Academic journal article Environmental Health Perspectives

Neurologic Function among Termiticide Applicators Exposed to Chlorpyrifos

Academic journal article Environmental Health Perspectives

Neurologic Function among Termiticide Applicators Exposed to Chlorpyrifos

Article excerpt

Chlorpyrifos is a moderately toxic organophosphate pesticide. Houses and lawns in the United States receive a total of approximately 20 million annual chlorpyrifos treatments, and 82% of U.S. adults have detectable levels of a chlorpyrifos metabolite (3,5,6-trichloro-2-pyridinol; TCP) in the urine. The U.S. Environmental Protection Agency has estimated that there are 5,000 yearly reported cases of accidental chlorpyrifos poisoning, and approximately one-fourth of these cases exhibit symptoms. Organophosphates affect the nervous system, but there are few epidemiologic data on chlorpyrifos neurotoxicity. We studied neurologic function in 191 current and former termiticide applicators who had an average of 2.4 years applying chlorpyrifos and 2.5 years applying other pesticides, and we compared them to 189 nonexposed controls. The average urinary TCP level for 65 recently exposed applicators was 629.5 [micro]g/L, as compared to 4.5 [micro]g/L for the general U.S. population. The exposed group did not differ significantly from the nonexposed group for any test in the clinical examination. Few significant differences were found in nerve conduction velocity, arm/hand tremor, vibrotactile sensitivity, vision, smell, visual/motor skills, or neurobehavioral skills. The exposed group did not perform as well as the nonexposed group in pegboard turning tests and some postural sway tests. The exposed subjects also reported significantly more symptoms, including memory problems, emotional states, fatigue, and loss of muscle strength; our more quantitative tests may not have been adequate to detect these symptoms. Eight men who reported past chlorpyrifos poisoning had a pattern of low performance on a number of tests, which is consistent with prior reports of chronic effects of organophosphate poisoning. Overall, the lack of exposure effects on the clinical examination was reassuring. The findings for self-reported symptoms raise some concern, as does the finding of low performance for those reporting prior poisoning. Although this was a relatively large study based on a well-defined target population, the workers we studied may not be representative of all exposed workers, and caution should be exercised in generalizing our results. Key wordy, chlorpyrifos, neurotoxicity, organophosphates. Environ Health Perspect 108:293-300 (2000). [Online 18 February 2000] http://ehpnet1.niehs.nih.gov/docs/2000/108p293-300steenland/abstract.html

Chlorpyrifos (O, O-diethyl 0-3,5,6-trichloro-2-pyridyl phosphorothioate) is an organophosphate pesticide used in both agricultural and residential pest control. It exhibits moderate acute toxicity, readily inhibiting plasma cholinesterase at low doses and inhibiting red blood cell cholinesterase at high doses (1). Like all organophosphates, chlorpyrifos can cause acute poisoning; well-known symptoms include miosis, increased urination, diarrhea, diaphoresis, lacrimation, and salivation (2).

Chlorpyrifos was first marketed in 1965. Its use has increased rapidly, in part due to the banning of chlordane for termite applications in 1988. The principal manufacturer of chlorpyrifos (Dow Elanco, Indianapolis, IN) has estimated that chlorpyrifos-containing products are applied in and around American homes more than 20 million times a year (3). In a survey of a random sample of U.S. adults (n = 929) conducted in the late 1980s and early 1990s, Hill et al. (4) estimated that detectable levels of a metabolite of chlopyrifos (3,5,6-trichloro-2-pyridinol; TCP) are present in the urine of 82% of U.S. adults, with a mean level of 4.5 [micro]g/L. TCP is largely specific for chlorpyrifos, although two other less common pesticides, chlorpyrifos-methyl and triclopyr, can also be metabolized to TCP. Agricultural use of chlorpyrifos is also common, accounting for about two-thirds of chlorpyrifos sales (5).

U.S. Environmental Protection Agency (HPA) investigators summarized chlorpyrifos poisoning data based on reports from poison control centers and concluded that "chlorpyrifos is one of the leading causes of acute insecticide poisoning incidents in the United States (6). …

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