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Persistence and Degradation of in Composting

Introduction objectionable compounds, even recalcitrant Composting is a process in which xenobiotics such as DDT, PCB and TCE. rapidly consume organic matter, using it as an · feedstock contains numerous and energy source and converting it into carbon diverse active microorganisms, all with their dioxide, water, microbial biomass, heat and own characteristics and capabilities. This compost. Feedstock used to fuel the composting diversity means a greater chance that a process may originate from a number of different will encounter a microbe that can sources, including yard trimmings, manure, degrade it. biosolids, and agricultural residues. These materials may contain a number of synthetic Mechanisms Affecting Pesticides organic compounds or xenobiotics, including During Composting pesticides. During composting, a pesticide may undergo the Many different physical and chemical factors help following physical and/or biological changes: determine the overall persistence of a pesticide. In Biological Degradation general, composting provides an optimal Microorganisms have developed many enzymes environment for pesticide destruction. This that can break down natural compounds. Modern publication discusses the potential for a pesticide scientists, though, have created pesticides with to become inactivated and degraded during chemical structures not found in nature. These composting. unique structures are often responsible for a The Composting Process pesticide's effectiveness and also explain why pesticides can persist in the environment. Compost is -suited for because: A pesticide's environmental persistence largely depends on its chemical structure and on the · The elevated or thermophilic temperatures presence of unusual functional groups, which are achieved during composting permit faster large sub-structures within the pesticide molecule. biochemical reactions than possible under The chemical structure helps determine its water ambient temperatures, accelerating pesticide solubility and consequently, its bioavailability, degradation. The high temperatures can also since microbes more readily assimilate water- make pesticides more bioavailable, increasing soluble compounds. the chance of microbial degradation. When a pesticide’s functional groups are attached · Some microorganisms may co-metabolize with weak or labile bonds, it can degrade more pesticides, where the microbes rely on the rapidly. Many modern pesticides have such bonds feedstock for and energy while breaking designed into them to avoid problems of extended down an adjacent pesticide. Co- persistence. Adding water may break many labile means that the does not bonds. This process is called hydrolysis and the receive any energy or potential food from the enzymes that promote hydrolysis are termed secondary reaction (in this case, from hydrolytic. is an example of an breaking down the pesticide). The many containing many such labile bonds that different organic matter structures in compost may be broken using hydrolytic enzymes (for help to promote co-metabolism of numerous example, esterase and phosphatase).

Note: Italicized words other than publications or scientific nomenclature are defined in the glossary.

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Other pesticides capable of hydrolytic degradation The hyphae release extracellular enzymes, which are: pesticides, urea derivatives, break down the pesticide and allow it to pass into , diazinon, dicamba, dichloropicolinic the cells. This allows the production of additional acid, dimethoate, phenylalkanoic ester, hyphae and/or energy. Although fungi are present dimethoate, phenylalkanoic pyrazon, , in compost feedstock, they contribute more to linuron, propanil, , and 2,4-D.Two other composting in its later stages. As exhaust classes of enzymes, mono- and di-oxygenases, the easily degraded organic matter from the are also commonly associated with pesticide feedstock, fungi then begin to degrade the more degradation. These enzymes introduce one or two recalcitrant polymeric organic matter. oxygen atoms, respectively, into the structure of a Intracellular Decomposition pesticide. This oxidation process often makes the After extracellular enzymes begin breaking down a pesticide more amenable to further degradation by pesticide or if it is otherwise bioavailable, a increasing its water solubility, thereby increasing pesticide may enter the cell of a microorganism. its bioavailability. Degradation may begin at the To pass into a cell efficiently, the pesticide must extracellular level and then proceed further at the be dissolved in water. Generally pesticides intracellular level. containing more oxygen, nitrogen, and tend Extracellular Decomposition to be more water soluble