Evaluating Improvements to Exposure Estimates from Fate and Transport Models by Incorporating Environmental Sampling Effort and Landscape-level Contaminant Use

Abstract

AO_SCPCAPBSTRACTC_SCPCAPThe Pesticide in Water Calculator (PWC) is a fate and transport model used by the Environmental Protection Agency and Health Canada to estimate pesticide exposures in lentic freshwater ecosystems and make pesticide registration decisions. We leverage over 600,000 field measurements of 31 common insecticides and herbicides to test whether incorporating environmental sampling effort (number of times a pesticide is sampled) and landscape-level contaminant use (national application amount) can improve PWC validation and prediction, respectively. We found that maximum measured concentrations of 38% of herbicides and 42% of insecticides exceeded maximum estimated environmental concentrations (EECs) generated by the PWC, suggesting that EECs often do not represent worst-case exposure. For lentic systems, variance in pesticide field measurements explained by EECs increased by 50% when sampling effort was included. For lotic systems, variance explained increased by only 4%, most likely because lotic systems are sampled over 4.9 times as much as lentic systems. Including landscape-level use more than doubled the ability of the PWC to predict maximum pesticides concentrations in lentic systems. Exposure characterization in risk assessment can be improved by including sampling effort in model validation and landscape-level use in predictions, thus providing more defensible environmental standards and regulations.\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=167 SRC=\"FIGDIR/small/472969_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (122K):\norg.highwire.dtl.DTLVardef@601b22org.highwire.dtl.DTLVardef@19591e5org.highwire.dtl.DTLVardef@9d6196org.highwire.dtl.DTLVardef@71c96c_HPS_FORMAT_FIGEXP M_FIG C_FIG