TRANSPORT OF PHARMACEUTICAL CHEMICALS IN ORGANIC- AND MINERAL-RICH SOILS

Pharmaceutical, active ingredients in personal care products (PhACs), and their derivative compounds are increasingly ubiquitous in surface waters across the world. Transport of three relatively common PhACs (naproxen, ibuprofen, and cetirizine) in different natural soils was measured. All of these compounds are relatively hydrophobic and have acid/base functional groups (naproxen and ibuprofen) and cetirizine is zwitterionic. The main goal of this study was to correlate organic matter (OM) and clay content in natural soils and sediment with sorption and transport of PhACs within the subsurface environment. Clean soils were collected from a pristine managed forested watershed near Charleston, South Carolina, USA, with no apparent sources of anthropogenic contamination. These soils had varying OM content between 0.4-9%, clay mineral content between 6-20%, and soil pH between 4.5-6. The A-horizon soils had higher OM and lower clay content than the B-horizon soils. Sorption data indicated that these PhACs exhibit non-linear sorption relationship in all soils – stronger sorption was observed at lower PhAC concentrations and lower sorption at higher concentrations. Naproxen and ibuprofen sorbed more strongly in A-horizon soils while cetirizine sorbed more strongly in B-horizon soils. Breakthrough curves of these three PhACs measured in homogeneous packed soil columns indicated that PhAC transport was affected by chemical nonequilibrium processes depending on the soil and PhAC chemistry. The shape of the breakthrough curves indicated that there were two distinct sorption sites – OM and clay minerals – which influence nonequilibrium transport of these compounds. While the sorption and transport data do not provide mechanistic information regarding the nature of PhAC interaction with reactive components within geological materials, they do provide important information regarding potential fate of such compounds in the environment. The results also show the role that soil OM and mineral surfaces play in sequestering or transporting these chemicals.