Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2013
Publication Date: 1/15/2014
Publication URL: http://handle.nal.usda.gov/10113/59808
Citation: Potter, T.L., Hapeman, C.J., Mcconnell, L.L., Harman-Fetcho, J.A., Schmidt, W.F., Rice, C., Schaffer, B. 2014. Endosulfan wet deposition in Southern Florida. Science of the Total Environment. 468-69, 505-513. http://dx.doi.org/10.1016/j.scitotenv.2013.08.070. Interpretive Summary: During and after their application some pesticides evaporate and are transferred to the atmosphere. Amounts depend on pesticide properties, use patterns, and climatic conditions. Once in the atmosphere, pesticides move with prevailing winds. Rain tends to strip pesticides from air resulting in their deposition on land surfaces. Adverse ecological consequences have been documented; thus to minimize risks of pesticide use measurements that determine the rate of pesticide wet deposition are needed. Measurements are critically important where crops are produced on land adjacent to sensitive natural areas. This is case in southern Florida. Around the city of Homestead, farmland used for intensive vegetable productions borders both the Everglades and Biscayne Bay National parks. Our studies conducted over 4 years focused on measuring the deposition rates of one widely used insecticide, endosulfan, in rainfall within the Homestead agricultural area in the two parks. The compounds and its principal degradation product were detected at high frequency in event-based rain samples. The highest concentrations and deposition rates were in samples collected within the agricultural area and at all sites during growing seasons. This supports the conclusion that the principal endosulfan source in rain samples was from local use. The relatively high deposition in the crop production area and frequency of observation at all sites of concentrations that exceeded aquatic life toxic effects thresholds indicated that endosulfan wet deposition has been and continues to be a significant threat to aquatic life in the region. In addition the high deposition measurements made near Homestead indicate that humid tropical and or sub-tropical climatic conditions that prevail in the area may be a strong driver in promoting endosulfan volatilization and re-deposition in rainfall. This emphasizes a need for further work with endosulfan and other semi-volatile pesticides where climatic may promote atmospheric transport and deposition.
Technical Abstract: The atmosphere is an important transport route for semi-volatile pesticides like endosulfan. Deposition, which depends on physical-chemical properties, use patterns, and climatic conditions, can occur at local, regional, and global scales. Adverse human and ecological impact may result. We measured endosulfan wet deposition in precipitation over a 4-yr period within an area of high agricultural use in Southern Florida (USA) and in nearby Biscayne and Everglades National Parks. Endosulfan’s two isomers and degradate, endosulfan sulfate, were detected at high frequency with the order of detection and concentration being ß-endosulfan > a-endosulfan > endosulfan sulfate. Within the agricultural area, detection frequency (55 to 98%) mean concentrations (5 to 87 ng L-1) and total daily deposition (200 ng m-2 day-1) exceeded values at other sites by 5 to 30-fold. Strong seasonal trends were also observed with values at all monitored sites significantly higher during peak endosulfan use periods when vegetable crops were produced. Relatively high deposition in the crop production area and observations that concentrations exceeded aquatic life toxicity thresholds at all sites indicated that endosulfan volatilization and wet deposition are of ecotoxicological concern to the region. This study emphasizes the need to include localized volatilization and deposition of endosulfan and other semi-volatile pesticides in risk assessments in Southern Florida and other areas with similar climatic and crop production profiles.