pH 9 (20 min half-life). Quats in general showed little change in stability from pH 5 to pH 9, consistent with the absence of functional groups susceptible to hydrolysis. As expected, the oxidizing biocides demonstrated the shortest half-lives with ozone being the most rapidly degraded at pH 7. Many of the biocides showed decreased stability due to photolysis as compared to hydrolysis (Table 2). Bronopol and dazomet had particularly short half-lives due to photolysis.

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Table 2. Half-life values for biocides as a function of hydrolysis and photolysis.

Biocide Hydrolysis at: Photolysis

pH 5 pH 7 pH 9

Glutaraldehyde 508 d 102 d 46 d 195 d

THPS 133 d 72 d 7 d 7 d

ADBAC 150-180 d 150-180 d 379 d Stable

DDAC 368 d 175-194 d 506 d Stable

TTPC nd nd nd nd

Cocodiamine Stable Stable Stable nd

DBNPA 66 d 20 h 20 min 6 d

Bronopol 5 y

(pH 4) 5 y

(pH 6) 120 d (pH 8)

1 d

Dazomet 6-10 h 2-4 h 1 h 4 h

CMIT/MIT >30 d >30 d 22 d 7 d

DMO rapid rapid rapid nd

CTAC 66 d 13 d 26 d 79-110 d

THNM >30 d 3.4 d 2.4 d 6 d

Hypochlorite nd >5 h nd 12 min

Ozone nd 20 min nd Unstable

Chlorine dioxide nd >6 h nd Unstable

Peracetic acid nd nd nd Unstable

d = day; h = hour; min = minute; y = year; nd = no data. Values for ~25-30° C Note: oxidizers tested in closed containers with no headspace (pH 7 data).

Environmental Partitioning The ultimate fate of organic compounds, including biocides, is related to their partitioning in environmental matrices. These can include water, soil, and sediment. A summary of the key partitioning parameters for each biocide is presented in Table 3. A major partitioning parameter is water solubility. All biocides showed relatively high water solubility values, compared to their typical use rates, as would be expected for compounds used in aqueous-based fluids for oil and gas applications. The lowest relative solubility of the non-oxidizers was with DBNPA and Dazomet. Ozone and chlorine dioxide showed very low solubility in water as well. The equilibrium concentration of molecules in water relative to an organic solvent (octanol) provides insight into how they partition between the aqueous and organic phases in environments containing hydrophobic organic material (e.g., petroleum hydrocarbon or fatty animal tissues). The parameter measured is the logarithm of the ratio of the concentration in the octanol phase to the water phase (LogPow). Compounds with LogPow values greater than 3.0 are considered to possess the potential to bioaccumulate in aquatic organisms. Most biocides showed low LogPow values indicating low potential for bioaccumulation in the environment. Bioconcentration factors (BCF) below 100 indicate no significant bioaccumulation potential. Results for measured and estimated BCF values of the biocides were generally low, indicating a low potential for bioaccumulation. Results of soil migration studies provide insight into how a biocide will partition in the environment between soil and water phases. Most biocides were considered mobile and would readily pass through soil columns, whereas cationic biocides and quats showed higher binding (less mobility) in soils, likely due to ion exchange interactions.

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Table 3. Environmental partitioning parameters for oil and gas biocides.

Biocide Water

Solubility

Log

POW

Bioconcentration

Factor (BCF)

Soil

Mobility

Glutaraldehyde 100% -0.33 <100 Mobile

THPS Miscible <0 <100 Mobile (est)

ADBAC Soluble <3 79 Non-mobile

DDAC Soluble nd 81 Non-mobile

TTPC Miscible nd nd Non-mobile (est)

Cocodiamine Soluble nd nd nd

DBNPA 1.24% 0.79 13 Mobile

Bronopol 28% -0.64 <100 (est) Mobile

Dazomet 0.36% <0.015 2 Mobile

CMIT/MIT >28% 0.4 5 Mobile

DMO 100% -0.08 <100 Mobile

CTAC >70% 1.25 2-40 Mobile

THNM Miscible -1.66 1 Mobile

Hypochlorite Complete -3.4 nd nd

Ozone 0.001% nd nd nd

Chlorine Dioxide (Chlorite)

