CHAPTER 13 Environmental Fate of Pesticides Masako Ueji and Yuso Kobara CONTENTS Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 Pesticides in Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 Behavior in Soil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 Residue in Soil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 Adsorption and Leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 Degradation in Soil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Pesticides in Aquatic Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 Runoff from Farmland to Aquatic Environment . . . . . . . . . . . . . . . . 280 Degradation in Aqueous Environment. . . . . . . . . . . . . . . . . . . . . . . . 283 Pesticides in the Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 Entry Pathways into the Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . 285 Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 Wind Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 Volatilization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 Behavior of Pesticides in the Atmosphere . . . . . . . . . . . . . . . . . . . . . 287 Deposition of Pesticides with Rainfall and as Dust. . . . . . . . . . . . . . 287 Degradation of Pesticides in the Atmosphere . . . . . . . . . . . . . . . . . . 287 Influences of Pesticides on Organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 Impacts on Nontarget Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 Bioconcentration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 275 0-8493-0904-2/01/$0.00+$.50 © 2001 by CRC Press LLC 920103_CRC20_0904_CH13 1/13/01 11:10 AM Page 275 276 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT INTRODUCTION Pesticides play a major role in controlling insect pests and weeds and have brought about sustained high yields and higher quality of agricultural produce. They have also helped liberate farmers from the backbreaking task of weeding. Pesticides, which serve purposes including those of insecticides, fungicides, and herbicides, are active substances that have some sort of toxi- city toward living things. Pesticides applied to farmland are put into the environment on purpose then are dispersed widely throughout the atmos- phere, soil, and aquatic environment outside farmland. Thus, in an attempt to solve problems involving toxicity, residual tendency, and selectivity among organisms, which are drawbacks of pesticides, improvements have been made in the chemical structures of these chemicals and in the ways they are formulated and applied. As a result, currently used pesticides are com- pounds characterized by low toxicity, easy degradability, high selectivity, and high activity (Takagi and Ueji, 1997). Decreasing the environmental load caused by pesticides is also needed to further expedite ecological farming practices. The environmental fate of pesticides (i.e., their dispersion, movement, adsorption, desorption and degradation in soil, aquatic environment, and the atmosphere, as well as their effects on organisms in the environment) changes greatly depending on environmental factors, such as meteorological conditions, soil condition, and properties of organisms, in addition to the physicochemical characteristics of pesticides, the manner of their formula- tion, and how they are used. In the environment and in the metabolic processes of organisms, pesticides are generally detoxified, but in some instances they are transformed into metabolites that are even more toxic. This makes it vital to ascertain metabolic pathways and the characteristics of metabolites. PESTICIDES IN SOIL Behavior in Soil After application, pesticides disperse into the atmosphere and aquatic environment and adhere to plants, but with the passage of time much of the applied amount settles onto soil surfaces, which is why research into the fate of these chemicals in soil has had priority. The pesticides in soil disappear with time and each process is influenced by various factors. In the first stage, (1) pesticides disperse into the atmos- phere from the soil surface due to transpiration occurring immediately after application, resulting in rapid disappearance. Transpiration is governed largely by the vapor pressure created by the chemicals, the method of use, meteorological conditions such as temperature and wind velocity, and soil 920103_CRC20_0904_CH13 1/13/01 11:10 AM Page 276 ENVIRONMENTAL FATE OF PESTICIDES 277 factors such as soil moisture content and the amount of organic matter. This is followed by (2) runoff