Correlating Agricultural Use with Ambien Air Concentrations of Methyl Bromide During the Period of 2011-2014.
Abstract
The Department of Pesticide Regulation (DPR) collected 24-hour samples each week to measure ambient air concentrations of 37 chemicals including methyl bromide in three California communities (Shafter, Ripon, and Salinas) for its air monitoring network (AMN) from 2011 to 2014. In addition, DPR collected pesticide use information through its pesticide use reporting (PUR) database during the same time period. A linear regression model was built that compared ambient methyl bromide concentrations to methyl bromide applications made within one to five miles of the Salinas and Ripon AMN stations. The model took into account spatial and temporal variables into the regression analysis.
We found that methyl bromide concentrations detected by the Salinas AMN station were moderately correlated (r2 = 0.47) with agricultural methyl bromide applications made within five miles. AMN detections of methyl bromide at the Ripon AMN station were poorly correlated (r2 = 0.11) with agricultural applications made within five miles. High frequency of non-detectable concentrations of methyl bromide at the Shafter AMN station prevented statistical analysis. The results suggest that additional factors may account for a majority of the variation in AMN detected methyl bromide concentrations. The limitations of the linear regression model and likely confounding factors such as non-agricultural methyl bromide use, meteorological conditions, and application methods are discussed.