0.8% (Complete)

nd (-7.2)

nd nd

Peracetic Acid Complete nd nd nd

nd = no data

Biological Degradation and Ecotoxicity of Industrial Biocides A variety of biodegradation studies may be used to classify a compound as “readily biodegradable.” These tests vary with the biodegradation endpoint that is measured. According to current OECD 301 test classification schemes, a compound may be considered “readily biodegraded” if the following occurs within 28 days: a) 70% removal of the dissolved organic carbon organic (DOC) from the compound; b) 60% conversion of the carbon in the molecule to carbon dioxide; or c) 60% oxygen consumption based on the theoretical oxygen demand of the molecule. The inoculum for the tests may include activated sludge, sewage effluent, surface waters and soil or mixtures. If a compound does not meet the criteria of “ready biodegradability,” then the “inherent biodegradability” for a compound can be assessed in the OECD 302 tests. “Inherent biodegradability” is defined as the potential of a compound to show biodegradation under favorable test conditions with more flexibility on the dosed concentration, time intervals, and microbial inoculum. If needed, a number of simulation tests are also available to assess the biodegradability of compounds in specific environments, such as wastewater treatment plants (OECD 303), soil (OECD 307), surface water (OECD 309), sediments (OECD 308), and seawater (OECD 306). A summary of the biodegradation results for the non-oxidizing biocides is shown in Table 4. Overall, glutaraldehyde, ADBAC, DDAC, DMO, and CTAC were the only biocides classified as “readily biodegradable” according to OECD guidelines. These biocides demonstrated rapid degradation of the parent compound and would not be expected to accumulate in the environment. All other biocides would be considered “inherently biodegradable” since they showed strong evidence of microbial degradation, but simply did not meet the strict criteria of the ready biodegradation tests. Technical literature for THPS described it as “readily biodegradable” using the U.S. EPA Guideline 40

CFR § 158 Subdivision N §162-4.17

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Table 4. Biodegradation classification for non-oxidizing biocides.

Active Ingredient OECD 301

“Ready”

OECD 302

“Inherent”

Reference

Source

Glutaraldehyde, ADBAC, DDAC,DMO, CTAC

+ + 12,13,23,28,45,47

DBNPA, THPS, bronopol, Dazomet, CMIT/MIT, THNM

- + 33,17,19,36,37,41,4

4,49

TTPC no data no data 29

+ = biocide meets pass criteria; - = biocide does not meet pass criteria

Most biocides have not been tested for inherent biodegradation in seawater (OECD 306). Glutaraldehyde and CTAC were the only biocides to show biodegradation under all three test methods. Traditional oxidizers are not classified as biodegradable since they are not organic compounds. Although peracetic acid is an organic oxidant, no data is available on its relative biodegradability.

Table 5. Ecotoxicology of oil and gas biocides.

Active Ingredient

Oral

LD50 (rat)

(mg/kg)

Dermal

LD50 (rat)

(mg/kg)

Daphnia

magna

(LC50 ppm)

Rainbow

Trout

(LC50 ppm)

Green Algae

(LC50 ppm /

EC50 ppm)

Glutaraldehyde 1,330 897-1,432 5 13 0.81

DBNPA 510 2,000 2.5 3.6 1.5

THPS 248-575 >2,000 15-19 94 – 119 0.2

Bronopol 180-400 64-160 1.4 26 0.05

Dazomet (MITC) 415 >2,000 11 16 1.1

CMIT/MIT 457 660 0.13 0.19 0.003-0.04

ADBAC 280-511 704-1,100 0.025 0.93 0.049

DDAC 450 4,300 0.06-0.94 2 0.02

TTPC 1,002 4,000 0.025 0.46 nd

Cocodiamine 2,000 2,000 0.045 0.16 0.0008

DMO 956-1,308 >2,000 48-51 93 4.2

CTAC 1,000 >5,000 26 64 0.8

THNM 1,875 >2,000 50-80 410 0.65

Hypochlorite 3-5 >10 0.07-0.70 0.07 0.10

Ozone nd nd 0.035 nd nd

Chlorine Dioxide (Chlorite)

39-113 (284)

nd (134)

nd (0.015)

nd nd

(1.3)