due to hydrogen Many of the same enzymes microorganisms use bonding. to break down cellulose, hemicellulose, and Once inside a cell, a pesticide may undergo lignin—the primary natural compounds in most varying degrees of degradation. Mineralization material—may also degrade pesticides reduces the pesticide to carbon dioxide, water, during composting. The large polymeric structure and other inorganic components. Typically, it of these natural compounds prevents their accounts for only a small portion of the passage into the microorganism for consumption. “disappearance” of a pesticide through To deal with this problem, microorganisms begin composting. breaking down chemicals outside their “body,” or extracellularly. They excrete enzymes out of their Water-insoluble pesticides tend to adsorb onto cells that react with the bonds in cellulose, and within organic matter, making them even less hemicellulose, and/or lignin, breaking them down bioavailable. The chemistry of the functional into smaller components. The shortened polymers groups in the pesticide and the organic matter can then be subjected to further degradation. dictates the strength of this pesticide-organic Extracellular enzymes can have very low matter interaction. “specificity,” working like a key that fits different Adsorbed pesticides are generally much more locks. They can, therefore, react with many resistant to breakdown than water-soluble different chemicals. If the enzyme finds a pesticide pesticides. This is because the latter have a much before reaching its “intended” substrate (for greater chance of contact with pesticide-degrading example, cellulose, hemicellulose, lignin), it may microorganisms as described above. react with it, changing the pesticide into a possibly Consequently, highly adsorbed pesticides are not less toxic and less hazardous form. Such co- considered bioavailable, enabling them to persist metabolism appears to play a significant role in for months or even years. However, when a degrading pesticides found in compost and . pesticide is adsorbed to organic matter that Fungi are the source of most extracellular eventually decomposes, it may once again enzymes. Some fungi often associated with become bioavailable. compost and soil organic matter are in the genera Additional factors can make adsorption a likely Trichoderma, Gliocladium, Penicillium, and outcome for even water-soluble pesticides. For Phanerochaete. Fungi grow through the example, many pesticides contain acidic and development of hyphae (long strings of cells) that nitrogen-containing functional groups that can extend throughout compost or soil organic matter. adsorb due to the presence of a negative or

3 positive charge, respectively. A negatively charged percentage of pesticide is typically lost to pesticide will adsorb to positively charged mineralization. functional groups on organic matter, while Besides mineralization, the “disappearance” of positively charged pesticides will adsorb to pesticides may occur by volatilization, adsorption, negatively charged functional groups on organic , or other methods noted earlier. A matter and clays. pesticide adsorbed to a compost molecule, while Volatilization technically present, may also be inactivated and Volatilization occurs when a pesticide partitions could permanently lose its control function. from the solid or aqueous phase to the gas phase. Many of the studies showed that concentrations of Once volatilized, a pesticide may diffuse into the and carbamate pesticides were atmosphere and either be destroyed or continue lower after composting. However, recalcitrant as an environmental risk. When mixing disturbs a organochlorine (for example, DDT) soil contaminated by a pesticide or other organic and pyridine carboxylic acid (for compound, a 30 percent or greater loss of the soil example, clopyralid and picloram) are more contaminant through volatilization is not unusual. resistant to degradation. Volatilization of a pesticide is highly temperature Lemmon and Pylypiw (1992) studied the dependent; thermophilic temperatures typically persistence of chlorpyrifos, diazinon, isofenphos, increase pesticide losses. The tendency for a and pendimethalin after composting with grass pesticide to volatilize also depends upon its size, clippings. The authors found the pesticides structure, and function. Moisture also affects undetectable shortly after application, and they volatilization rates. Water may physically impede disappeared quickly after composting. the flow of a gas phase pesticide by obstructing Vandervoort et al. (1997) showed a similar result: the pores through which gases travel. Water may decreasing concentrations of chlorpyrifos, 2,4-D, also promote volatilization by liberating weakly isoxaben, triclopyr, clopyralid, and fluprimidol after adsorbed pesticides. composting with grass