Effect of corn straw biochar application to sediments on the adsorption of 17α-ethinyl estradiol and perfluorooctane sulfonate at sediment-water interface

Abstract The immobilization of organic contaminants in sediment-water systems is of growing concern. Using biochar as sorbent amendment to reduce the mobility of pollutants in the sediment-water interface is becoming increasingly popular as a low-cost and environmentally friendly option. In this study, we mixed sediment from the Weishan Lake with biochar (0%, 2%, and 5% (w/w)) derived from corn straw to investigate the adsorption of perfluorooctane sulfonate (PFOS) and 17α-ethinyl estradiol (EE2). Biochar addition significantly improved the adsorption rates and capacities of EE2 and PFOS on sediments by the factors 1.7–3.5; the organic carbon concentration in the sediment was the main factor influencing this process. The sorption of EE2 and PFOS to sediment was near-linear (Freundlich exponent 1/n of 0.799–0.805), but non-linear for biochar (0.430–0.476) and sediment+biochar (0.370–0.421). The mobility of PFOS in the water-sediment system after biochar addition was significantly reduced, with a considerable increase (about three times) in the sediment-water distribution coefficient K d . Compared to EE2, PFOS is anionic compound and contains hydrophobic C–F chains and hydrophilic S–O groups, making it more susceptible pH influences and resulting in interactions with–OH, –C=O, Si–O–Si, –O–Si, and –Al–O–Al groups via hydrogen bonding, ligand exchange, and surface complexation. We suggest that biochar amendment at ～5% is a viable approach to immobilize EE2 and PFOS at the sediment-water interface.