Wet deposition and air-water gas exchange of currently used pesticides to a subestuary of the Chesapeake Bay

The shallow nature of the Chesapeake Bay makes it vulnerable to bath runoff and atmospheric inputs of anthropogenic chemicals. The project goal was to determine agricultural pesticide concentrations in air and rain and to calculate gas exchange fluxes to a Chesapeake Bay subestuary. Rain, air, and surface water samples were collected from April 17 to July 2, 1995 from the Chesapeake Biological Laboratory research pier in Solomons, MD. Of the 16 pesticides studied, chlorothalonil had the highest maximum air concentration (6.8 ng/m(3)). Maximum wet deposition flux measurements were highest far methyl parathion (3.4 mu g/m(2)-d), malathion (1.8 mu g/m(2)-d), metolachlor (1.3 mu g/m(2)-d), and atrazine (1.3 mu g/m(2)-d). Air-water gas exchange fluxes calculated for chlorpyrifos and metolachlor ranged from -20 to 68 ng/m(2)-d and -41 to -0.05 ng/m(2)-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 -210 and -7100 ng/m(2), respectively, for chlorpyrifos and metolachlor during the study period with a net gas exchange loss of chlorpyrifos of 290 ng/m(2) and a net gain of metolachlor of -260 ng/m(2).