Peracetic Acid 50-500 >200 0.73 1.6 0.18

nd = no data

An assessment of the non-target mammalian and aquatic toxicity of the various oil and gas biocides is shown in Table 5. Oral and dermal toxicity values varied widely. Overall, oxidizers showed the highest degree of oral and dermal toxicity. Glutaraldehyde, TTPC, cocodiamine, DMO, CTAC, DMO, and THNM showed the lowest overall mammalian oral toxicity. Aquatic toxicity was assessed for the standard test species: Daphnia magna (water flea), fish, and green algae. Overall, the biocides with the highest toxicity to the aquatic organisms were the cationic

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quats (ADBAC, DDAC, TTPC, cocodiamine), oxidants (hypochlorite, ozone, chlorine dioxide), bronopol, and isothiazolone (CMIT). DMO, CTAC, and THNM showed the least overall aquatic toxicity.

Mechanisms and Major Pathways of Biocide Degradation Mechanism and Degradation of Glutaraldehyde. Glutaraldehyde is reactive with biological thiols and amines, which can deactivate or decompose the biocide. The efficacy of glutaraldehyde can be attributed to the positioning of two aldehyde moieties in one molecule at an ideal distance for forming stable structures upon encountering an amine. Aldehydes are highly reactive, electrophilic functional groups that are subject to attack by amines, sulfides, thiols, and other nucleophiles (Figure 1). The resulting byproducts do not possess antimicrobial activity. These are discussed in more detail elsewhere.

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In bulk storage, glutaraldehyde can polymerize irreversibly due to elevated pH or contamination with an amine product. Under acidic conditions and at use concentrations, polymerization is generally not an issue. Intentional deactivation of glutaraldehyde at use concentrations is achieved in one of two ways: 1) by treatment with base (alkali); or 2) by treatment with sodium bisulfite.

Figure 1. Reactivity of glutaraldehyde with various nucleophiles. Aerobic biodegradation of glutaraldehyde involves oxidation of both aldehyde groups to the corresponding carboxylic acid, glutaric acid, as the initial primary metabolite (Figure 2). Glutaric acid is then further mineralized to CO2 as the final end product. Under anaerobic conditions, glutaraldehyde is transformed initially to hydroxypentanal and further metabolized to the di-alcohol, pentanediol. The rapid biodegradation of glutaraldehyde is demonstrated in the short half-life under aerobic and anaerobic conditions (12 and 8 hours, respectively). Glutaraldehyde was shown to be readily biodegraded, according to the OECD 301A method.

13 Greater

than 70% of the glutaraldehyde compound was degraded by microorganisms within 10 days in this test and 83% degraded after 28 days. Additional studies, showed similar results (78% degraded after 28 days) when using seawater as the source of microorganisms and measuring oxygen consumption to demonstrate biodegradation potential.

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Degradation of THPS. THPS is considered a chemical precursor to the active biocidal compound tris(hydroxymethyl)phosphine (THP). The two chemical species are in equilibrium with one another and are converted via hydrolysis of a hydroxymethyl group from the phosphorus center. The resulting phosphine is a reducing agent that disrupts biological disulfide bonds (Figure 3).

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Figure 2. Aerobic (scheme 1) and anaerobic (scheme 2) biodegradation pathways for glutaraldehyde.

Figure 3. Reaction of THPS with thiols.

THPS has been reported to undergo rapid microbial degradation according to EPA guidelines and be considered as “readily biodegradable” with 70-80% converted to CO2 under aerobic (21 days) and anaerobic conditions (365 days), respectively.

22 Tris(hydroxymethyl)phosphine oxide (THPO), which

has low toxicity, is a key degradation product. Degradation of DBNPA. DBNPA contains two reactive bromine substituents that react with cellular amines, thiols, and other nucleophiles located within biological materials. These materials are likely responsible for the rapid degradation of DBNPA in the environment and play a role in the rapid speed of kill of this biocide. DBNPA reacts with microbial cells by oxidizing cellular thiols to disulfides and beyond (Figure 4), resulting in loss of the organic-bound bromine as bromide. DBNPA is faster-acting at higher pH, but also undergoes faster degradation with increased pH. Hydrolysis rates and degradation pathways are discussed in more detail elsewhere.