into the aquatic environment, degradation on the soil surface by sunlight, penetration and leaching into soil, and adsorption by soil particles. The latter stage processes are influenced by water solubility and susceptibility to photolysis of pesticides, soil characteristics including type and structure of soil, clay content and the amount of organic matter, and meteorological conditions such as rainfall. The second stage of the disappearance process is degradation reactions, which proceed at a more leisurely pace than the first stage. While reactions such as chemical hydrolysis occur here, this stage consists mainly of biodegradation involving soil microorganisms. Moreover, calculated regres- sions show good agreement with a logarithmic disappearance of pesticides (Edwards, 1966). Pesticide fate in soil can be roughly summarized in the following manner. 1. The greater a chemical’s vapor pressure, the more it disperses into the atmosphere from the soil surface (Swann et al., 1982). 2. The greater a chemical’s water solubility, the greater its runoff with surface water and the more it penetrates into the soil (Weber, 1994). 3. The more organic matter in soil, the more readily chemicals are adsorbed, hence moving with greater difficulty (McEwen and Stephenson, 1979). 4. Degradation in soil is almost totally biodegradation. Pesticides thus disappear quickly in soil with high microbial activity (Weed and Weber, 1974; Scheunert, 1992). Residue in Soil The residue of pesticides in soil depends greatly on characteristics of pes- ticides and the soil, meteorological conditions, and other factors. A look at pesticides by type shows that the organochlorine chemicals such as DDT, BHC, and aldrin and dieldrin are especially stable in soil and remain for a long time. Half-life (the time required for half of the applied pesticide to dis- appear) is used as an indicator of residual tendency. As shown by the half- lives of various pesticides determined in laboratory testing and listed in Table 13.1, many of the chemicals in current use have short residual times (Hamaker, 1972; Kanazawa,1992). Comparing the disappearance times of dif- ferent pesticides shows that the organophosphates disappear quickly, while the carbamates have comparatively long residual times. Fungicides generally disappear quickly. On the other hand, herbicides generally have long half- lives, with some persisting as long as several months. The reason for this is that herbicides must have persistence because weed seeds germinate over a long period of time. 920103_CRC20_0904_CH13 1/13/01 11:10 AM Page 277 278 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Table 13.1 Half-lives of Pesticides in Upland Soil (A) (B) (C) (D) alloxydim(H) alachlor(H) benomyl(F) BHC(I) bensultap(I) captan(F) benthiocarb(H) bromacil(H) carbaryl(I) carbofuran(I) cypermethrin(I) DDT(I) chlorfenvinphos(I) cyanofenphos(I) dicofol(I) dieldrin(I) diazinon(I) dalapon(H) dimethirimol(F) dichlobenil(H) diflubenzuron(I) dimethoate(I) endosulfan(I) flutolanil(F) dithianon(F) 2,4-D(H) fenvalerate(I) imazapyr(H) fenthion(I) ethofenrpox(I) guazatin(F) metribuzin(H) glufosinate(H) fenothiocarb(I) imazali(F) myclobutanil(F) ioxynil(H) glyphosate(H) iprodione(F) myclobutanil(F) malathion(I) meneb(F) lepthophos(I) oxyfluorofen(H) mecarbam(I) methyl dymron(H) linuron(H) paraquat(H) methidathion(I) oxamyl(I) matalaxyl(H) simazine(H) methomyl(I) phosmet(I) metolachlor(H) tebuthiuron(H) monocrotophos(I) propaphos(I) oxadiazin(H) thiazafluron(H) permethrin(I) propineb(F) pencycuron(F) triadimeforn(F) parathion(I) pyridaphenthion(I) prometryne(H) propanil(H) thiram(F) pyrzophos(F) tetrachlorvimphos(I) trifluralin(H) terbacil(H) trichlorfron(I) zineb(F) tetradifon(I) vamidothion(I) triadimenol(F) Half-lives in soil: (A) Ͻ14 days; (B) 15–42 days; (C) 43–180 days; (D) Ͼ180 days (I): Insecticides; (F): Fungicides; (H): Herbicides Adsorption and Leaching Most of the pesticides that fall to the ground are adsorbed by the upper portion of the soil and held there. Subsequently they are desorbed from the soil particles, move, and disperse through the soil with soil moisture, or they degrade and disappear. The time needed for pesticides to disappear com- pletely from soil varies considerably depending on soil conditions and the physicochemical characteristics of the chemicals. Generally, the more firmly a chemical adsorbs into soil, the less easily it moves. Some of the soil adsorption mechanisms of pesticides are by van der Waals force, hydrogen bonding, covalent