Submitted to: International Congress of Pesticide Chemistry Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: April 30, 2002
Publication Date: August 4, 2002
The Chesapeake Bay is the largest estuary in the United States. Recently, significant regulatory actions have been implemented to protect air and water quality in the region. While reductions in nutrient loads are a major focus, another goal is to achieve a Bay free of toxics. This project was designed to reveal temporal trends in atmospheric deposition fluxes in a highly agricultural watershed in the Chesapeake Bay system (the Choptank River) and determine the contribution of atmospheric processes as a source of pesticides to the watershed. Surface water, air and rain samples were collected frequently from May to December, 2000 and were analyzed for a number of commonly used pesticides. Metolachlor, atrazine, simazine, chlorothalonil, endosulfan and chlorpyrifos were frequently detected in air and rain. Metolachlor concentrations in the gas-phase ranged from 72 pg m-3 to a maximum of 10,000 pg m-3, and in rain the highest concentration was 1000 ng L-1 on May 19, 2000 declining to below quantification limits (3.6 ng L-1) in late August. Chlorothalonil had the second highest maximum concentration in air with a median concentration of 230 pg m-3, and was also frequently detected in rain ranging from 12 to 2000 ng L-1. A maximum concentration of 680 pg m-3 for a-endosulfan was found on 18 July, 2000. In rain, a-endosulfan was only observed in the summer with a maximum concentration of 31 ng L-1 on 14 July. Compared to the mass applied in the watershed, the loads deposited by rain were small for herbicides (<1%) and organophosphate insecticides (<0.05%), but the total mass of chlorothalonil deposited by rain over the entire watershed(approximately 150 kg) represents 13% of applied material. Fourteen percent of the annual amount of a-endosulfan applied and 90% of b-endosulfan were deposited by rain back to the watershed. These results suggest a regional atmospheric transport source from the southern Chesapeake Bay in Virginia, where large areas of tomatoes are grown and chlorothalonil and endosulfan are heavily used.