Submitted to: Proceedings of the X Symposium of Pesticide Chemistry: Environmental Fate
Publication Type: Abstract Only
Publication Acceptance Date: November 15, 1999
Publication Date: N/A
Technical Abstract: Agricultural activity has been implicated in the decline in water quality of the Chesapeake Bay. A large gap in information exists regarding the fate of agricultural pesticides used in the sub-watersheds of the Bay. Limited information on the timing and magnitude of pesticide usage, inadequate information on the amount of these chemicals moving into the tributaries, and the added complication that comes with predicting loads from tidal systems has made the quantification of pesticide loads to the Chesapeake Bay a difficult task. In this project, studies of spatial and temporal variations in pesticide concentrations of two tributaries within this system, the Patuxent and Choptank Rivers, have been carried out. The major crops in both sub-watersheds are corn and soybeans, thus herbicides are the dominant chemicals used in these areas. Atrazine, 6-amino-2-chloro-4-isopropylamino-s-triazine (CIAT), metolachlor, cyanazine eand simazine were consistently observed in both rivers. Atrazine was present in the highest concentrations in both rivers with a maximum observed level of 1.2 ug/L and 0.9 ug/L in the Patuxent and Choptank Rivers, respectively. The maximum concentrations in both rivers were found at upstream, freshwater areas with declining concentrations with increasing salinity. Watershed characteristics such as land usage and soil types along with pesticide usage and river flow conditions are being combined to assess the retention of pesticides in the watershed. Profiles of pesticide concentrations down the river are being used to determine if dilution is the only important factor in the removal of these chemicals from the water column. This work will provide new information on the occurrence, behavior and fate of these chemicals in the estuarine systems of the Chesapeake Bay.