Correlating Agricultural Use with Ambient Air Concentrations of Chlorpyrifos And Chlorpyrifos-Oxon During the Period of 2011-2014
Abstract
The Department of Pesticide Regulation’s (DPR) Air Monitoring Network (AMN) collected 24-hour samples each week to measure ambient air concentrations of 37 chemicals including chlorpyrifos and its breakdown product chlorpyrifos-oxon in three California communities (Shafter, Ripon, and Salinas) from 2011 to 2014. In addition, DPR collected pesticide use information through its Pesticide Use Reporting (PUR) database for the same time period. A linear regression model was built that compared chlorpyrifos applications made within one to five miles of the AMN station to ambient air concentrations of chlorpyrifos and chlorpyrifos-oxon. The model took into account applications made during the 24-hour AMN monitoring period and up to three days prior as well as application method.
We found that quantitative and trace detections of chlorpyrifos and/or chlorpyrifos-oxon fluctuated based on the annual pounds of chlorpyrifos applied and that detections tended to occur seasonally during periods of high chlorpyrifos use. Additionally we observed that formulation type (liquid vs. granular), application method (aerial vs. ground), proximity of chlorpyrifos applications made to the AMN station, and the pounds of chlorpyrifos applied may influence the frequency and level of AMN detections. Overall we found that AMN detections of chlorpyrifos and chlorpyrifos-oxon at Shafter may be best explained by aerial applications made within one to two miles of the AMN station during the 24-hour sampling period. Our model was partially limited due to the high frequency of non-detections along with the inherent spatial, temporal, and meteorological variability between individual pesticide applications.