bonding, and ion exchange. They differ depending on the combination of a pesticide’s chemical structure and the soil’s components. Of these, the primary mechanism of adsorption reac- tions is cation exchange with the negative charge of the soil surface. Adsorption is strongest, for example, in the herbicide paraquat and diquat, which has quaternary amines containing the bipyridinium cation, because 920103_CRC20_0904_CH13 1/13/01 11:10 AM Page 278 ENVIRONMENTAL FATE OF PESTICIDES 279 these are absorbed firmly the moment they make contact with the soil (Hayers et al., 1975). Also readily adsorbed are urea derivatives, the triazines and the carbamates, etc., whose molecules contain cationic NH groups (Wauchope and Koskinen, 1983). And as with amino products formed by the reduction of nitro groups that replace benzene rings, when degradation products with structures making them easily adsorbed are formed in the soil, the result is stable bonding (Nash, 1988). Some soil factors are organic matter content, types of clay minerals, clay content, and aggregate structure. Many different interactions occur between these factors and pesticides’ chemical structures. In many instances organic matter content has the biggest effect. In particular, the higher the soil’s humic acid content, the stronger its adsorption is; likewise, adsorption is strong in soils with high clay content and 2:1 clay minerals, such as vermiculite and montmorillonite. As with chemical substances in general, the strength or weakness of pesticide soil adsorption is indicated by the soil sorption coeffi- cient, Kd, (McCall et al., 1976). Kd is the value obtained by agitation mixing of a chemical substance dissolved in water with soil, noting the concentration of the chemical in soil when an adsorption equilibrium has been attained, and dividing that by the concentration in water. Further, adsorption depends primarily on the amount of organic matter in the soil. For that reason, Kd is indicated by the soil sorption equilibrium constant (Koc), calculated accord- ing to the organic carbon content of the soil and used as the mutual soil sorp- tion of chemical substances (Weber, 1995). With regard to pesticides as well, the larger Koc is, the more easily a chemical is adsorbed by the soil, and the less it moves through the soil. On the other hand, highly water-soluble pesticides could cause ground- water contamination (discussed below) in sandy soil with little clay or organic matter, or when soil moisture increases. Degradation in Soil Degradation of pesticides in soil consists of nonbiological degradation, such as photolysis and hydrolysis, and biological degradation by soil microorganisms and other organisms. The involvement of microorganisms is especially great (Bollag et al., 1990; Turco and Konopka, 1990). A number of different microorganisms come into play until a certain chemical is com- pletely broken down, and sometimes nonbiological chemical reactions pro- ceed in parallel with biological decomposition. Various decomposing organisms have been separated out from soil; examples of decomposing microorganisms isolated from soil are bacteria, actinomycetes, molds, and yeasts (Goring et al., 1975). Decomposition by microorganisms proceeds dif- ferently according to the chemical structure of a pesticide and becomes more difficult as the sizes of molecules, and as their carbon numbers and numbers of rings, increase. Generally, water-soluble pesticides degrade easily, while 920103_CRC20_0904_CH13 1/13/01 11:10 AM Page 279 280 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT fat-soluble chemicals are adsorbed into soil, making it difficult for microor- ganisms to break them down. Decomposition reactions include thioether oxi- dation, epoxide and thioether formation, dealkylation, dehalogenation, reduction, formation of azo compounds, condensation, and isomerization; ultimately the chemicals are broken down to carbon dioxide (Scheunert, 1992; Kuwatsuka and Yamamoto, 1998). However, it is rare that microorgan- isms break carbon-chlorine bonds at a benzene ring, which is why represen- tative organochlorines such as DDT and BHC remain in the environment for long periods of time and, as a result, are highly bioconcentrated. Decomposition by microorganisms is greatly affected by the nature of the soil, and even in the same soil other major factors include temperature, mois- ture content, and the states of oxidation and reduction. There are very large differences in breakdown products and the degradation rate depending