Research is needed to elucidate the processes of agrochemical function in order to maximize efficacy, determine more realistic exposure potentials to biota (including humans) from foliar, soil, water and airborne agrochemical residues, and develop exposure minimization strategies. Investigations are required to better understand the mechanisms of agrochemical loss processes and the influencing cultivation practices and environmental and matrix variables, such as temporal and diurnal terms, soil composition, moisture levels, sorption, organic carbon, solutes and abiotic and biotic transformation mechanisms. Low level chronic exposure effects will be determined, more appropriate biomarkers evaluated, and analytical methods with lower detection limits developed.

Analytical Techniques. Supercritical (i.e., SC-CO₂) and pressurized fluids can be used for extraction of non-polar or slightly polar compounds from complex media with considerable extraction selectivity and minimum solvent disposal, but are less effective in recovering polar molecules because of the properties of SC-CO2 and pressurized fluids (Chester et al., 1998; Westwood, 1993). Many polar solvents have been added in SC-CO2 to alter its polarity and subsequently to improve extraction efficiency of some polar herbicides from solid matrices (Reighard and Olesik, 1998). Derivatization of polar analytes or sorption sites in situ or off-line have received considerable attention (Hawthorne et al., 1992). Quantitative recoveries have been achieved for thirty polar chemicals in soils using SC-CO2 with assistance of (ethylenedinitrilo) tetraacetic acid tetrasodium salt (Na4EDTA) (Alcantara-Licudine et al., 1997; Guo et al., 1999). The procedure can also be used to recover neutral and nonpolar compounds from soils and has potential for the analysis of parent analytes and polar biomarkers simultaneously.

Immunoassays are recognized as valuable alternatives to the conventional methods for monitoring agrochemical residues because they have a low detection limit, are highly specific, provide fast analysis, and are inexpensive, e.g., immunoassay analysis is $20-40 per sample compared to $150-500 per analysis for instrumental methods such as gas chromatography. (Aga and Thurman, 1997). Immunoassays and immunosensors have been developed for a number of pollutants including polycyclic aromatic hydrocarbons (PAHs) (Li et al., 1999; Liu et al., 1999a, b). Development of these methods will be invaluable for fast and large throughput monitoring of environmental samples.

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Weed Management. To predict and manage rangeland weed populations and to minimize negative impacts on surrounding biota characterization of crops, weeds, and herbicide interactions is needed. Broom snakeweed is a weed threatening livestock productivity. Research concerning the fate, action, and resistance of the rangeland herbicide, picloram, indicated that the extent and rate of adsorption by broom snakeweed foliar tissue was influenced by relative humidity, air temperature, solution pH, and additives (Sterling and Lownds 1992). However, herbicide differential sensitivity may be more strongly related to differences in picloram translocation or metabolism. Studies showed that picloram translocation did not parallel carbohydrate redistribution, thus, herbicide application in the fall, as is commonly hypothesized due to more herbicide being transported to the roots during the rainy season, may not improve efficacy. Furthermore, variable metabolism as a function of snakeweed species and stage of growth may be responsible for differences in whole plant sensitivity throughout the year (Hou and Sterling 1993). In other studies, the mechanism of picloram resistance in yellow starthistle may involve the auxin receptor sites in herbicide perception and signal transduction (Sabba et al., 1998; Sterling et al., 1998). Resistance was determined to not be a function of differences in foliar absorption, translocation, or metabolism (Fuerst et al., 1996).

Oxidative stress is the major factor limiting plant productivity and results from environmental stresses which induce the production of active oxygen species capable of severe cell and tissue damage. Cotton tolerance variablity to the major herbicide prometryn, a photosynthetic inhibitor, is not due to differences in uptake, translocation, or metabolism or to differences at the site of action. Evidence suggests that the protective mechanisms against photo-oxidative stress, due to blocked photosynthetic electron transport caused by these herbicides, contribute to tolerance (Waldrop et al. 1996). This research will provide a basis for understanding the variation in biochemical and physiological strategies in cotton protecting it from herbicide photoinhibition. By understanding how plants avoid oxidative stress, crops will be better protected from stress and weeds better managed.

