PM13 Watershed/Airshed Science and Regulation
Exhibit Hall
8:00 AM - Monday, 10 November 2003
(PM194) Pesticides in the atmosphere over the Choptank River watershed, Chesapeake Bay.
Goel, A.1, McConnell, L.2, Torrents, A.1, Kuang, Z.1, Meritt, D.3, Tobash, S.3, 1 University of Maryland, College Park, Maryland, U.S.A.2 U.S. Department of Agriculture, Agricultural Research Services, Beltsville, Maryland, U.S.A.3 University of Maryland, Centre for Environmental Science, Cambridge, Maryland, U.S.a.
ABSTRACT- The Choptank river basin is an area of intense agricultural activity with 59% of the land in the watershed under cultivation with an estimated pesticide usage of 335 tons in 2000. Aerial deposition of pesticides used in the region may be an important source for the Choptank river and ultimately the Chesapeake Bay. Air and rain concentrations of pesticides were measured at one site in the Choptank River watershed from 2000-2002 (April-November). The highest concentrations of pesticides in air and precipitation were seen during the growing season from April to September. Chlorothalonil, metolachlor, a-HCH and a-endosulfan were detected in all air samples (n=31) in 2000 and chlordanes were present in quantifiable amounts in >85% of air samples. Clausius-Clapeyron plots for currently used pesticides reveal that temperature explains only 23-45% of the concentration variation in gaseous phase suggesting the strong influence of other factors such as local usage. In precipitation, chlorothalonil was the most abundant (35-46 % of total pesticide flux) and the most frequently detected compound. The largest fraction of the herbicide net flux was observed from April to June, while the insecticide flux depended on timing and amount of rainfall during the year. From 2000-2002 the net yearly wet fluxes of chlorothalonil and atrazine decreased by 32-41 % and 20-25%, respectively over the previous year's values while those of trifluralin increased by 40-100%. The total load of pesticides through wet deposition reduced from 176 ug/m in 2000 to 113 ug/m2 in 2002. The results indicate that the atmospheric concentrations of pesticides in the region are influenced by timing and pattern of usage as well as atmospheric conditions such as temperature and precipitation.
Key words: atmospheric transport, pesticides, wet deposition, herbicides