Department of Public Health Sciences

Cholinesterases and Agriculture: Humans, Laboratory Animals, Wildlife

Wilson, B.W., S.A. McCurdy, J.D. Henderson, S.A. McCarthy and J.E. Billitti

IN: Structure and Functions of Cholinesterases and Related Proteins. Doctor BP, Quinn DM and Taylor P ED. 539-546. Plenum Publishers. New York. 1999.

The widespread use of organophosphate (OPs) and carbamate esters (CAs) in agriculture and their stockpiling as chemical warfare agents has stimulated research into the detection of their residues and recognition of their effects. One popular biomarker has been cholinesterase (ChE) activity of blood and other tissues of humans, research animals and wildlife as a means to assess exposures, effect and risks of these powerful agents. This report briefly reviews work from our laboratory and colleagues that demonstrate the importance of blood ChE measurements for understanding the impact of pesticides on agriculture and society. Examples presented include: monitoring blood ChE levels of mixer loaders, applicators, farm workers and their families; setting safe levels of pesticides in foods; assessing the risk of agricultural chemicals to wildlife and to humans outside the agricultural workplace. Problems in measuring ChEs include: the lack of standardized clinical assays for humans and other animals; widespread reliance on commercial kits used without validating their assays for the situations at hand; improper collection and storage of samples; lack of understanding of the kinetics of the enzyme assays themselves. The consequences are widespread variability and inaccuracies of measurements. Such matters inevitably raise questions about the practice and quality control of clinical analyses, and the responsibilities of scientists, clinicians and chemical manufacturers to their clients and to society. Emphasis in this short report is on the assay of Ellman et al., in which thiocholine substrates are hydrolyzed by ChEs, and the released thiol groups react with the chromogen dithiobisnitrobenzoate (DTNB) to produce a yellow color (peak absorbance at 412 nm).

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