Iron (hydr)oxide dynamic transformation-induced perfluorooctanoic acid transport and attenuation effect: Impacts of initial goethite and associated minerals content and groundwater type

Abstract

Perfluorooctanoic acid (PFOA) has been widely utilized, leading to serious contamination. Iron (hydr)oxide transformation was varied in media. Whereas, dynamic transformation effect was extensively unclear. Here, iron (hydr)oxide dynamic transformation-induced PFOA transport and attenuation was investigated by emphasizing initial goethite (α-FeOOH) and associated minerals content and groundwater type based on the multi-process attenuation model. Results revealed that groundwater type did not affect the PFOA attenuation pathway. However, it controlled the iron (hydr)oxide dynamic transformation differences. PFOA transport behavior (retardation factor R from 2.61 to 1.91) was significantly affected by iron (hydr)oxide dynamic transformation. Iron (hydr)oxide transformation induced the greatest PFOA transport risk (R = 1.91, attenuation rate λ = 0.0001 min−1) in SO42− environment, where complex α-FeOOH, Fe3O4, and β-Fe2O3·H2O transformed to simplex β-FeOOH, leading to instantaneous (Kd) and kinetic (α) two-site sorption fraction change. Furthermore, the associated mineral Fe3O4 of goethite was crucial in PFOA attenuation (λ from 0.0001 to 0.0002 min−1). Fe3O4 released Fe2+ and the oxidation of Fe2+ to Fe3+ provided electrons, facilitating the formation of F–(CF2)7–COO· radicals, which played a key role in the following cycle attenuation process. This study provides a theoretical basis for understanding the interaction mechanism of PFOA and iron (hydr)oxide dynamic transformation under groundwater differences.