on whether soil is aerobic or anaerobic. For example, pesticides like DDT and BHC, which are decomposed mainly by anaerobic bacteria, degrade quickly in flooding soil (Lichtenstein and Schulz, 1961). Furthermore, the more organic matter contained in soil, the larger the number of microorganisms involved in degradation, which means that pesticide breakdown activity is greater. And because the decomposing bacteria types for each pesticide have their optimum pH values, soil pH also influences the degradation rate. When the same pesticide or chemicals with similar chemical structures are used continuously, the corresponding decomposing microorganisms accu- mulate, which sometimes leads to decreased sustainability of a chemical’s efficacy (Chapman and Harris, 1990). Especially pesticides having carbamate (N-CO-O), urea (N-CO-N), ester (COO-C), thiocarbamate (N-CO-S), and the like in their chemical structures undergo cross adaptation, in which degra- dation is promoted and chemical efficacy is considerably reduced (Roeth et al., 1990; Somasundaram and Coats, 1990). Measures to address this problem include the control of microorganisms’ decomposition activity by using extenders, and rotating the pesticides used (Drost et al., 1990; Harvey, 1990). PESTICIDES IN AQUATIC ENVIRONMENT Runoff from Farmland to Aquatic Environment Water is a chief vehicle for the movement of pesticides in the environ- ment. Additionally, because water in the environment is used as drinking water, and it plays a major role in the conservation of aquatic organisms, it is important to reduce to the greatest possible extent the risk of contaminating rivers and groundwater with pesticides. When pesticides are applied to upland fields, the chemicals that fall to the soil surface enter the aquatic environment, such as a river, lake, or sea, with rainwater that overflows from the soil surface if heavy rain falls from 920103_CRC20_0904_CH13 1/13/01 11:10 AM Page 280 ENVIRONMENTAL FATE OF PESTICIDES 281 the time directly after application to within about two weeks after (Wauchope, 1978; Leonard, 1988). In particular, the shorter the time elapsed since application, the greater the amount of pesticide runoff caused by rain- fall. With the passage of time, the amount of chemical runoff into aquatic environment lessens because the chemicals move downward from the soil surface and are more firmly adsorbed into soil particles and absorbed by crops, in addition to being broken down. The runoff rate into water systems is about 0.5% of the applied amount if rain falls immediately after applica- tion, and even a generous estimate puts the total runoff rate two weeks after application at 1 or 2% (Leonard, 1990). One factor governing runoff is the water solubility of pesticides, and, in general, the more water soluble a chem- ical is, the greater its runoff rate. Runoff into aquatic environment is also gov- erned strongly by environmental factors. Specifically, pesticides with water solubility of 10 ppm or higher mainly move to the aquatic environment by dissolving into surface water, while those that dissolve with difficulty or have high soil adsorption move with soil particles suspended in water or sed- iment to which the chemicals have been adsorbed (Turco and Kladivko, 1994). Thus, when surface water contains a large amount of minute soil par- ticles, pesticides tend to be washed off while adsorbed to those particles. Some characteristics of farmland on which surface water runoff easily occurs are slopes, hard soil with low water permeability, furrows running uphill/downhill, and exposed soil (Fujita, 1998). It is important to implement fully farmland soil erosion control and water management in order to curb pesticide runoff into the aquatic environment. Pesticide movement by means of soil moisture percolation into the ground brings about groundwater pollution. Especially when pesticides are highly water-soluble, when soil is sandy with little clay or organic matter, or when soil moisture has increased suddenly, pesticides are detected in groundwater (Cohen et al., 1990). In western countries, where groundwater is often used as drinking water, the detection of pesticides in the water of about 30% of wells in the 1980s became a matter of public concern. Some of the chemicals detected with especially great frequency were the soil fumigant ethylene dibromide (0.05–20 ppb), the carbamate insecticide aldicarb (1–50 ppb), and the triazine herbicide atrazine (0.3–3 ppm) (Cohen et al., 1986). Because of this situation, the