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 Chesapeake Bay mainstem, four times during the year, resulted in detection of chlorpyrifos in 100% of air and water samples. Water concentrations were higher in March and April, coinciding with the spring flush from the Susquehanna River (1.67−0.25 ng L-1). The lowest water concentrations 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 June in the southern Bay region (95 pg m-3). Atmospheric loadings of chlorpyrifos to the Chesapeake Bay mainstem were estimated for the four sample collection periods using fugacity-based equations. Net volatile loss of chlorpyrifos across the surface area of the Bay was predicted 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 to late summer, atmospheric loadings become an important contributor to the Bay chlorpyrifos budget.