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Agrochemical Fate as Affected by Transport and Partitioning. Offsite movement, locally and globally, of agrochemicals can be a potential source of air, water, and soil pollution. Agrochemicals applied during the spring in the Chesapeake Bay watershed have been be measured in air and water throughout the year (Glotfelty et al. 1990; McConnell et al 1997). Regional agrochemical airborne transport from California's central valley and deposition to the Sierra Nevada Mountains has been reported (Zabik and Sieber, 1993; McConnell et al., 1998). More persistent agrochemicals, such as the organochlorine insecticides, have been found in the polar regions, areas quite remote from their application sites (Muir et al., 1990; Bidleman et al., 1990, Rice et al, 1998). Renewed interest exists in flux measurement research (Majewski et al. 1995), and the need to attempt mass balance determinations and to use multiple methods for flux estimations (Yates et al., 1996).

During application, the active ingredient may move offsite as fine droplets (spray drift) particulates, or as vapor. The environmental fate of these forms can be distinct. Spray drift has been examined (Haq et al., 1983; Miller, 1993; Ware et al., 1970; Ware, et al. 1972) as well as the effect of temperature and humidity on droplet size (Freiberg and Crosby, 1986; Sundaram, 1985). However, comparatively little work has focused on the volatilization of active ingredient directly from spray droplets. For agrochemicals with low volatility, direct evaporation of active ingredient from spray droplets is expected to play a minor role compared to droplet drift but maybe significant on a regional scale. When the chemical remains within a droplet, the droplet may eventually leave the atmosphere by impacting a surface. Little information is available on the factors influencing these mechanisms or how they might be altered to improve on-target deposition.

Distribution of agrochemicals by volatilization is largely controlled by the physical and chemical properties of the agrochemicals. These include vapor pressure and solubility (Henry's Law constant), organic carbon partition coefficients, and degradation rates (Jury et al.,1984a, 1984b, 1984c; Robbins 1993; Staudinger and Roberts 1996). Determination of Henry's law constants over a temperature range have been conducted (Sagebiel et al., 1992) although few studies actually examine the effect of aqueous parameters on the air/water partition coefficients (Rice et al. 1997, Staudinger and Roberts 1996) which can influence fate and transport predictions.

Soil fumigants are relatively toxic to a broad spectrum of organisms and their high vapor pressures result in significant atmospheric loss. Research has focused on determining rates of volatilization and degradation under various conditions and the use of impermeable tarps following fumigation to reduce volatile losses. Preliminary results indicate that fumigant application rates can be reduced when using virtually impermeable films (VIFs) because the fumigant is held in the soil at higher concentrations for a longer period (Gan et al., 1996). Additional research is needed to develop management practices using VIFs to ensure low emissions and sufficient pest control.

Agrochemical sorption to, and interactions with organic carbon, clays and minerals can alter the structure, reactivity, bioavailability, solubility, partitioning, and, ultimately, transport (Brusseau et al., 1991a, 1991b; Brusseau and Rao 1991; Gamerdinger et al., 1991; Hassett et al., 1985; van Genuchten and Waganet 1989; Wu and Gschwend 1986). In addition, the elution of freshly added agrochemicals from soil has been reported to be far greater than in “aged” samples (Pignatello et al., 1993). Current research result cannot adequately predict sorption.

Runoff and erosion from agriculture have been identified as major contributors to water quality degradation. The U.S. EPA estimates routine agricultural activities are responsible for more than 60% of the nation’s surface water pollution problems (USEPA 1998). Approximately 1 to 6% of applied agrochemicals may be transported off-site by runoff and drainage depending on the slope of the field, management practices, presence or absence of subsurface drains, and the quantity and timing of rainfall after application (Bengtson et al., 1990; Leonard, 1990).