65 Although DBNPA does have a weak

oxidizing potential, it does not form HOBr in solution and does not react with the free chlorine test method. Biodegradation of DBNPA has also been demonstrated in several systems. OECD 301B studies measuring

14CO2 released from uniformly labeled DBNPA (0.06 ppm) showed 78% of the organic

carbon was converted to CO2 within 28 days.32

Though extensive biodegradation was observed, the compound did not meet the strict criteria of “readily biodegradable” since 58% of the carbon was released as CO2 within the 10-day window, just short of the 60% required. Additional studies showed

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83% degradation using the OECD 303A test. Overall, it is clear that DBNPA is metabolized to a very high degree under relevant environmental conditions.

Figure 4. Reaction of DBNPA with cellular thiols.

Degradation of Bronopol. As seen with the other biocides, bronopol is also reactive with thiol compounds. It functions as a biocide by oxidizing thiols on cell and protein surfaces. Studies have shown it acts as a catalytic oxidant in the presence of air as the bulk oxidant (Figure 5) and is an agent capable of stoichiometrically degrading cysteine or glutathione in the absence of oxygen.

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Figure 5. Reaction of bronopol with thiols and oxygen. Bronopol has also been shown to undergo significant biodegradation with 51-57% of the organic carbon released as CO2 according to the OECD 301B protocol. Although bronopol did not meet the “ready biodegradability” criteria, it was clearly metabolized to a significant degree by microorganisms under environmental conditions. Degradation of Isothiazolone Biocides. Biological degradation of methyl-isothiazolones proceeds via ring-opening of the molecules at the nitrogen-sulfur bond, followed by loss of chloride and sulfur. The major initial organic byproduct identified for CMIT and MIT was methyl malonamic acid, which was further metabolized to malonamic acid, methyl amine, and ultimately carbon dioxide. Additional information on the biodegradation of isothiazolones is presented elsewhere.

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Isothiazolones are also susceptible to nucleophilic attack by materials such as sulfide, bisulfite, mercaptans, organic thiols (cysteine), and amines. Similar to microbially mediated decomposition, degradation by nucleophiles involves cleavage of the isothiazolone ring and formation of disulfide species. The rate of reaction was strongly influenced by environmental conditions (pH and temperature) and reactant concentration. Once the isothiazolone ring is opened the biocide is inactivated. Although CMIT and MIT showed significant microbial attack and conversion to CO2 (>50%), they did not meet the “ready biodegradability” criteria. However, these biocides are clearly metabolized to a significant degree by microorganisms under environmental conditions.

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Degradation of Miscellaneous Biocides Although summary information (endpoints) on biodegradation of the remaining non-oxidizing biocides was available on material safety data sheets and EPA documents, no additional details on the extent of degradation or endproducts were available for the remaining biocides.

Impact of Biocides on Biological Waste Treatment The effect of biocides on inhibition of respiration (oxygen uptake) by activated sludge microorganisms is one of the typical studies conducted for registration of biocides. This measurement provides information on the concentration of the biocide that may potentially impact the operation of biological waste treatment processes. Results for the various biocides (typically included in MSDS or product bulletins) are provided in Table 6. In most cases, these studies were conducted using native populations of activated sludge, so there was no pre-acclimation or adaptation of the microbes to the biocides, which present a worst-case scenario for this type of assessment.

Table 6. Toxicity values for non-oxidizing biocides on activated sludge metabolism.

Biocide

Activated Sludge

Respiration Inhibition

EC50

Glutaraldehyde >50 ppm

DBNPA 3 ppm

Bronopol 43 ppm

THPS 24 ppm

Dazomet 17 ppm

CMIT/MIT 5 ppm

ADBAC 8 ppm

DDAC 11 ppm

TTPC nd

Cocodiamine nd

DMO 107 ppm

CTAC 1,504 ppm

THNM 629 ppm

nd = no data For most of the biocides, the EC50 (effective concentration for 50% inhibition) values are in the single-digit to low double-digit ppm range. CMIT/MIT and DBNPA showed the most significant inhibition. DMO, CTAC, and THNM all showed the lowest toxicity to the activated sludge process (highest EC50 values). As a result, even modest (10-100x) dilutions of these biocides into wastewater systems will have little to no observable impact on the efficiency of the biological treatment processes. No similar data were available for the oxidizing biocides.

