Development of an environmental fate model for risk assessment of ultra-low-volume insecticides

Abstract

One of the most effective ways of managing adult mosquitoes that vector human and animal pathogens is the use of ultra-low-volume (ULV) insecticides. The U.S. Environmental Protection Agency uses models that are not validated for ULV insecticide applications and exposure assumptions to perform their human and ecological risk assessments. Currently, there is no validated model that can accurately predict deposition of insecticides applied using ULV technology for adult mosquito management. In addition, little is known about the deposition and drift of small droplets like those used under conditions encountered during ULV applications. The objectives of my dissertation were to perform field studies to measure environmental concentrations of insecticides and to develop a validated model to predict the deposition of ULV insecticides, and use the data generated from the field study to perform refined human and aquatic ecological risk assessments. To model the field data collected during the summers of 2009-2011 a regression model selected by the Bayesian Information Criterion and k-fold cross validation was used to validate the selected model. k-fold cross validation demonstrated that the mean square error and mean square prediction error were similar indicating good predictive ability. The human-health risk assessment demonstrated that previous risk assessments used conservative exposure scenarios that overestimated risks, thus being conservative in protecting human health. Our results demonstrated a 10-fold reduction in the RQ estimates when comparing risk assessments using estimated environmental concentrations and actual environmental concentrations from the environmental fate model. Because I used a large data set to model concentrations deposited on surfaces, this variance in exposure is due to the inherent variability in deposition concentrations after ULV applications and, therefore, would not warrant further refinement to improve risk assessments. The aquatic risk assessment using actual environmental concentrations showed that the 95th percentile estimated concentration would result in less than 0.0001% of the potentially affected fraction of species reaching their respective LC50. Our results are supported by the weight of evidence that pyrethroids applied by ground-based ULV applications will not result in deleterious effects on aquatic organisms.