Characterizing and estimating pesticide degradation in food crops

Abstract

Background. Dissipation half-lives are an important driver for fate behavior of pesticides in food crops, but also among most uncertain parameters in exposure models. Hence, a proper estimation of half-lives in crops is required, but still not available. Aims. We aimed at providing a consistent framework for estimating pesticide half-lives in food crops for use in modeling approaches applied in human exposure assessments. Methods. We first build a database of 4518 measured pesticide dissipation half-lives, of which 41% have been measured in the last 5 years, mostly in Asia. Second, we determine the influence of temperature using a subset of 1011 data points with reported temperatures. Third, we calculate recommended geomean values of half-lives at 20°C and standard deviations on their log for 330 pesticides and 44 crops, using multiple imputations for missing temperatures. We finally propose a regression-based model to predict half-lives for other pesticides as a function of temperature, substance class, chemical properties and crop type. Results. Temperature is the major determinant of the variability of measured half-lives for a given pesticide. When temperature was also reported, the regression model is able to explain 69% of the variability as a function of crop, temperature and substance. Considering all data available, the model still explains 46% of the variability. Interestingly, the range of recommended geomean half-lives is relatively narrow, with the 2.5th and 97th percentiles across pesticides ranging from 0.9 to 21 days. Results of the predictive model show that when temperature is known, 56% of half-life variability can be explained by temperature, crop type, substance class, Kow and Koc. When substance class and crop are not considered in the model, the R² is reduced from 0.56 to 0.30 with molecular weight becoming significant. Conclusions. Our research has important implications for human exposure assessment, especially since food crop consumption is the predominant exposure pathway of the general public towards pesticides