Plastic mulch vegetable production systems use extensive amounts of agrochemicals and also have a greater potential for off-site movement of agrochemicals during rain events due to the use of an impervious surface. During an intense rain event, a large pulse of runoff water can quickly move into surrounding surface waters where agrochemicals in the runoff can cause potentially acute toxic effects on aquatic organisms (Rice et al, 1999). Other studies have demonstrated significant negative effects of agrochemicals on aquatic plants (Forney and Davis, 1981; Jones and Winchell, 1984) and other organisms (Clark et al., 1993; Savitz et al., 1994; Scott et al., 1990; Scott et al., 1992). Research is needed to develop technologies to mitigate these negative impacts.

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Transformation Processes - Photolysis. Environmental photolysis can proceed either by direct photolysis or indirect photolysis where another matrix component absorbs the solar light energy and then interacts with agrochemicals, causing decomposition via energy transfer (sensitization), direct electron transfer or other free radical processes (Zafiriou et al., 1984; Draper and Wolfe 1987; Miller and Hebert 1987). Photolytic degradation can occur in the atmosphere, in aqueous systems, within the first millimeter of soil, or on foliar surfaces.

DOM (dissolved organic material), NO3 anion, and other compounds can serve as sensitizers (Zepp et al., 1981, 1987) or precursors for the production of singlet O2 (Faust and Hoigne, 1987; Haag and Hoigne 1986; Zepp et al., 1977), peroxy radicals (Faust and Allen 1992), H2O2 (Draper and Wolfe 1983), e- and OH radical (Draper and Wolfe 1981; Haag and Hoigne 1985; Faust and Allen 1993). Alternatively DOM can alter the rate of agrochemical degradation by absorbing the available light energy (Hapeman et al., 1998; Hoigne et al., 1989; Kochany and Maguire 1993; Torrents et al, 1997). Understanding the competing mechanisms is required to accurately assess the fate of agrochemicals in systems that are subjected to solar irradiation.

While atmospheric chemistry is a relatively mature science for small molecules, the atmospheric fate of medium weight organic chemicals, particularly agrochemicals, is not well understood as maintaining stable agrochemical concentrations in the gas phase is difficult. Chemicals with vapor pressures less than 10^-3 torr sorb on the walls of chambers and the observed chemistry is complicated by reactions on the walls. Thus, risk assessments of many agrochemicals rely on incompletely tested computer models for reactions. Both the short and long range transport of agrochemicals has been firmly established and currently represents a significant risk to humans and the environment (Majewski and Capel, 1995)

Methods to assess the gas phase reactions of volatile compounds with hydroxyl radical are available (Atkinson, 1986) which utilize several compounds as stable tracers with known hydroxyl radical reactivity. Nevada scientists are continuing to develop methods for applying these methods to agrochemicals using special temperature controlled chambers and solid phase microextraction devices to reliably establish and measure pesticide gas phase concentrations (Hebert, et al., 1999a, 1999b). These methods need to be applied to many of the major agrochemicals for which risk assessments are complicated due to the paucity of data concerning their atmospheric dagradation.

Initial studies have shown that herbicide photodegradation rate on leaf surfaces is influenced by epicuticular wax and the plant species. Additional photodegradation products on wax surfaces were detected relative to photodegradation on glass surfaces only (Maynard and Sterling 1996). Thus, herbicide not absorbed by the plant is subject to photodegradation, reducing plant exposure to the toxic parent herbicide and limiting product efficacy.

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Other Abiotic Processes. Agrochemicals that are susceptible to environmental hydrolysis generally include esters, carbamates, organophosphates, and activated amides. Hydrolysis typically occurs in the presence of an acid, base or heterogenous catalyst usually in aqueous environments in the atmosphere or soil or at the catalytic surface. Dechlorination of the chloro-s-triazines can also be described as a hydrolytic reaction, typically occurring under acidic conditions or in the presence of an acid catalyst (Gamble and Khan 1985, 1990; Gamble et al., 1983). This process was also thought to be a hydroxy radical process but recent studies have shown that direct photolysis is more likely to be responsible for hydroxyatrazine formation (Torrents et al., 1997). Understanding the preferred degradation pathway and the environmental factors that influence transformation is required to make reasonable risk evaluations.