U.S. Environmental Protection Agency (EPA) and agencies of other western countries established pesticide concentration standards for groundwater and continue strict monitoring of pesticide use (Kidd and Hartley, 1987; U.S. EPA, 1991). Factors involved in movement into the groundwater can be categorized as pesticide characteristics and as environmental conditions such as those of soil. Because farmland does not necessarily have homogeneous soil struc- tures, it is hard to discern uniform trends for each field owing to rainfall, soil conditions, and other factors. Below are some conditions that create a major potential for groundwater contamination: 920103_CRC20_0904_CH13 1/13/01 11:10 AM Page 281 282 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Pesticide characteristics: Water solubility of 30 mg/l or more; Koc value under 500; Henry’s constant under 10 Ϫ2 atm . m 3 /mol; neg- atively charged at ambient pH; half-life by hydrolysis of 25 weeks or more; half-life by photolysis of one week or more; and half-life in soil of three weeks or more. Farmland conditions: Annual rainfall of 25 cm or more; high possibil- ity of pesticide contamination in area with high nitric acid ion con- tent in groundwater; places with porous soil above aquifer; and soil that has pH providing for high stability of a certain pesticide. Pesticides applied on paddy field are dispersed into aquatic environment over broad areas while being diluted as they follow a path from agricultural water channels to small rivers and then to large rivers. The concentrations of pesticides in paddy surface water differ according to the amount applied per unit area, the manner of formulation, physicochemical characteristics, and environmental conditions, including temperature, rainfall, and soil charac- teristics. Generally the greater a pesticide’s water solubility, the higher the concentration. The highest concentration is found between the time immedi- ately after application and the following day, and many pesticides have short half-lives of two to five days in paddy surface water (Maru, 1985; Nagafuchi, 1999). Because most of the pesticide applied to paddy fields directly enters its surface water, the runoff rate from the fields into the aquatic environment is larger than that from upland fields. The runoff rate also varies according to application amount, water management, and other factors, but in particular one can discern a positive correlation between a pesticide’s runoff rate and its water solubility (Inao et al., 1999; Maru, 1990). For example, Maru calculated the pesticide runoff rate on the basis of regular pesticide concentration analy- sis results for paddy surface water and river water, and the pesticide appli- cation amounts for the surrounding region (Maru, 1991). Results showed that the water solubilities of the herbicides chlornitrofen, butachlor, thiobencarb, and simetrine were 0.25, 23, 30, and 450 ppm, while their runoff rates into river water were 0.11, 2.32, 1.44, and 5.96%, respectively. The higher the water solubility is, the higher the runoff rate, with the following regression equa- tion relating the runoff rate to the logarithmic value of water solubility: Y ϭ 1.06 ϩ 1.84 log (X), r ϭ 0.75 and n ϭ 10. where Y is runoff rate and X is water solubility. The period during which pesticides are detected in the aqueous environ- ment corresponds to their time of application. Often there is a temporary peak in the amount detected immediately following application, after which there is a gradual decline, with the chemicals becoming undetectable after two or three months. The concentration detected in river water is sometimes a high value of 100 ppb for a short time with the herbicide molinate, which 920103_CRC20_0904_CH13 1/13/01 11:10 AM Page 282 ENVIRONMENTAL FATE OF PESTICIDES 283 has a high water solubility of 900 ppm, but generally the concentration is in the range of 0.1 to 10 ppb (Nakamura, 1993). Degradation in Aqueous Environment Pesticides that have entered into water disappear by adsorption to soil particles, settling to sediment, atmospheric dispersion by evaporation with water, or a variety of breakdown reactions. Table 13.2 classifies the persistence of pesticides in water by their half-lives, which depend largely upon their chemical structures (McEwen and Stephenson, 1979). Half-lives range from those less than two weeks for organophosphates and carbamates to the long- term stability of over six months for chlorinated pesticides. Degradation of pesticides in water is accomplished