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Title: ATMOSPHERIC DEPOSITION OF PESTICIDES TO AN AGRICULTURAL WATERSHED OF THE CHESAPEAKE BAY

Author
item KUANG, Z - UNIV. OF MARYLAND
item McConnell, Laura
item TORRENTS, ALBA - UNIV. OF MARYLAND
item MERITT, D - UNIV. OF MARYLAND
item TOBASH, S - UNIV. OF MARYLAND

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2003
Publication Date: 9/1/2003
Citation: Kuang, Z., McConnell, L.L., Torrents, A., Meritt, D., Tobash, S. 2003. Atmospheric deposition of pesticides to an agricultural watershed of the Chesapeake Bay. Journal of Environmental Quality. 32:1611-1622.

Interpretive Summary: The Choptank River watershed, located on the Delmarva Peninsula of the Chesapeake Bay, is dominated by agricultural land use which makes it vulnerable to runoff and atmospheric deposition of pesticides. Agricultural and wildlife areas are in close proximity, and off-site losses of pesticides may contribute to toxic impacts on sensitive species of plants and animals. In order to determine atmospheric inputs of pesticides to this watershed, air and rain samples were collected throughout 2000, and surface water samples from the estuary were collected on five occasions. Chlorothalonil, metolachlor, atrazine, simazine, endosulfan and chlorpyrifos were frequently detected in the air and rain at low levels (<1 part-per-billion), with maximum levels during the period when local or regional crops were planted. Pesticide loads to the watershed from precipitation are estimated at 150+/-16, 61+/-7, and 51+/-6 kg/yr for chlorothalonil, metolachlor, and atrazine, respectively. The high wet deposition load compared to the estimated annual usage for chlorothalonil (13%) and endosulfan (14-90%) suggests an atmospheric source from outside the watershed. This project does suggest that the atmosphere responds rapidly to pesticide use both inside and outside the Choptank watershed. While atmospheric inputs are not as intense as runoff loads to the river, the atmosphere is a continuous diffuse source of pesticides to every surface in the watershed.

Technical Abstract: The Choptank River watershed, located on the Delmarva Peninsula of the Chesapeake Bay, is dominated by agricultural land use which makes it vulnerable to runoff and atmospheric deposition of pesticides. Agricultural and wildlife areas are in close proximity, and off-site losses of pesticides may contribute to toxic impacts on sensitive species of plants and animals. High-volume air samples (n=31) and event based rain samples (n=71) were collected from a single location in the watershed representing regional background conditions. Surface water samples were collected from eight stations in the tidal portion of the river on five occasions during 2000. Chlorothalonil, metolachlor, atrazine, simazine, endosulfan and chlorpyrifos were frequently detected in the air and rain, with maximal concentrations during the period when local or regional crops were planted. The wet deposition load to the watershed was estimated at 150+/-16, 61+/-7, and 51+/-6 kg/yr for chlorothalonil, metolachlor, and atrazine, respectively. The high wet deposition load compared to the estimated annual usage for chlorothalonil (13%) and endosulfan (14-90%) suggests an atmospheric source from outside the watershed. Net air-water gas exchange fluxes for metolachlor varied from - 44+/-19 to 9.3+/-4.1 ng/m2-d with negative values indicating net deposition. Wet deposition accounted for 3-20% of the total metolachlor mass in the River and was a more important source to the river than gas exchange. Estimates of herbicides flux presented here are likely a low estimate and actual rates may be significantly higher in areas closer to pesticide application.