Fate of a perfluoroalkyl acid mixture in an agricultural soil studied in lysimeters.

Abstract Perfluoroalkyl acids (PFAAs) are environmental contaminants of concern in both food and drinking water. PFAA fate in agricultural soil is an important determinant of PFAA contamination of groundwater and crops. The fate of C4-C14 perfluorinated carboxylic acids (PFCAs) and two perfluorinated sulfonic acids (PFSAs) in an agricultural soil was studied in a field lysimeter experiment. Soil was spiked with PFAAs at four different levels and crops were planted. PFAA concentrations in soil were measured at the beginning and end of the growing season. Lysimeter drainage water was collected and analysed. The concentrations of all PFAAs decreased in the surface soil during the growing season, with the decrease being negatively correlated with the number of fluorinated carbons in the PFAA molecule. PFAA transfer to the drainage water was also negatively correlated with the number of fluorinated carbons. For the C11-C14 PFCAs most of the decrease in soil concentration was attributed to the formation of non-extractable residues. For the remaining PFAAs leaching was the dominant removal process. Leaching was concentration dependent, with more rapid removal from the soils spiked with higher PFAA levels. Model simulations based on measured K d values under-predicted removal by leaching. This was attributed to mixture effects that reduced PFAA sorption to soil. Highlights • K d for C4-C14 PFCAs increased by 0.39–0.48 log units per perfluorinated carbon atom. • C4-C7 PFAAs were almost completely removed from the 60 cm deep lysimeter after 72 days. • Leaching (%) increased with the initial concentration of the PFAA mixture in the soil. • Modeling using measured K d values underestimated observed loss of PFAAs from soil. • Accelerated leaching was attributed to competition with other PFAS for sorption sites. [ABSTRACT FROM AUTHOR]