Deactivation of Industrial Biocides In some cases, industrial biocides may need to be deactivated prior to discharge to wastewater treatment system or to natural waters. There are many approaches available to safely and effectively deactivate (neutralize) the various biocides used in oil and gas applications. Reduced sulfur compounds, such as bisulfite or metabisulfite may be used to deactivate glutaraldehyde, DBNPA,

THPS, bronopol, CMIT/MIT, DMO and all oxidizers.63

Quats are typically deactivated using clay,

anionics, or diatomaceous earth.

North Sea Rating System – Offshore Chemical Risk Assessment The Offshore Chemical Notification Scheme (OCS) applies to all chemicals that are used in the exploration and offshore processing of petroleum on the UK Continental Shelf. This system uses a risk assessment model, based on biodegradation, bioaccumulation and aquatic ecotoxicity, to rate the

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various chemicals used in the offshore industry. The risk assessment calculated a Hazard Quotient based on the ratio of the predicted concentration in the environment to the predicted no-effect concentration derived from aquatic toxicity testing. A color scheme is then used to rate the compounds based on relative risk to the environment.

67 The rating scale (from lowest hazard to highest hazard) is:

Gold > Silver > White > Blue > Orange > Purple. The current ratings (April 2013) for the oil and gas biocides discussed in this paper are provided below (Table 7). The highest rated biocides for the offshore oil and gas applications are glutaraldehyde, THPS, DBNPA, DMO (oxazolidine), and DDAC quat. Bronopol was rated as White for some applications. Biocides that had previously been on the list but have been recently removed (de-listed) include ADBAC, TTPC, and Dazomet.

Table 7. Summary of UK North Sea ratings for oil and gas biocides.

Biocide North Sea

Color Rating

DMO Gold

Glutaraldehyde, DBNPA, THPS, DDAC Gold-Silver

Bronopol White

Dazomet, ADBAC, TTPC De-Listed

CMIT/MIT, CTAC, THNM, cocodiamine no data

Rating scale: Gold > Silver > White > Blue > Orange > Purple

SUMMARY AND CONCLUSIONS Oil and gas applications require a high degree of microbial control to prevent unwanted problems such as microbiologically influenced corrosion, souring, and plugging. The use of industrial biocides to prevent or reduce microbial growth provides a risk for exposure to both humans and the environment. The risk is effectively managed with the appropriate safety protocols, handling procedures, and dosing technologies. In order to better assess the potential impact of unwanted discharge of industrial biocides or other chemicals to the environment, it is imperative to have a detailed understanding of their ecotoxicity properties to non-target organisms and their ultimate environmental fate. Industrial biocides are rapidly degraded in environmental systems by a variety of mechanisms, including hydrolysis, reactions with nucleophiles, photolysis, and biodegradation. The resulting half-lives of the compounds in environmental systems are typically short and their decomposition yields degradation products including CO2 and less toxic metabolites. Biodegradation is a critical mechanism for decomposition of industrial biocides in the environment. Glutaraldehyde, ADBAC, DDAC, DMO, and CTAC were the only biocides classified as “readily biodegradable” according to stringent OECD guidelines. The remaining organic biocides typically demonstrated substantial biodegradation in standard testing, but not at a level sufficient to be classified as “readily biodegradable.” Hydrolysis rates were rapid with all of the oxidizers, but some variation was seen. DBNPA was the least stable and quats were the most stable in water. The effect of biocides on non-target organisms is also critical to understand. The highest toxicity to the non-target aquatic organisms occurred with the cationic quats (ADBAC, DDAC, TTPC, cocodiamine), oxidants (hypochlorite, ozone, chlorine dioxide), bronopol, and isothiazolone (CMIT). DMO, CTAC, and THNM showed the least overall aquatic toxicity to standard test species (i.e., water flea, fish, and algae). With many biocides, the concerns of aquatic toxicity are mitigated by rapid degradation of the biocides following use, thus risks to the environment are minimized. For mammalian toxicity, the oxidizers showed the highest degree of oral and dermal toxicity. Glutaraldehyde, TTPC, cocodiamine, CTAC, DMO, and THNM had the lowest overall mammalian oral toxicity.

