Association between indoor residential contamination with methyl parathion and urinary para-nitrophenol

Methyl parathion, a pesticide listed by the U.S. Environmental Protection Agency in Toxicity Category I (i.e., most toxic), is not licensed for indoor use, and human exposure has resulted in the deaths of infants and children. From January 1991 through November 1994, an unlicensed pesticide applicator sprayed the interior of more than 200 homes in Lorain County, Ohio, with methyl parathion. To measure the environmental contamination this spraying caused, we measured methyl parathion in residential samples (air filtration and surface wipe) collected from a subset of 64 homes. To measure human exposure, we collected urine samples from 142 people living in these homes and measured urinary levels of para-nitrophenol, a methyl parathion metabolite. We then used a generalized estimating equation to evaluate the association between residential contamination and human exposure. The model included the age of the resident, the number of days between pesticide application and sample collection, and air and surface-wipe methyl parathion concentrations. As expected, the air and surface-wipe concentrations each had a significant inverse relationship with the number of days between application and sample collection. The model explained 65.7% of the variation in urinary para-nitrophenol concentrations. The form of this model could be used to estimate urine p-nitrophenol in residents exposed to methyl parathion in situations where urine specimens are not available. We recommend site-specific validation of this model.