Refinements in acute dietary exposure assessments for chlorpyrifos

Food pesticide residue data are used by the U.S. Environmental Protection Agency (EPA) to determine potential dietary risk from chronic and acute exposures. An acute dietary risk assessment determines the pesticide exposure resulting from a single-day consumption of food, and uses stepwise refinement of residue estimates to better judge actual exposures. All exposure refinements use estimates of the fraction of crops treated and food residues measured increasingly closer to the point of actual food consumption, without changes in the pesticide uses. Exposure distributions at all levels of data refinement were extremely right skewed. At the highest level evaluated, estimated exposures at the 99.9th percentile were 0.00087 mg/kgBW/day compared to 0.2648 mg/kgBW/day at the tolerance level for children 1-6 years, theoretically the highest-exposed population sub-group. The estimated exposure at the 99.9th percentile of the U.S. population was approximately twice the exposure at the 99th percentile and 33 times the exposure at the 90th percentile. This evaluation showed the calculated exposure at the highest tier of assessment was 300 times lower than the tolerance level assessment for children 1-6 years at the 99.9th percentile. Reduction in exposure estimates between these tiers was due to a combination of the following factors: food residue measurements in a specially designed market-basket study, government-sponsored monitoring data, probabilistic methodologies, market share information, and food processing data. This case study demonstrates that an improved understanding of the uncertainties of acute dietary exposure from pesticides is possible by using well-established statistical tools and applying them to comprehensive exposure information, including residue monitoring data, consumption data, and pesticide use information.