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The selection and use of oil and gas biocides is based on many aspects, including performance, cost, safety, and environmental properties. With growing concerns for the environmental impact of hydrocarbon recovery processes, operators and service companies have many environmentally sustainable microbial control programs available. Preferred biocides have effective performance, lower overall toxicity, a high degree of biodegradability, and low environmental persistence resulting in a favorable environmental profile. Should the need arise to deactivate these biocides prior to discharge, there are readily available and effective methods to chemically degrade these compounds to further minimize any potential adverse environmental effects and meet required discharge regulations.

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Company. 2007 14. The biodegradation of glutaraldehyde in seawater. Oilfield Bugbusters – Technical Bulletin. The Dow Chemical Company. 2003 15. AQUCAR GA 50 Water Treatment Microbicide for Use in Industrial Water Treatment, Papermaking, and Gas and Oilfield Systems. Technical Bulletin. Dow Chemical Company. 2010 16. Product Safety Assessment: Glutaraldehyde. The Dow Chemical Company. 2009.

17. Rhodia technical bulletin – TOLCIDEt PS. 2002.

18. Tetrakis(hydroxymethyl)phosphonium sulfate Chemistry Document. US EPA. EPA-HQ-OPP-2011-0067. 2011. 19. Registration review document: Product chemistry, environmental fate and ecological effects summary for tetrakis(hydroxymethyl)phosphonium sulfate. US EPA Memorandum. 01/24/2011 20. Tetrakis(hydroxymethyl)phosphonium sulfate (THPS) Summary Document: Registration Review. US EPA EPA-HQ-OPP-2011-0067. March 2011. 21. AQUCAR THPS 75 Water Treatment Microbicide. Material Safety Data Sheet. Dow Chemical Company. 2010. 22. Health Canada. Evaluation report for tetrakis (hydroxymethyl) phosphonium sulfate. ER-2010-02. 23. TOLCIDE PS75 Material Safety Data Sheet. Rhodia. 2007. 24. Reregistration eligibility decision for Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC). US EPA Report 739-R-06-009. 2006.

25. BARQUATt DM-50 Safety Data Sheet. Version:28.11.2006/EN. Lonza. 2006.

26. Directory of Microbicides for the Protection of Materials a Handbook, ed. W. Paulus. Netherlands: Springer. 2005 27. Reregistration eligibility decision for Aliphatic Alkyl Quaternaries (DDAC). US EPA Report 739-R-06-008. 2006.

28. Bardact 2250 Material Safety Data Sheet. Version 1.13. Lonza. 2010.

29. Bellacidet 350 Material Safety Data Sheet. SDS No. 10794. BWA Water Additives. 2008.

___________________________

t Trade names. AQUCAR is a registered trademark of Dow Chemical Company. TOLCIDE is a

registered trademark of Rhodia. BARDAC and BARQUAT are registered trademarks of Lonza, Inc. BELLACIDE is a registered trademark of BWA Water Additives. 30. Bellacide 355 Material Safety Data Sheet. SDS No. 110723. BWA Water Additives. 2007.

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31. Reregistration eligibility decision for Alkyltrimethylenediamines (Case 3014). US EPA Report 739-R-07-004. 2007 32. AQUCAR DBNPA 20 Water Treatment Microbicide Materials Safety Data Sheet. Dow Chemical Company. 2009 33. DBNPA 100 PTECH. Water Treatment Microbicide Materials Safety Data Sheet. Dow Chemical Company. 2007. 34. Reregistration eligibility decision 2,2-dibromo-3-nitrilopropionamide. US EPA 738-R-94-026. 1994. 35. Reregistration Eligibility Decision for Bronopol. US EPA 738-F-95-029. 1995.

36. Materials Safety Data Sheet for BIOBANt BP 30 Preservative. Dow Chemical Company. 2009. 37. Bronopol Technical Bulletin. OSP Microtech Inc. http://www.ospmicrocheck.com/Products/TechnicalData/ bronopol-physical.htm 38. Revised environmental fate and ecological assessment for the registration of Dazomet. US EPA. 2008. 39. Reregistration eligibility decision (RED) for Dazomet. US EPA Report No.738-R-08-007. 2008. 40. Directive 98/8/EC concerning the placement of biocidal product on the market. Assessment report: Dazomet. March 2010.

