Pesticide conjugates

ELISA could potentially be used advantageously in many types of exposure and monitoring situations, for paraquat and other pesticides amenable to ELISA analysis. An obvious use of ELISA is the detection of pesticide residue levels in plant and animal tissues, or food extracts. Biological specimens such as plasma and urine currently analyzed by RIA seem particularly amenable to analysis by ELISA. Portable field kits could be developed to determine safe worker re-entry times into treated fields. Environmental samples such as soil, water, and air, can be analyzed by the ELISA. Pesticide conjugates have been proposed for skin testing of individuals suspected of sensitivity to pesticides (fi.) the ELISA could be used to detect specific antibodies in these individuals and aid in exposure studies. 

Dorough, H.W., Toxicological significance of pesticide conjugates, J. Toxicol. Clin. Toxicol.,... 

Pesticide Conjugates. Although the primary metabolism of pesticides does not necessarily result in a diminution of acute toxicity, secondary or conjugative reactions almost always do. Pesticide conjugates are usually highly polar (e.g., glucosides. 

Among the topics discussed were advantages of various detectors, packing techniques for columns, specificity of analyses, interpretation of spectra, advantages of buying a complete unit such as GC-MS coupled to a data system, cleanup techniques, and methods for cleaving pesticide conjugates. 

General Techniques. Cleanup of analytical samples can be done conveniently with Waters Sep-Paks or equivalents available from Extrelut or Merck, and they can be regenerated. The major problem in isolation, characterization, and analysis of pesticide conjugates is ensuring 1005 cleavage of many conjugates. 

Lange BM, N Hertkorn, H Sandermann (1998) Chloroaniline/lignin conjugates as model system for nonex-tractable pesticide residues in crop plants. Environ Sci Technol 32 2113-2118. 

The above examples can be extended to the majority of older and newer active substances described in, e.g., The Pesticide Manual and to numerous relevant metabolites featuring hydroxyl or carboxyl moieties or even for conjugates however, there remain various active substances and metabolites that still require careful and extensive method development. 

Miyake et al reported an ELISA method for the determination of pesticide residues in the aquatic environment. The polyclonal antibody and three monoclonal antibodies of acifluorfen were prepared by immunization of rabbits and mice with acifluorfen-bovine serum albumin conjugates. The polyclonal antibody reacted with acifluorfen at concentrations of 1.5-800 mg L , while the monoclonal antibodies reacted with acifluorfen at concentrations of 1.5-144 mg L . Among three monoclonal antibodies, AF 75-144 reacted with chlornitrofen, which did not react with the other two antibodies. It seems that the ELISA method is effective for the determination of herbicide residues in the aquatic environment. 

Stevenson F.J. Organic matter reactions involving pesticides in soil. In Bound and Conjugated Pesticide Residues, D.D. Kaufman, G.G. Still, G.D. Paulson, S.K. Bandal, eds. Washington American Chemical Society, 1976. 

Anti-12-hydroxyendrin and 12-ketoendrin were detected in the feces of pesticide manufacturing workers and its glucuronide conjugate and 12-ketoendrin have been detected in the urine (Baldwin and Hutson 1980). In another study, the levels of anti-12-hydroxyendrin increased accompanied by a sharp rise in D-glucaric acid levels in 29 workers after 7 days of exposure (Ottevanger and Van Sittert 1979 Vrij-Standhardt et al. 1979). 

The above classification of detoxication reactions has been developed for the metabolism of synthetic pesticides In plants. However, the same reactions can occur with natural exocons, such as allelopathic compounds, that have the same functional groups as synthetic pesticides. Most allelopathic chemicals contain functional groups that can be conjugated by Phase II reactions. Thus, detoxication of allelopathic compounds can be expected to proceed by conjugation with the omission of Phase I reactions. The remainder of this review will be concerned with the conjugation of allelopathic compounds. 

Dorough, H.W. In "Bound and Conjugated Pesticide Residues" Kaufman, D.D. Still, G.G. Paulson, G.D., Eds. ACS SYMPOSIUM SERIES No. 29, American Chemical Society Washington, D.C.,... 

Figure 4. Role of glutathione conjugation in dithietane pesticides...

Catabolism of Glutathione Conjugates of Pesticides in Higher Plants... 

In spite of the Importance of the Initial GSH conjugtlon reaction, very little Information Is present In the literature regarding the catabolism of GSH conjugates of pesticides In higher plants. The catabolism of the GSH conjugate of atrazlne In sorghum has been studied (Figure 1), but there appear to be few similar reports. 

Because of the Importance of GSH conjugation In pesticide metabolism and the diversity of the plant kingdom. It seemed desirable to study the catabolism of another GSH conjugate In several plant species. Pentachloronltrobenzene-UL- C,... 

Insoluble residues have been reported as important end-products in the metabolism of other pesticides known to be metabolized by GSH conjugation in higher plants (, 6, 2ii 15). Some insight into the mechanisms of insoluble residue formation was obtained by comparing the metabolism of [ ClPCNB, S-[() C)PCP]Cys and pentachlorothiophenol-UL- C (t" C]PCTP) in peanut root and peanut cell culture (Figure 12). 

These studies provided strong evidence that N-malonylcysteine conjugates may be produced from a variety of pesticide GSH conjugates in a variety of important plant species. These conjugates appeared to be stable end-products of metabolism. 

Evidence was also provided that Insoluble residues may be produced from GSH conjugates via cysteine conjugate or thiol Intermediates. These studies also suggested that certain reactions should be studied in greater detail to assess their importance in pesticide metabolism l.e., the C-S lyase reaction, the methyl transferase reaction, and the transamination reaction. 

The methods used for the isolation and derlvatization of the metabolites as well as the results from the detailed mass spectral studies presented in the original manuscripts (, 7) should have broad application in studies dealing with GSH conjugates of pesticides in plants. 

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