by chemical reactions, mainly hydrolysis; physical reactions caused by photolysis; and biological reactions carried on by microorganisms. The prevailing breakdown reaction is determined by a pesti- cide’s chemical structure and conditions in the aqueous environment (Pollard et al., 1998; Kato, 1998). The author’s measurements of the breakdown rates in Table 13.2 Half-lives of Pesticides in Aqueous Environment (A) (B) (C) (D) Organophosphorous Organochlorines Organochlorines Organochlorines azinphosmethyl aldrin chlordane dieldrin chlorpyrifos methoxychlor lindane endrin, BHC demeton Organophosphorus Organophosphorus heptachlor dichlorvos diazinon chlorfenvinphos Benzimidazoles fenitrothion disulfoton dimethoate benomyl malathion phorate fensulfothion naled Carbamates Carbamates phosphamidon chloropropham aldicarb Carbamates EPTC, swep carbofuran carbaryl propham, Triazines methiocarb vernolate atrazine, simazine propoxur Benzoic acids propazine Pyrethroids chloramben Uracils pyrethrum Triazoles bromacil, terbacil Aryloxyalkanoic amitrol Dinitroanilines acids Ureas trifluralin 2,4-D fenuron, monuron Ureas Aryloxyalkanoic diuron, linuron acids MCPA Half-lives (A) Ͻ 2 weeks; (B) 2–6 weeks; (C) 6 weeks–6 months; (D) Ͼ 6 months 920103_CRC20_0904_CH13 1/13/01 11:10 AM Page 283 284 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT aqueous environments with different qualities showed that these environ- ments were ranked, from highest to lowest rates, in the order of river water, lake water, seawater, and groundwater. Thus, pesticides remained for a long time in groundwater (Hiramatsu, 1990). The main degradation factors under freshwater conditions of rivers and lakes are breakdown by microorganisms, and in seawater by weakly alkaline hydrolysis (Kanazawa, 1987). Sunlight-induced photolysis is an important degradation factor of pesti- cides in rice paddy water and the surface layer of river water, but at depths greater than this, where the energy of sunlight is reduced, the contribution of photolysis is reduced (Oyamada and Kuwatsuka, 1986; Yamaoka et al., 1988). As photochemical reactions occur in the wavelength region of 290–450 nm, the more ultraviolet light a pesticide absorbs, the more susceptible it is to photolysis (Crosby, 1969). Additionally, aqueous environments contain such photosensitizing substances like chlorophyll, carotenes, quinones, riboflavin, humic acid, and amino acids, which catalyze light reactions. Roughly, there are two photosensitizing reactions: (1) energy absorbed by photosensitizing substances is passed to coexisting substances (pesticides in this case) where it brings about chemical reactions; (2) oxygen is activated by the action of photosensitizing substances, thereby forming powerful oxidants such as hydroxyl radicals, peroxides, and superoxidoanions, which then promote oxidation reactions (Nakagawa, 1990). Microbial degradation in water generally proceeds readily under aerobic conditions, just as in soil, but in the water of a flooded paddy field and sedi- ment, degradation becomes quite anaerobic, and in some situations a few chlorinated organic pesticides readily undergo dechlorination reactions under anaerobic conditions (Marth, 1966; Johnson, 1976; Kanazawa, 1987). Under whatever conditions, microorganisms use enzymes to completely degrade pesticides to carbon dioxide by oxidation, reduction, hydrolysis, and other reactions. As a test for degradation in water by microorganisms, the Overseas Economic Cooperation Fund (OECD) and the EPA propose a method that involves adding microorganisms from river sediment or farm- land soil that has stable microbial flora. PESTICIDES IN THE ATMOSPHERE A comprehensive review of existing literature on the occurrence and dis- tribution of pesticides in the atmosphere showed that the atmosphere is an important part that acts to distribute and deposit pesticides in areas far removed from their application sites. A compilation of existing data is that pesticides have been detected in the atmosphere throughout the world, but most of the available information is from small-scale, short-term studies, few of which lasted more than one year. Until the 1960s atmospheric pollution from pesticide spray drift was generally thought of as a local problem. Long- range movement of long-lived pesticides through the atmosphere was 920103_CRC20_0904_CH13 1/13/01 11:10 AM Page 284 [...]