Enhanced abiotic and biotic degradation of soil fumigants has also been observed in soils to which organic amendments have been applied. Many soil fumigants, which contain halogenated alkyl groups, can undergo abiotic degradation via nucleophilic reaction. This reaction mechanism likely occurs in unamended soil (with nucleophilic groups on soil organic matter acting as the nucleophile) and is accelerated in soil treated with nucleophilic compounds. Thiosulfate compounds, such as ammonium thiosulfate, an S fertilizer, were found to be capable of rapidly transforming several fumigants into water soluble products (Gan et al, 1998) and reduce fumigant atmospheric emissions. Optimization of this management technique demands elucidation of mechanisms and control factors.

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Microbial/Enzymatic Processes. Microorganisms clearly play a vital role in the degradation and transformation of agrochemicals in soils and water (Alexander, 1999). Enhanced degradation of soil fumigant compounds observed in soils receiving repeated applications has been attributed to an increase in the rate of biological degradation although the mechanisms underlying enhanced degradation remain largely remains unexplored (Alexander, 1999; Ou, 1999). Extensive information on degradation rates of agrochemicals in root-zone soils has been generated, but much less in vadose-zone soils. .

Indigenous soil and water-borne bacteria can degrade agrochemicals and may prevent carry over to next growing season, leaching into the groundwater, and volatilization into the atmosphere. Ammonia and methane oxidation bacteria has been utilized to degrade the fumigants in soil (Ou et al., 1997; Oremland et al., 1994). A strain of Arthrobacter sp. capable of extensively degrading 1,3-D, a possible alternative to methyl bromide, has been isloated from an enhanced soil. This organism can be used potentially to degrade 1,3-D from soil after fumigation is completed. This rapid degradation of the chemical will minimize volatilization into the atmosphere and percolation into the groundwater.

For some agrochemicals, toxic metabolites, which have similar activity and toxicity as their parent chemicals, may accumulate in soils. For example, aldicarb sulfoxide and aldicarb sulfone, and fenamiphos sulfoxide and fenamiphos sulfone are formed in soils treated with aldicarb (Ou et al., 1985) and fenamiphos (Ou et al., 1994), respectively. Thus, it is more accurate to include these toxic metabolites for estimation of degradation rates as total toxic residue disappearance rates (parent chemical + toxic metabolites).

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Agrochemical Toxicity - Organophophates (OP), Carbamates, and FQPA. OP and carbamate insecticides are designed to inhibit acetylcholinesterase (AChE), the enzyme that normally hydrolyses the neurotransmitter acetylcholine in nerve and muscle tissues. In the presence of an OP, synaptic acetylcholine levels may rise to abnormally high levels resulting in repetitive stimulation of muscarinic and nicotinic receptors in target tissues. At sufficiently high exposure levels, this produces clinical signs of acute cholinergic poisoning. Recovery is possible if the individual is removed from further exposure, allowing OP clearance from the body and a return to normal levels of synaptic acetylcholine. Long-lasting neurological damage from acute high level exposure to some OPs is well documented (Karczmar, 1984).

OP and carbamate insecticide fate in orchards has been primarily concerned with worker reentry hazard associated with foliar dislodgeable residues, soil, and soil dust residues because of their acute mammalian toxicity. Most of this work has been done for citrus (Spear et al., 1975; Thompson and Brooks, 1976; Gunther et al., 1973, 1977; Nigg et al., 1977; Iwata et al., 1982, 1983; Nigg et al., 1984), but studies have also been conducted on peach (Winterlin et al., 1975; Hansen et al., 1978; Spencer, et al, 1991, 1993, 1995) and apple orchards (Staiff et al., 1975; Hansen et al., 1978). Dislodgeable residues and worker exposure in strawberries has been studied (Winterlin et al., 1984; Zwieg et al., 1983, 1984; Popendorf et al., 1982). Few studies report monitoring of both dislodgeable and airborne residues (Winterlin et al., 1986, Jenkins et al., 1990). Another emerging area of interest is the potential for exposure to agrochemicals from turf (Goh et al., 1986, Sears et al., 1987, Cooper et al., 1990; Jenkins et al., 1990, 1991).

