An Updated Algorithm for Estimation of Pesticide Exposure Intensity in the Agricultural Health Study

Abstract

An algorithm developed to estimate pesticide exposure intensity for use in epidemiologic analyses was revised based on data from two exposure monitoring studies. In the first study, we estimated relative exposure intensity based on the results of measurements taken during the application of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) (n = 88) and the insecticide chlorpyrifos (n = 17). Modifications to the algorithm weighting factors were based on geometric means (GM) of post-application urine concentrations for applicators grouped by application method and use of chemically-resistant (CR) gloves. Measurement data from a second study were also used to evaluate relative exposure levels associated with airblast as compared to hand spray application methods. Algorithm modifications included an increase in the exposure reduction factor for use of CR gloves from 40% to 60%, an increase in the application method weight for boom spray relative to in-furrow and for air blast relative to hand spray, and a decrease in the weight for mixing relative to the new weights assigned for application methods. The weighting factors for the revised algorithm now incorporate exposure measurements taken on Agricultural Health Study (AHS) participants for the application methods and personal protective equipment (PPE) commonly reported by study participants.

Pesticide use and risk of end-stage renal disease among licensed pesticide applicators in the Agricultural Health Study

“…Whereas prior studies were limited by small sample size and exposure to few chemicals, the large size of the AHS cohort allowed us to assess exposure-response trends for many individual pesticides. Also, use of a validated exposure-intensity metric25 allowed for a better estimate of each participant's likely pesticide exposure as opposed to non-specific pesticide use. Until now, the relationship between short-term high-level pesticide exposures and kidney disease has been evaluated only with respect to the immediate effects of pesticide poisonings.…”

“…Duration and frequency of use data were obtained on the take-home questionnaire for 28 additional pesticides. For each pesticide, an intensity-weighted lifetime exposure metric was generated by multiplying lifetime-days of use (product of duration and frequency of use) by an intensity score that accounts for differences in exposure resulting from variation in pesticide application methods, repair of pesticide application equipment, and use of personal protective equipment 25. The intensity score algorithm was developed using AHS-specific pesticide exposure monitoring data, in conjunction with expert judgment from published studies on pesticide exposure, including information from the Pesticide Handlers Exposure Database 25.…”

Pesticide use and incident hyperthyroidism in farmers in the Agricultural Health Study

“…A take-home questionnaire asked about duration and frequency of use for the remaining 28. Responses to questions about pesticide use practices were used to create exposure intensity weights 8. We multiplied duration and frequency of use to obtain lifetime days of use for each pesticide which was then weighted by exposure intensity to obtain intensity-weighted lifetime days (IWLDs) of use.…”

Cancer incidence and metolachlor use in the Agricultural Health Study: An update

“…These factors were modified since the previous analyses of metolachlor to incorporate refinements based on field measurement data for subgroups of the AHS population, resulting in minor changes to the intensity-weighted lifetime days. 7 In addition, analyses included a data-driven multiple imputation for days of use for applicators who did not complete the 1999–2005 questionnaire. 15 …”

“…These analyses saw weaker associations with intensity-weighted lifetime days, a metric that accounts for exposure-modifying factors. 7 Associations between metolachlor use and incidence of a number of other cancers were also examined in the prospective study. 6 The study found a decreasing risk of prostate cancer with increasing lifetime days of reported use.…”