... carcinogenicity and endocrine disruption The thinning of egg shells observed in pelicans, European sparrow hawks, grey herons, and other birds is suspected to be caused by the endocrine-disrupting effect of DDE, a metabolite of the highly persistent pesticide DDT (Mendelssohn, 1972; Brown, 1978) 920103_CRC20_0904_CH13 290 1 /13/ 01 11:10 AM Page 290 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT. .. weather conditions Wind Erosion Soil particles to which traces of pesticides adhere are swept up by strong wind near the ground and deposited on the field or neighboring region 920103_CRC20_0904_CH13 286 1 /13/ 01 11:10 AM Page 286 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Wind erosion of pesticides, mainly herbicides, is limited to treated fields of late sprouting crops such as root... Washington, D.C., 82–97 Chiou, C.T., Freed, V.H., Schmedding, D.W., and Kohnert, R.L., 1977 Partition coefficient and bioaccumulation of selected organic chemicals Environ Sci Technol., 11:475 –478 920103_CRC20_0904_CH13 292 1 /13/ 01 11:10 AM Page 292 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Cohen, S.Z., Eiden, C., and Corber, M.N., 1986 Monitoring ground water for pesticides, in. .. molecules become involved in the microphysical processes of cloud and mist formation that take place there, or they enter the rain directly when it washes them out of the air beneath the cloud Locally high concentrations of pesticides in rain and air are very seasonal and are correlated to local use The highest concentrations in air and rain usually occur in the spring and summer months, coinciding with application... In sensitized photodegradation–which affects mainly active ingredients that are absorbed onto the surfaces acting as a sensitizer (e.g., a 920103_CRC20_0904_CH13 288 1 /13/ 01 11:10 AM Page 288 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT formulation component)—the substance absorbs light and undergoes a transition into the triplet state Owing to the relatively long lifetime of the triplet... be put into categories including (1) direct effects on organisms in the vicinity, (2) secondary effects through food, (3) decreases in species that provide food and habitat, and (4) decreases in competing and predatory species In some situations pesticides affect the balance of species in an ecosystem; for example, the effects of a pesticide on natural enemies or other organisms might instead increase... parathion in a fish pond ecosystem and its impact on food-chain organisms, in Agrochemical Residue-Biota Interactions in Soil and Aquatic Ecosystems, International Atomic Energy Agency(IAEA) (Ed.), Vienna, 125–151 Gaynor, B and Mac Tavish, D C., 1981 Movement of granular simazine by wind erosion, Hort Science, 16:756 –757 Glotfelty, D.E., Meredith, M.M., Jersey, J., and Tayler, A.W., 1989 Volatilization and. .. times and warmer temperatures However, insecticide concentrations in air, rain, and fog can also be high during autumn and winter in some areas if there is high use at that time These off-season occurrences could be due to volatilization and wind erosion of previously applied pesticides, or the result of longrange transport from areas where the growing season started earlier Degradation of Pesticides in. .. and maize, with long vegetation-free periods in autumn and spring Herbicides are applied mainly during the early developmental stage of crops, i.e., when soil cover is still modest Most of the applied mixture reaches the soil; only a minor portion wets the growing weeds and the crop directly Depending on its physicochemical properties, a fraction of the applied active ingredient may remain longer in. .. 1976 Estimation of environmental partitioning of organic chemicals in model ecosystems Residue Rev., 85:231–244 920103_CRC20_0904_CH13 294 1 /13/ 01 11:10 AM Page 294 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT McCall, P.J., Swann, R.L., Laskowski, D.A., Unger, S.M., Vrona, S.A., and Dishburger, H.J., 1980 Estimation of chemical mobility in soil from liquid chromatographic retention . . . 291 275 0-8 49 3-0 90 4-2 /01/$0.00+$.50 © 2001 by CRC Press LLC 920103_CRC20_0904_CH13 1 /13/ 01 11:10 AM Page 275 276 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT INTRODUCTION Pesticides. time. 920103_CRC20_0904_CH13 1 /13/ 01 11:10 AM Page 277 278 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Table 13. 1 Half-lives of Pesticides in Upland Soil (A) (B) (C) (D) alloxydim(H). pesticides having carbamate (N-CO-O), urea (N-CO-N), ester (COO-C), thiocarbamate (N-CO-S), and the like in their chemical structures undergo cross adaptation, in which degra- dation is promoted and chemical