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Improved rapid analytical method for the urinary determination of 3,5,6 trichloro-2-pyridinol, a metabolite of chlorpyrifos.

MacKenzie BA; Striley CAF; Biagini RE; Stettler LE; Hines CJ
Bull Environ Contam Toxicol 2000 Jul; 65(1):1-7
Urinary immunoassays have been used as screens for occupational exposure to a variety of compounds, including pesticides (Feng et al. 1994; Biagini et al. 1995; Mastin et al. 1998). Immunoassays are generally quite sensitive, specific and accurate. However, biotransformation of xenobiotics may lead to urinary excretion of metabolites, which, in some cases, may lead to modulation of immunoreactivity yielding an over/under estimation of apparent body burdens, presumably from enhanced/inhibited competition by metabolic conjugates (Biagini et al. 1995). Hence, immunoassays for biological monitoring must be carefully evaluated to identify potential interferences from conjugates and other metabolites. Our laboratory is currently investigating immunochemical biological monitoring methods for various organophosphate pesticides. Of particular interest is a method for chlorpyrifos (CP - Figure 1 [A]), which is used to control a broad-spectrum of insects in the home and in agriculture. CP is one of the most widely used insecticides in the United States, with approximately 9-13 million pounds applied for crop protection and 2-4 million pounds applied for nonagricultural uses in 1995 (U.S. EPA 1997). Studies in channel catfish (Barron et al. 1991) and rats (Nolan et al. 1987) have shown the major urinary metabolite of CP to be the glucuronide conjugate (Figure 1 [B]) of 3,5,6- trichloro-2-pyridinol (TCP- Figure 1[C]). Urinary TCP has been used as the marker of exposure in studies investigating occupational and non-occupational exposures to CP (Fenske and Elkner 1990; Chang et al. 1996; Nolan et al. 1984 ). Acid hydrolysis has been used to liberate TCP from urine conjugates for subsequent urinary determinations by gas chromatography (Fenske and Elkner 1990; Nolan et al. 1984), gas chromatography-negative ion chemical ionization mass spectrometry (Ormand et al. 1999), high performance liquid chromatography (Chang et al. 1996) and immunoassay (Shackelford et al. 1999). Recovery of TCP has been shown to be increased in urine samples incubated with glucuronidase, suggesting that humans, like rats, excrete TCP as a glucuronide (Nolan et al. 1984). Enzymatic hydrolysis with b-glucuronidase was used by Hill et al. (1995) in conjunction with GC/MS/MS to measure 12 pesticide residues, including TCP, in urine. While a 17 hour b-glucuronidase incubation at 37 C was used by Hill et al. (1995) a study by Simonsson, et al. (1995) indicated that a much shorter incubation time (at least 30 min) at room temperature was successful in increasing the sensitivity of an immunoassay for urinary benzodiazepine without reducing the specificity of the method. In the present investigation, we describe a method using b-glucuronidase treatment of urine from individuals occupationally exposed to CP and a simple particlebased immunoassay. This method yields results correlating extremely well with a more elaborate, multi-step conventional method, acid hydrolysis followed by analysis for TCP by gas chromatography with mass selective detection (GC-MSD).
Analytical-Method; Occupational-exposure; Pesticides; Metabolites; Biological-monitoring; Laboratory-testing; Insecticides; Laboratory-animals; Animals; Animal-studies; Gas-chromatography; Mass-spectrometry
Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Division of Applied Research and Technology, 4676 Columbia Parkway, Cincinnati, OH 45226
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Bulletin of Environmental Contamination and Toxicology
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division