Pesticides urinary metabolites

Applicators, mixers, loaders, and others who mix, spray, or apply pesticides to crops face potential dermal and/or inhalation exposure when handling bulk quantities of the formulated active ingredients. Although the exposure periods are short and occur only a few times annually, an estimate of this exposure can be obtained by quantifying the excreted polar urinary metabolites. Atrazine is the most studied triazine for potential human exposure purposes, and, therefore, most of the reported methods address the determination of atrazine or atrazine and its metabolites in urine. To a lesser extent, methods are also reported for the analysis of atrazine in blood plasma and serum. 

Davies, J.E., Enos, H.F., Barquet, A., Morgade, C., and Danauskas, J.X. (1979) Developments in toxicology and environmental sciences pesticide monitoring studies. The epidemiologic and toxicologic potential of urinary metabolites, in Toxicology and Occupational Medicine, Deichman, W.B., Ed., pp. 369-380. 

A report entitled Chemical Trespass was issued in May 2004 by the Pesticide Action Network (Schafer et al., 2006). It contained detailed analysis of 2000/01 National Health and Nutrition Examination Survey (NHANES) OP urinary metabolite data and used published methods to estimate exposure levels to parent compounds from creatinine corrected urinary metabolite levels. They focused on chlorpyrifos and its metabolite 3,4,6-trichloro-2-pyridinol (TCP), and found that chlorpyrifos exposures for children ages 6-11 and 12-19 exceeded EPA s chronic population-adjusted dose (cPAD) by surprisingly wide margins. Geometric mean TCP levels were 3 to 4.6 times higher than the EPA-estimated safe dose, as shown in Fig. 14.2. The more heavily exposed children received daily doses more than ten times the safe level. 

Chlorpyrifos provides an example of the utility of human pharmacokinetic models to estimate daily dose from biomonitoring data for a rapidly cleared pesticide. The urinary metabolite trichloro-2-pyridinol (TCP) is used in the NHANES study to monitor population exposure to chlorpyrifos (CDC 2005). Several epidemiologic studies have linked chlorpyrifos exposure to adverse birth outcomes through associations between urinary and blood biomarkers and have demonstrated maternal exposure and physiologic measurements in the neonate (Berkowitz et al. 2003, 2004 Whyatt et al. 2004 Needham 2005). 

Tissues such as fat, blood or liver can be examined for residues of the more stable chlorinated hydrocarbon pesticides. In most cases these tissues are available as a result of elective survery, autopsy or biopsy. Exposure to DDT results in some storage of the parent compound in body fat. A large portion, however, is metabolized and stored as DDE (jJ). Aldrin and hepta-chlor are similarly transformed and stored as dieldrin and hepta-chlor epoxide. Levels of the urinary metabolite DDA have been used to assess exposure or body burden of DDT (10, 11, 12). Hexachlorobenzene and the various isomers of hexachlorocyclo-hexane are stored in fat as the parent compound but a small... 

Several approaches to the measurement of respiratory exposure are available. The first was developed by Durham and Wolfe ( ) and employs a respirator with the collection pads protected by cones from direct spray. The second common method uses the personal air sampler with a pump carried by the worker and a collection device In the general breathing zone. The third method involves a more careful experimental design. In this case, the worker wears a pesticide respirator for a certain period of time with the respirator removed for an equal amount of time. Twenty-four hour urine samples are collected each day, with any observed Increase in urinary metabolites Indicating the degree of respiratory exposure. 

The exposure pad method, combined with measurement of urinary metabolites, has been used to compare worker exposure for different pesticide application methods (33, 34) as well as to monitor formulating plant worker exposure (35) and homeowner exposure (36). 

