A particle interaction model of reversible organic chemical sorption

Abstract

Understanding the factors governing irreversible and reversible sorption is essential to predict the influence of sediment on contaminant fate and transport in surface waters. This study used sediment of an urban water body to demonstrate irreversible accumulation and reversible absorption of perfluoroalkyl acids (perfluorooctane sulfonate (PFOS), perfluorononanoic (PFNA) and perfluorodecanoic acid (PFDA)) during two sorption–desorption (S–D) cycles. Absorption and desorption isotherms were consistent with sorption to irreversibly absorbing glassy sediment organic carbon (SOC) and liquid–liquid like partitioning to rubbery SOC. The observed absorption isotherms and the desorption isotherms were adequately fitted linear models. Irreversible absorption showed signs of saturation and the reversible partitioning diminished during the 2nd S–D cycle causing the composite sorption capacity to decrease. Results suggest that under the conditions tested, surface water sediment can act as sink for the studied PFAAs. Rubbery SOC can potentially release or absorb contaminants, thus acting as a concentration buffer. S–D cycling can cause irreversible absorption concentration to increase even when exposure occurs at lower concentrations (i.e. 5μg/L). logKOC values of sediment that underwent S–D cycling overlaps with the range of field date, suggesting that the sediment of surface water may have experienced some degree of S–D cycling.