clippings. Pesticide levels were below the routine detection limit after 128 Leaching days. They were typically lower in samples from Water-soluble pesticides have a tendency to be inside of compost piles that had been turned “rinsed away” through a process called leaching, versus the exterior and static piles. that is, the movement of a chemical within percolating water. Typically, leaching is of concern Muller and Korte (1975 and 1976) found that only when the pesticide moves into groundwater or 12 percent of the initial aldrin, 3 percent of the another location, posing an increased risk to , and less than 15 percent of humans and/or the environment. Many pesticides and imugan added to and are not highly soluble in water, readily adsorbing biosolids feedstock were degraded after onto the organic matter fraction. For this reason, composting. In contrast, 55 percent of the use of in agricultural tends to herbicides buturon and heptachlor were degraded. reduce the threat of pesticide leaching losses. Without any evidence for pesticide mineralization, the authors concluded that composting might not Case Studies be suitable for treating feedstock contaminated Many studies have been conducted on the fate of with these persistent pesticides. Critics of this pesticides during composting, some of which are study think the three-week period too short to summarized in an article in the Winter 2000 issue evaluate the potential for removal of persistent of Compost Science and Utilization. During pesticides. composting, pesticides will probably behave Racke and Frink (1989) also presented data on differently than they do when in soil. This is the limited mineralization of a pesticide during because of increased temperature, microbial composting. Approximately 97 percent of the diversity, microbial activity, and organic matter insecticide was transformed during during composting. While many of these studies composting of municipal biosolids, but only 5 showed a significant reduction in detectable percent of this could be attributed to pesticides, they also showed only a small

4 mineralization. Racke and Frink ended their occasions. In particular, after the inadvertent experiment after a short time (20 days), also composting of contaminated grassy material or drawing criticism. But both studies suggest that manure at two separate Washington composting appreciable mineralization of a pesticide during facilities, routine laboratory tests on the resulting composting may take more processing time. compost by the commercial composting facility did not indicate the presence of pesticides. Other studies focused on volatilization and Subsequent tomato damage first surfaced during mineralization in pesticide degradation. Petruska 2000 and prompted more sensitive laboratory et al. (1985) showed the importance of analysis of the compost that indicated 31–75 parts volatilization in the remediation of pesticide- per billion of clopyralid. Extensive testing of contaminated compost. Losses due to materials used to make the compost identified volatilization reached 22 percent for diazinon and clopyralid contaminated clippings from 50 percent for after three weeks of cow Spokane. Later that year another -laced manure and sawdust composting. Chlordane was compost was attributed to picloram contaminated not substantially mineralized, and diazinon was bedding and manure in Pullman. At the same considerably transformed, but again with a low location clopyralid contaminated hay and straw rate of mineralization. purchased for animal feed, and the resulting Rao et al. (1995) also found minimal manure was also composted during 2001. mineralization of the herbicide atrazine during Clopyralid is apparently more problematic than composting with several different wood-derived picloram since the different registered uses of the substrates. After 160 days of composting, there two pesticides suggest that materials typically was no detectable atrazine, yet a maximum of 7 coming into a composting facility are less likely to percent had been mineralized. The unmineralized be contaminated with picloram. As a minimum atrazine apparently leached or complexed with the precaution, operators should become familiar with humic components, preventing further the supplier and source of each material and transformation. inquire regarding persistent herbicide usage. While many of the studies have shown significant Bioassays by facility operators or highly sensitive decreases in detectable pesticides after analytical tests may be advisable on incoming composting, some of the pesticides were not materials and outgoing products. Washington completely degraded or mineralized. Instead, State University staff offers bioassay guidelines some were transformed to other chemical and color images of clopyralid-damaged at compounds, volatilized, adsorbed to