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Title: WET DEPOSITION AND AIR-WATER GAS EXCHANGE OF CURRENTLY USED PESTICIDES TO A TRIBUTARY OF THE CHESAPEAKE BAY

Author
item Harman Fetcho, Jennifer
item McConnell, Laura
item BAKER, JOEL - U MD-CES SOLOMONS
item Rice, Clifford

Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: The Chesapeake Bay estuarine drainage area receives the highest pesticide application of any coastal area in the US., however, large gaps exist in information on pesticide residues entering Chesapeake Bay tributaries. The shallow nature of the Chesapeake Bay makes it vulnerable to both runoff and atmospheric inputs of theses potentially toxic chemicals. The goal of this sproject was to determine the amount of agricultural pesticides which enter the central Chesapeake Bay region by rain fall and gas exchange between the air column and surface waters. Rain, air and surface water samples were collected from April 17 to July 20, 1995 at the mouth of the Patuxent River in Solomons, MD. These samples were analyzed for sixteen commonly used pesticides. Of the sixteen pesticides studied, the fungicide, chlorothalonil, had the highest maximum air concentration at 6.8 ng/m3. Maximum rain deposition measurements were highest for methyl parathion, malathion, metolachlor, and atrazine. Air-water gas exchange amounts calculated for chlorpyrifos and metolachlor ranged from -20 to 68 ng/m2-d and -41 to -0.05 ng/m2-d, respectively with negative values indicating net movement of the compound from the air to the surface water and positive values indicating volatilization from the water to the air column. The major transfer direction for the insecticide chlorpyrifos was from water to air while for the herbicide metolachlor, the direction was from air into the surface waters. The total rain deposition load was 310 and 7500 ng/m2, respectively for chlorpyrifos and metolachlor during the study period with a net gas exchange loss of chlorpyrifos of 290 ng/m2, and a net gain of metolachlor of 260 ng/m2.

Technical Abstract: The shallow nature of the Chesapeake Bay makes it vulnerable to both runoff and atmospheric inputs of potentially toxic chemicals. The project goal was to determine gas exchange and wet deposition fluxes of agricultural pesticides in the central Chesapeake Bay region. Rain, air, and surface water samples were collected from April 17 to July 20, 1995 at the mouth of fthe Patuxent River in Solomons, MD. Of the sixteen pesticides studied, chlorothalonil had the highest maximum air concentration at 6.8 ng/m3. Maximum wet deposition flux measurements were highest for methyl parathion, malathion, metolachlor, and atrazine. Air-water gas exchange fluxes calculated for chlorpyrifos and metolachlor ranged from -20 to 68 ng/m2-d and -41 to -0.05 ng/m2-d, respectively with negative values indicating net gas absorption. The major equilibration transfer direction for chlorpyrifos was from water to air while for metolachlor the direction was from air into the surface waters. The total wet deposition load was 310 and 7500 ng/m2, respectively for chlorpyrifos and metolachlor during the study period with a net gas exchange loss of chlorpyrifos of 290 ng/m2, and a net gain of metolachlor of 260 ng/m2.