Perfluoroalkyl substances in the groundwater of Stockholm, the role of subsurface reactions.

Abstract: Perfluoroalkyl acids (PFASs) are toxic pollutants ubiquitously found in the ecosystem. Recent investigations have focused on describing their environmental behavior and spreading. This includes transportation by water, where groundwater can continue to spread the contaminants a long time after the use has ended. This thesis surveys the existing literature on the reactions in soil that decides the presence and composition of PFASs in groundwater. A chemical groundwater investigation was recently done by Stockholm’s Environmental and Health Administration. The thesis presents a quantitative analysis of the PFASs’ content in Stockholm’s groundwater to verify if it conforms to the literature. A statistical analysis of the ratio between perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) is included to test if the PFAS composition in groundwater is influenced by soil reactions. The literature states that due to the high water solubility, low volatility and moderate adsorption, PFASs are likely to be encountered in groundwater. The adsorption depends on both PFASs’ and soil’s properties. The quantitative analysis confirms the influence of the PFASs’ properties in Stockholm’s groundwater, where both more short-chained PFASs and carboxylates are present. However, the analysis could not confirm the influence of the soil properties in adsorption at normal environmental conditions. The statistical analysis shows that the ratio of PFOS to PFOA is increased in groundwater in comparison to stormwater (p < 0.15). The increase cannot be explained by the hypothesis that the adsorption of PFAS governs this behavior, since PFOS is a sulfonate and longer than PFOA. An explanation is found in the degradation of precursors, which seems to contribute to PFOS concentrations in groundwater. This shows the important contribution of degradation of precursors to PFOS concentrations and motivates further investigations on the matter.