41. Protectolt and Myacidet Dazomet Products Technical Information. BASF, 2006. 42. T.M. Williams, A.H. Jacobson. Environmental Fate of Isothiazolone Biocides. CORROSION/99, paper no. 99-303, Houston, TX: NACE International, 1998. 43. Reregistration eligibility decision for methylisothiazolone. US EPA No. EPA738-R-98-012. 1998.

44. KATHONt WT Material Safety Data Sheet. Dow Chemical. 2011. 45. BIOBAN CS-1135 Antimicrobial Material Safety Data Sheet. Dow Chemical Company. 2009 46. Product Safety Assessment: BIOBAN CS-1135 Antimicrobial. Dow Chemical Company. 2011. 47. AQUCAR TA 64 Water Treatment Microbicide. Material Safety Data Sheet. Dow Chemical Company. 2011. 48. Registration eligibility decision (RED) for DOWICILt CTAC. USEPA No. EPA 738-R-95-017. 1995. ______________________________

t Trade names. BIOBAN, KATHON, and DOWICIL are registered trademarks of Dow Chemical

Company. PROTECTOL and MYACIDE are registered trademarks of BASF.

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49. AQUCAR TN50 Water Treatment Microbicide Material Safety Data Sheet. Dow Chemical Company. 2011. 50. Summary of product chemistry, environmental fate, and ecotoxicity data for the 2-(hydroxymethyl)-2-nitro-1,3-propanediol registration review document. US EPA. 2009. 51. Sodium hypochlorite solution Material Safety Data Sheet. ERCO Worldwide. Revision #3, 2012. 52. HASA 12.5% Sodium Hypochlorite Solution Material Safety Data Sheet. HASA Inc. 2011. 53. Ozone Material Safety Data Sheet. BOC Gases. The BOC Group, Inc. 2000. 54. Ozone from Air. Material Safety Data Sheet. P-6219-A. Praxair-Traligaz Ozone Company. 2000.

55. Chlorine Dioxide Solution – SVPt-PURE. Safety Data Sheet. Version 15. EKA Chemicals Inc. 2008.

56. ADOXt 3875 Material Safety Data Sheet. DuPont Chemical Company. Version #2. 2011. 57. Sodium Chlorite 31% Solution. Material Safety Data Sheet. Arkema Canada Inc. 2010. 58. 15% Peracetic Acid. Material Safety Data Sheet. FMC Corporation. Revision # 15. 2009. 59. EPA RED Facts for Peroxy Compounds. US EPA Report No. 738-F-93-026. 1993. 60. U.S. Environmental Protection Agency, Pesticide Assessment Guidelines, Subdivision N-Chemistry: Environmental Fate (Washington D.C.; USEPA, 1982). 61. OECD Guideline for Testing of Chemicals. www.oecd.org/dataoecd/ 17/16/1948209.pdf. 1992. 62. Introduction to the OECD Guidelines for Testing of Chemicals Section 3. http://www.oecd.org 63. Williams, T.M. and H.McGinley. Deactivation of industrial biocides. In: Proceedings of CORROSION/2010. Paper no. 09059. National Association of Corrosion Engineers. Houston, TX. 2010. 64. The biodegradation of glutaraldehyde in seawater. Oilfield Bugbusters – Technical Bulletin. The Dow Chemical Company. 2003. 65. Exner, J.H., Burk, G.A. and Kyriacou, D. Rates and Products of Decomposition of 2,2-Dibromo-3-nitrilopropionamide. J. Agr. Food Chem., 21(5), pp. 838-842. 1973. 66. Shepherd, J.A., Waigh, R.D., and Gilbert, P. Antibacterial Action of 2-Bromo-2-Nitropropane-1,3-Diol (Bronopol), Antimicrobial Agents and Chemotherapy, 32(11): 1693-1698. 1988. 67. http://www.cefas.defra.gov.uk/industry-information/offshore-chemical-notification-scheme/about-ocns.aspx ______________________________

t Trade names. ADOX is a registered trademark of EI DuPont de Nemours. SVP-PURE is a registered

trademark of Eka Chemicals Inc.

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