From these studies and others, protective clothing requirements and reentry intervals have been established for farm workers. Despite these precautions, a heightened awareness exists for the health hazards to any person who might be exposed before, during, or after agrochemical application. This concern is due, in part, to current risk assessment guidelines under the (FQPA) that require cumulative risk from all sources of exposure (dermal, inhalation, dietary, drinking water) be considered. For those agrochemicals with a common mode of action, such as the OPs and carbamates, aggregate risk must also be considered. Also, the increased use of Integrated Pest Management (IPM), which often requires frequent human (consultants, scouts, etc.) exposure to the orchard environment, has increased the number of individuals who are potentially at risk. It is these individuals, as well as the general public, who are at the greatest risk as they are often unaware of the hazard of inhalation or dermal contact with pesticide residues and do not take the appropriate precautions.

To determine exposure to specific classes of organophosphate and carbamate chemicals, California and other states require or recommend blood cholinesterase monitoring for mixer-loaders, applicators and farm workers. Methods have progressed from manometric determinations through pH assays to thiocholine ester (Ellman et al, 1961, Metcalf R.L, 1951 ; Wills, 1972). Blood cholinesterase activity does not appear to be involved in neurotransmission (the function of cholinesterases present in the blood is not known), but inhibition of these enzymes is used as a biomarker of exposure to OPs. Although a number of field studies of blood cholinesterase levels exist, the test accuracy has not been scrutinized until recently. Major inadequacies in two major commercial kits used by clinical testing laboratories have been indicated, one uses a pH and a substrate concentration that is 40% from optimum and the other uses an inappropriate substrate (Wilson et al, 1997). This has prompted a change in state regulations requiring optimum assay conditions.

OP exposure can also be monitored by the presence of dialkylphosphate metabolites in urine (Drevenkar et al., 1991; McCurdy et al., 1994). While this method can detect low level exposure, the rapid elimination of urinary dialkylphosphate metabolites makes them useful for assessing only recent exposures (less than 48 hours) (McCurdy et al., 1994). Biological samples often become available only days or even weeks after exposure. Analogous procedures were recently utilized in persons who treated their residences with insecticides in the IPM of fleas. These studies with chlorpyrifos as a model compound have shown that normal exposures are low (less than 6 ug/kg) but more prolonged than predicted by available hypothetical exposure models. Clearance is maximal during the first week and declines during the subsequent weeks to levels that are at or similar to background. No adverse effects have been reported during these studies, but the availability of the indoor residue has been substantially clarified (Kreiger unpublished results).

Possible consequences of chronic low-level exposures to OPs are not well characterized. Several studies have found significant behavioral changes in animals dosed with OPs at dosage levels that produced little or no cholinesterase inhibition (Hart, 1993; Kurtz, 1977; Roney et al., 1986;Dutta et al., 1993;). OPs are often applied two or three times over several months, and workers may enter treated areas more than once after these applications presenting repetitive worker exposure risks. Available OP exposure monitoring methods have limited use for detecting chronic, low-level exposure. Wide individual variation in blood cholinesterase activity requires pre-exposure testing and limits its use as a quantitative biomarker of internal dose expecially at low exposure levels (Sanz et al., 1991).

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Other Agrochemicals. Some agrochemicals used currently and in the past are known to induce oxidative stress as part of their mechanism of action. Cadmium, cyanide, and mercury containing agrochemicals, for example, have been shown to induce oxidative stress (Vincent et al., 1989, Manca et al., 1991 Younes and Strubelt, 1988, Pritsos, 1997; Stacey and Kappus, 1982, Hoffman and Heinz, 1998). Cadmium has also been identified as a lung carcinogen in humans (IARC, 1993) and may be associated with hormonally mediated cancers by interactioning with steroid receptors (Antila et al., 1996; Garcia-Morales et al., 1994). Arsenic and cyanide based agrochemicals have been shown to interfere with normal mitochondrial function, inducing oxidative stress (Maupoil and Rochette, 1988, Kehrer et al., 1990). Lead-arsenal agrochemicals can affect cognitive development in children and renal function in adults (Goyer, 1989; Goyer, 1990). While many of these compounds have been studied in terms of their acute lethal toxicities, little work has been conducted to determine the biological effects of either acute or sub-chronic ingestion of non-lethal dosages.

