Effect of repeated sorption-desorption on irreversible and reversible absorption of hydrophobic perfluoroalkyl acids to freshwater sediment

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. 5 mu g/L). log KOC 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.(C) 2022 The Author(s). Published by Elsevier B.V.

Automated summary

Understanding irreversible and reversible sorption in sediment is crucial for predicting the fate and transport of contaminants in surface waters. This study demonstrated the irreversible accumulation and reversible absorption of perfluoroalkyl acids in sediment from an urban water body. The results suggest that sediment can act as a sink for the studied contaminants and rubbery SOC may act as a concentration buffer. The S-D cycling can increase the irreversible absorption concentration, even at lower exposure concentrations, and the log KOC values of the sediment overlap with field data.