Sediment–Water Distribution and Benthic Boundary Layer Fluxes of Pharmaceuticals and Personal Care Products near Wastewater Discharge into a Tidal River Shoal

Pharmaceuticals and personal care products (PPCPs) were measured in porewater, sediment, and surface water at three sites near wastewater treatment plant (WTP) discharge along a 2 km downstream transect in a tributary shoal embayment (Alexandria, VA) of the tidal Potomac River. A benthic diffusion layer model evaluated water-only, dissolved organic carbon (DOC)-associated, and bioturbation mass transport pathways. Fluxes of 17 PPCPs nearest the WTP were all in the direction of surface water to sediment porewater (negative) with magnitudes of −0.0016 to −7.4 ng m^–2 s^–1. At the next downstream site, fluxes of seven PPCPs were bidirectional (negative and positive) and ranged from −4.8 × 10^–4 to 0.0051 ng m^–2 s^–1. The furthest site downstream yielded fluxes of six PPCPs that were predominantly sediment to water (positive), ranging in magnitude from −0.0020 to 7.0 × 10^–4 ng m^–2 s^–1. The bioturbation and water-only mass transport coefficients contributed most to fluxes for PPCPs. The DOC-associated mass transport term was negligible. The fluxes indicated sediments will continue serve as a source of PPCPs 2 km downstream from WTP discharge.