Effect of coexisting Cd(Ⅱ) and As(V) on anionic PFASs sorption in soils: Models and mechanisms

An in-depth understanding of the sorption behaviors of per- and polyfluoroalkyl substances (PFASs) in soil is essential to assess their environmental risks accurately. Due to chemical industry production and waste treatment, co-contamination soil of heavy metals (HMs)-PFASs has become a public concern worldwide. This study investigated soil sorption behaviors of PFASs including perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), and perfluorohexanesulfonic acid (PFHxS). A multiple linear regression (MLR) model was developed to predict the sorption of PFOS in soil. Validation results demonstrated that this model could effectively predict the distribution coefficients (K_d) of PFOS based on soil organic carbon (OC), silt, clay, and free Fe/Al-oxide contents, exhibiting a strong predictive ability (r² = 0.942, p < 0.001). In six soils, HMs (Cd²⁺ and As⁵⁺) influence three anionic PFASs sorption primarily by altering the electrostatic and hydrophobic interactions between soil components and PFASs. The K_d values of PFOS tend to rise with increasing Cd²⁺ concentration but decline with increasing As⁵⁺ concentration. In contrast, HMs have a relatively minor influence on the sorption of PFOA and PFHxS. Moreover, a nonlinear model was constructed for the first time to quantify the impact of HMs on PFASs sorption. The model achieves exceptional prediction accuracy when applied to both experimental data from this study and literature data. A comprehensive understanding of PFASs sorption behavior in soil under conditions of coexisting HMs is of great significance for formulating targeted degradation and mitigation strategies for co-contaminated sites.