Acute biological effects of mitochondrial damaging and oxidative stress inducing agrochemicals on target and non-target organisms have been examined. Studies were conducted using potassium cyanide and sodium arsenate as model agrochemicals, rats for examining effects on a targeted organisms, and mallard ducks as a model wildlife, non-targeted organism. Mitochondrial dysfunction with subsequent tissue energy (ATP) depletion due to cyanide exposure was shown in various tissues of both rats and mallard ducks (Pritsos, 1996; Pritsos and Ma, 1997). The mallard duck was much more sensitive to cyanide than the target organism (rat). ATP levels in the mallard duck were restored to normal within 24 h of exposure and that rhodanese and 3 mercaptopyruvate sulfur-transferase were induced (Ma and Pritsos, 1997). In other studies, increased flight times of homing pigeons were observed with exposure to increasing cyanide concentrations apparently due to loss of ATP (Ross and Pritsos, unpublished work).

Widely used herbicides, including the triazine herbicides atrazine, simazine and cyanazine, have been put under Special Review by EPA because experimental animal studies have shown they can cause mammary carcinogens and therefore may pose a potential cancer risk in exposed populations such as farm workers (Stevens et al., 1994; USEPA, 1994). Evidence also exists that the parent compound and degradation by products persist in the soil and low residue levels have been detected in ground and surface water in high use states (Kolpin et al., 1997; Koplin et al., 1998; Solomon et al., 1996; Thurman et al., 1998; Wall et al., 1998).

Critical evaluations, comprehensive reviews and in depth evaluations of the existing published and unpublished scientific literature on relationships between specific agrochemicals and the risk of breast cancer and other cancers have been developed in concert with USDA/CSREES grant #97-34369-4005. Copies have been made available to scientists at academic institutions and federal agencies. Previously prepared technical reports on triazine herbicides (atrazine, simazine, and cyanazine) have had widespread use by prominent scientists and policy makers including the Carcinogenicity Peer Review Committee at EPA, Agency for Toxic Disease Substances Registry, and the National Institute of Environmental Health Sciences. Translation of these critical evaluations into multiple formats for the non-scientist (fact sheets and tip sheets) in both print and electronic formats (http://www.cfe.cornell.edu/bcerf/) ensures distribution to diverse audiences, including the general consumer, underserved rural populations, health and extension educators, cancer survivors, advocacy groups, grant administrators, policy makers and media representatives.

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Discerning Biomarkers for Determining Exposure. Some agrochemicals have been implicated as endocrine disruptors affecting the reproduction of animals including the human. For example, methoxychlor, widely used for pest control in tomato production and a component of rose dust, has been identified as an environmental estrogen mimic adversely affecting experimental animal reproductive function (Cummings, 1997; Cummings and Perreault, 1999; Danzo et al., 1997). Fecal steroids biomarkers have been used to study the reproductive state in apes, mammals, birds and even prehistoric humans and typically involve radioimmune assays (Wilson and LeBlanc, 1998; Tell, 1997; Whitten, 1995 ; Cockrem and Rounce, 1994, 1995). Recently, male and female steroids ELISA antibody assays have been developed using animal feces (Tell, 1997; Cockrem and Rounce, 1995). Such non-invasive assays are especially important when dealing with animal welfare issues and when studying wildlife, particularly endangered species (e.g., Velloso et al, 1998). An antibody to testosterone and a method to study it in feces of rodents have been developed (Billitti et al, 1998).