the humic http://css.wsu.edu/compost/bioassay.htm. fraction, or leached out of the compost. The issue of pesticide after these types of changes is Growers and landscapers concerned about complex and varies significantly among pesticides. pesticide or herbicide residues may also wish to Some pesticides may increase in toxicity once take one or more precautionary measures before changed, while others may be inactivated. applying compost. A few herbicides are phytotoxic Additional studies are necessary to better below detectable analytical levels, so the above understand the fate of pesticides during bioassay guidelines may help assess the safety of composting. a compost pile. A simple seed germination test will ensure that a Possible Precautionary Measures split-sample of compost is mature and any Consumers and composters should note the present are not phytotoxic. The following Florida possibility that persistent pesticides can endure Web site includes guidelines for conducting seed the composting process at damaging levels. For germination tests: www.compostinfo.com/ example, as little as 10 parts per billion of tutorial/MaturityTests.htm. If either bioassay clopyralid can be toxic to legumes, potatoes, results in no germination or the young plants show sunflowers and tomatoes. symptoms of herbicide damage, it is advisable to Clopyralid and picloram are of concern because perform analytical tests on the remainder of the they have shown up in compost on at least two sample that include tests for suspected herbicides

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(parts per billion sensitivity), salinity, and compost Vandervoort, C., et al. “Fate of Selected Pesticides maturity. Users also can apply the compost in a Applied to Turfgrass: Effects of Composting on small test plot before covering an entire or Residues.” Bulletin of Environmental farm. Contamination and Toxicology, Vol. 58, No. 1, January 1997, pp. 38–45. Bibliography Buyuksonmez, F., et al. “Occurrence, Degradation Glossary and Fate of Pesticides During Composting. Part II: Active—Having the desired effect on the desired Occurrence and Fate of Pesticides in Compost . An active herbicide is one that is lethal and Composting Systems.” Compost Science & to the plant it was intended to kill. Utilization, Vol. 8, No. 1, Winter 2000, pp. 61–81. Adsorb (adsorption—The association and binding Bezdicek, D., et al. “Persistent Herbicides in of chemicals to the surface of solid particles such Compost.” BioCycle, Vol. 42, No. 7, July 2001, pp. as soil particles and organic matter. 25–30. Aqueous phase—Located in the water phase as Lemmon, C. R., and H. M. Pylypiw, Jr. opposed to the solid or vapor/gas phases. “Degradation of Diazinon, Chlorpyrifos, Isofenphos, and Pendimethalin in Grass and Bioavailable—Accessibility of a chemical to one or Compost.” Bulletin of Environmental many including plants, animals, and Contamination and Toxicology, Vol. 48, No. 3, microorganisms, enabling its degradation. March 1992, pp. 409–415. Clopyralid—The active ingredient in several Muller, W. P., and F. Korte. “Microbial Degradation herbicide products registered for use on , of Benzo-(a)-pyrene, Monolinuron, and Dieldrin in some or pasture (for example, Confront, Waste Composting.” Chemosphere, Vol. 4, No. 3, Curtail, Millenium, Stinger and Transline). 1975, pp. 195–198. Compost—A mixture of degradable and Muller, W.P., and F. Korte. “Ecological Chemical recalcitrant organic matter remaining after aerobic, Evaluation of Waste Treatment Procedures.” In F. thermophilic microbial decomposition and curing. Coulston and F. Korte (eds.), Environmental Curing—The final, mesophilic stage of Quality and Safety: Global Aspects of Chemistry, composting, following the thermophilic stage, Toxicology and as Applied to the where the more recalcitrant organic matter is Environment. New York: Academic Press, 1976, consumed. pp. 215–236. DDT—One of the world’s most widely used Petruska, J., et al. “A Benchtop System for pesticides. Banned in the and many Evaluation of Pesticide Disposal by Composting.” other industrialized countries since the 1970s. Nuclear and Management, Vol. 5, No. 3, 1985, pp. 177–182. Diffuse—To move away from a source, such as from a bag in water and smoke from a Racke, K. D., and C. R. Frink. “Fate of Organic cigarette in the air. Contaminants During Sludge Composting.” Bulletin of Environmental Enzyme—Commonly a protein that speeds up a Contamination and Toxicology, Vol. 42, No. 4, chemical reaction or reactions. April 1989, pp. 533. Feedstock—Starting materials to be composted. Rao, N., et al. “Mineralization of Atrazine During Functional group—One or more atoms that are Composting with Untreated and Retreated bound to a larger chemical. Lignocellulosic Substrates.” Compost Science and Utilization, Vol. 3, No. 3, Summer 1997, pp. 38– 46.

