CHLORPYRIFOS IN THE AIR AND SURFACE-WATER OF CHESAPEAKE BAY - PREDICTIONS OF ATMOSPHERIC DEPOSITION FLUXES

A 1993 survey including eight stations down the center of the Chesapea ke Bay mainstem, four times during the year, resulted in detection of chlorpyrifos in 100% of air and water samples. Water concentrations we re higher in March and April, coinciding with the spring flush from th e Susquehanna River (1.67-0.25 ng L-1). The lowest water concentration s were found in September (0.25-0.045 ng L-1). Air concentrations were lowest in March (2-3 pg m(-3)). Air concentrations were highest in Ju ne in the southern Bay region (95 pg m(-3)). Atmospheric loadings of c hlorpyrifos to the Chesapeake Bay mainstem were estimated for the four sample collection periods using fugacity-based equations. Net volatil e loss of chlorpyrifos across the surface area of the Bay was predicte d in March and April at 147 and 145 g day(-1), respectively, while net deposition was predicted for June and September at 85 and 56 g day(-1 ), respectively. A comparison of atmospheric loadings to the Bay with total load within the surface water illustrates that, during the mid t o late summer, atmospheric loadings become an important contributor to the Bay chlorpyrifos budget.