Diffusional Fluxes of Pharmaceutical and Personal Care Products Across the Sediment-Water Interface in the Urban Tidal Freshwater Potomac River (Washington, DC)

Pharmaceutical and personal care product (PPCPs) chemicals represent emerging contaminants in surface waters and sediments. An important source of PPCPs in urban regions is wastewater discharge. The sediment-water fluxes of PPCPs in the tidal freshwater Potomac River in the Washington, DC region were evaluated using a boundary layer model to better understand the source-sink dynamics of PPCPs in tidal estuaries. PPCPs were measured in sediments, water and pore water in the TFWPR along a downstream transect starting near a local high capacity wastewater treatment facility. PPCP quantification in the river samples was performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the results were used to populate a boundary layer model: F=K_L(C_pw - C_w), where F is flux (ng/m²-s), K_L is a overall mass transport coefficient (m/s), C_pw is the measured porewater concentration of PPCP (ng/m³), and C_w is the overlying water column concentration of PPCP (ng/m³). The mass transport coefficients incorporated water (only), colloid (as dissolved organic carbon associated PPCP) and bioturbation terms in the model. The flux estimates for 22 selected PPCPs showed that the flux direction of PPPs was entirely water-to-sediment in the vicinity of WTP discharge, whereas downstream locations (further away from WTP discharge) showed sediment-to-water fluxes of the PPCPs. Sediment-water fluxes were evaluated by measuring the concentrations of selected PPCPs in sediments, pore water and overlying water and applying the measurements in a Te observations imply that sediments serve as both sinks and sources along the river continuum. It appears PPCPs flux into and out of sediments depending on distance from the discharge point in the river.