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Hydrogen bonding—Interaction between hydrogen Pores—Pockets of air of varying size within atoms of one chemical and the oxygen, nitrogen, compost and soils. Bulking agents such as wood or sulfur of another chemical. This interaction chips are often added to feedstock to increase the forms a common chemical bond called a hydrogen pore space, and thus the air content in the bond. This is commonly found in all of nature, compost. Increased air content allows for greater such as between water molecules and within DNA. microbial activity. Hydrolysis—The process of breaking weak Recalcitrant—Not easily broken down in nature. chemical bonds through the addition of water, Structure—The shape of an organic molecule is its usually involving hydrolytic enzymes. structure. Each organic chemical is made up of a Inactivated—Temporary or permanent loss of a number of building blocks that constitute a pesticide’s activity. molecule when fully assembled. Each organic molecule must contain carbon and may contain Labile—Easily degraded. any number of the following most commonly found Mesophilic—Temperature range of 50–105°F. atoms: hydrogen, oxygen, nitrogen, sulfur, and . Microbial biomass—The microbiological component of soil. TCE—Trichloroethene. An organic chemical that served as a in the dry-cleaning industry Microorganisms—Diverse groups of microscopic and for cleaning (usually military) aircraft. organisms including bacteria, fungi, , protozoa and . Thermophilic—Temperature range over 105°F. Mineralization—Breakdown of an organic Transformation—Chemical change ranging from compound into carbon dioxide, water, and other minor to complete destruction. inorganic components. Water solubility—Amount of a chemical dissolved Oxidation—Introduction of one or more oxygen in water. atoms into the structure of a chemical. Xenobiotic—Any synthetic chemical; literally Partition—Movement of a chemical from one meaning “foreign to life.” location to another, or from one state (gas, liquid, solid) to another. Principal Authors PCB—. An organic Andrew Singer, Lecturer, Department of chemical often associated with electrical Environmental Sciences, University of California, equipment such as capacitors and transformers. Riverside Persistence—Ability to remain in the environment David Crohn, Associate Professor, Department of after long periods of time. Environmental Sciences, University of California, Riverside Pesticide—Generic name for any chemical that kills or deters a pest, including plants and animals. Note: This fact sheet is intended to provide general information and point out issues to consider regarding composting. Picloram—The active ingredient in several Reference does not imply endorsement by the California Integrated Board. Updated in 2001 by herbicide products registered for use on rights of CIWMB staff to include information on clopyralid and picloram. way, fallow cropland or pasture (for example, CIWMB staff can be reached at (916) 341-6620. Grazon and Tordon). Polymeric—Term describing large molecules The energy challenge facing California is real. Every resulting from repeating molecules chemically Californian needs to take immediate action to reduce energy consumption. For a list of simple ways you can reduce bonded into large chains of varying lengths and demand and cut your energy costs, Flex Your Power and visit degrees of branching. Many synthetic chemicals www.consumerenergycenter.org/flex/index.html. such as are polymers.

Pub. #442-00-015 Revised April 2002 The California Integrated Waste Management Board (CIWMB) does not discriminate on the basis of disability in access to its programs. CIWMB publications are available in accessible formats upon request by calling the Public Affairs Office at 1-800-CA WASTE (in California) or (916) 341-6306. Persons with hearing impairments can reach the CIWMB through the California Relay Service, 1-800-735-2929. © Copyright 2000, 2002 by the California Integrated Waste Management Board. All rights reserved. This publication, or parts thereof, may not be reproduced without permission.