We return, consequently, to the problem of the excretion kinetics of pesticides, the complexity of which may render useless any search for a simple linear correlation between dose and urinary metabolites. Some experimenters have attempted to Investigate this area. Drevenkar et al. (20) studied the excretion of phosalone metabolites In one volunteer. Excretion reached a peak In 4-5 hr., but was not complete In 24 hr. Funckes et al. (42) exposed the hand and forearm of human volunteers to 2% parathlon dust. During exposure, the volunteers breathed pure air and placed their forearm and hand Into a plastic bag which contained the parathlon. This exposure lasted 2 hr. and was conducted at various temperatures. There was an Increased excretion of paranltrophenol with Increasing exposure temperature. More importantly, paranltrophenol could still be detected In the urine 40 hr. post exposure. In another human experiment, Kolmodln-Hedman et al. (43) applied methychlorophenoxy acetic acid (MCPA) to the thigh. Plasma MCPA reached a maximum in 12 hr. and MCPA appeared In the urine for 5 days with a maximum after about 48 hr. Given orally, urinary MCPA peaked in 1 hr. with about 40% of the dose excreted In 24 hr. In a rat experiment, seven different organophosphates at two different doses were fed to two rats per compound (21). The rats were removed from exposure after the third day and blood and urine collected for the next 10 days. 

The process whereby pesticides are registered In Canada Is not unlike that In many other countries. The manufacturer Is required under Federal law to submit, at the time of application for registration, a package of data supporting the safety and efficacy of the product. If after review of these data, the product Is judged to be acceptable. It Is registered and food tolerances are established If required. Over the past 5 years there has been an Increased awareness of the potential health hazards to those Involved In the application of pesticides and those Inadvertently exposed during application (bystanders). To properly analyze these risks, more accurate estimates of exposure are essential. The problems associated with current methods of exposure, the Importance of analysis of urinary metabolites, Che correlation of dermal exposure and urinary metabolites and the determination of percutaneous penetration are discussed. 

The detection of pesticide metabolites in the urine of workers indicates prior exposure. However, it is difficult to relate this level of urinary metabolite to the actual worker exposure, and it is equally difficult to Interpret the toxicological significance of the level. A preliminary study conducted in rats exposed dermally to 100, 200 and 400 ug of azinphos-methyl showed a significant linear correlation between the dermal dosage and the urinary alkyl phosphate metabolite levels (19). Further studies are being conducted in other species to determine whether a similar type of relationship occurs and to develop a standard curve in which urinary metabolite levels could be utilized to estimate the amount of dermal exposure. 

The actual biological monitoring of workers to detect evidence of exposure such as a drop in blood cholinesterase levels or the presence of a urinary metabolite is superior to the indirect techniques employed in this study. Realizing the difficulties in accurately determining the dermal exposures of mixers, loaders, and applicators to pesticides, the employment of simpler monitoring techniques than the ones performed by CDFA in this report might... 

Methyl 5-hydroxy-2-benzimidazole carbamate (MHBC, Figure 7.4), a urinary metabolite of the pesticides carbendazium, benomyl and thiophanate-methyl, has been measured using an ODS-modihed silica analytical column with methanol-aq. ammonium acetate (approximately 60 mmol L , pH 8) (27 + 73) as eluent and ED (PGE, +0.22 V vs Pd). Sample preparation was by a complex procedure involving SPE (SCX-modified silica) of hydrolysed specimens. No internal standard... 

Urinary metabolites produced from gamma- and beta-BHC in the mouse Chloro-phenol conjugates. Pesticide Biochem. Physiol. 4, 220 (1974). 

In two cases of moderate intoxication from mevinphos, urinary excretion of dimethylphos-phate (a metabolite of mevinphos) was almost complete 50 hours after exposure/ Although a number of other organophosphorus pesticides also yield dimethyl phosphate, the presence of significant amounts of this metabolite in the urine may be useful in estimating the absorption of mevinphos. 

In addition to these calculated estimates of absorption, a specific estimate of absorbed dose can be made by measuring the metabolites of the pesticide in urine. For pesticides on which good data exist on metabolic excretion, it appears that this method is very sensitive. In a study conducted on orchardists (7), metabolites were detected in the urine samples of all workers, and a statistically significant correlation was found between the total 48 hour metabolite output and the total amount of pesticide sprayed. In contrast the same study indicated that the correlation between urinary output and the total spray time was not significant. This supports the point mentioned earlier that it seems reasonable to presume that exposure is related to the total amount available for contact, and that correlating exposure with the spray time may be misleading. 

Examination of tissues and excreta from humans or animals for exposure to carbamate pesticides, will almost never result in detection of the parent compound. Exposure assessment of this nature requires determination of metabolitic products, except in extreme situations such as acute poisoning. The most widely used indicator of exposure is probably the determination of urinary phenols (9). 

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