Comprehensive adsorption behavior and mechanism of PFOA and PFCs in various subsurface systems in China

Abstract

The adsorption-desorption performance of perfluorooctanoic acid (PFOA), one of the environmentally persistent pollutants which is refractory to degrade in soil, was investigated and reported. The adsorption-desorption process of PFOA was firstly conducted using different fractions (sand, coarse silt and fine silt) of soil collected from Shanghai, China. More than 50% of PFOA (2.0 mg/L) could be adsorbed by soils while only less than 10% of which could be desorbed once contamination occurs. The kinetics and particle diffusion rates of PFOA in different fractions of soil were calculated and analyzed in detail. Apart from this, the retention of short-chained PFCs, which can be generated as degradation products of PFOA, were also measured. In single solute systems, the adsorption of pollutants in soils dramatically increased as the chain length of PFCs grew longer. Similarly, in mixed solutions, preferential adsorption of longer-chained PFCs over shorter chains in soils were sited, attributable to the stronger hydrophobicity of the pollutants. However, the desorption of them performed in reverse, where the desorption rates of longer-chained PFCs were far lower than those of shorter ones. Furthermore, influencing factors including pH, temperature and co-existing matters were studied during the adsorption process. After comprehending the adsorption behavior of PFOA in soil fractions, the situation of the adsorption of PFOA in various soils chosen from nine provinces in China was investigated and compared. There was an obvious discrepancy, whether it be from the rate or the amount of adsorption of PFOA (approximately 10%), in the nine different soils. Finally, a multiple linear regressive equation was employed to sort influencing parameters which are prone to affect the adsorption of PFOA in soils, the contribution of these are provided in order of relevance. These results demonstrate the adsorption performance and behavior of PFOA and PFCs in different soils, which can be utilized as a scientific reference for maximizing remediation of PFOA polluted sites in the future.