Studies of the effects of OPs and other agrochemicals on the nervous systems and reproduction of domestic and experimental animals, wildlife and humans are in progress. The results suggest the techniques will provide useful biomarkers for studying the effects of chemical and environmental stresses. A combination of cadmium and an organophosphate was more toxic to nerve cell cultures than either chemical alone (Coatnery and Wilson, 1996). Additional studies are required to determine the combined effects on the developing nervous system of birds.

Hemoglobin adducts specific for OP exposure would be useful biomarkers for monitoring OP exposed individuals because of sampling ease, dose-dependent covalent binding, and long biological lifetime (120 days in humans) (Schell, 1994). Because red blood cells have a long biological lifetime, hemoglobin contained within them can integrate an individual's cumulative exposure over that time and retrospective exposure monitoring is possible. Hemoglobin adducts have been identified for a number of agrochemicals or their metabolites including dichlorvos, pentachlorophenol, linuron, and ethylenebisdithiocarbamates (Waidyanatha et al., 1996; Sabbioni and Neumann, 1990; Pastorelli et al., 1995; Segerback and Ehrenberg, 1981). More recently, initial studies using azinphos-methyl [14C] administered by gavage to rats showed a dose-dependent and stable association of radioactivity with red blood cells and hemoglobin (Bailey and Jenkins, 1999). Future research is needed to identify the adduct and adduction site and to develop analytical methods for trace level detection.

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Remediation Technologies. Research is needed to provide effective and inexpensive remediation technologies for agrochemically contaminated soils and water. Oxidative and reductive radicals produced by the enzyme or fungi may be useful for the biodegradation of older agrochemicals in soils. When wood-rotting fungi, such as Phanerochaete chrysosporium are grown on a substrate containing cellulose, such as wood, they produce an enzyme that can generate very reactive radicals. This may provide a mechanism to degrade a variety of chemicals, including agrochemicals. Mineralization of lindane, DDT and PCP occurred when the fungus was grown on cellulose. Furthermore, when oxalate, a secondary metabolite of P. chrysosporium, was used as an iron chelator for the purified enzyme, it was oxidized to produce a radical which reduced bromotrichloromethane to the trichloromethyl radical. (Aust 1997). Additional mechanistic research is required so that optimal mineralization conditions can be elucidated.

Constructed wetlands for agricultural runoff treatment is a relatively inexpensive alternative as compared to traditional treatment methods where the natural biodegradation processes can be optimized and exploited (Kirshner 1995). Wetlands are currently used to treat phosphorus, nitrogen, BOD, hydrocarbons, animal waste, and heavy metals from the municipal/animal, storm water, and mine wastes. Little evaluation of constructed wetlands to treat agrochemical runoff exists. This may be a function of the difficulty in analyzing complex agrochemicals and their transformation products, whereas metals, BOD, and nutrient are much easier to measure (Watanabe 1997; Thurman and Meyer 1996).

A synergistic relationship exists between chemical and biological methodologies in waste treatment (Hapeman-Somich, 1992). Biodegradation can be enhanced by chemical pretreatment, particularly oxidative approaches that involve the hydroxyl radical (Qian et al., 1985; Miller et al., 1988; Leeson 1993; Acher 1994 and Hapeman et al., 1995). The reaction should result in effluent detoxification and nearly complete mineralization, the method should be convenient and able to be used in situ (in field situations), and useful reagents should be recoverable whenever possible.

The effectiveness of the classic Fenton reaction and of an electrochemical Fenton reaction on the degradation have been evaluated (Dowling, 1992; Dowling and Lemley, 1995; Roe, 1996; Roe and Lemley, 1997; Pratap, 1992; Pratap and Lemley, 1994). The results provide base data for Fenton degradation of agrochemicals in distilled water using ferrous salt or by generating ferrous ion electrochemically. Further work has greatly improved the efficiency of the Fenton electrochemical system such that it works more effectively than the classic Fenton system (Pratap, 1996). Optimization of the hydrogen peroxide to ferrous iron concentration ratio and maintenance of a constant molar have resulted in this faster degradation (Pratap and Lemley, 1998). These new advances with an anodic Fenton treatment promise to provide a very effective approach to the Fenton remediation of pesticide wastes.

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