Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are emerging anthropogenic compounds that have recently become the target of global concern due to their ubiquitous presence in the environment, persistence, and bioaccumulative properties. This study was carried out to investigate the migration of PFOS and PFOA in soils and groundwater in a U.S. metropolitan area. We observed elevated levels in surface soils (median: 12.2ng PFOS/g dw and 8.0ng PFOA/g dw), which were much higher than the soil-screening levels for groundwater protection developed in this study. The measured levels in subsurface soils show a general increase with depth, suggesting a downward movement toward the groundwater table and a potential risk of aquifer contamination. Furthermore, concentrations of PFOS and PFOA in monitoring wells in the source zone varied insignificantly over 5 years (2009-2013), suggesting limited or no change in either the source or the magnitude of the source. The analysis also shows that natural processes of dispersion and dilution can significantly attenuate the groundwater contamination; the adsorption on aquifer solids, on the other hand, appears to have limited effects on the transport of PFOS and PFOA in the aquifer. The probabilistic exposure assessment indicates that ingestion of contaminated groundwater constitutes a much more important exposure route than ingestion of contaminated soil. Overall, the results suggest that (i) the transport of PFOS and PFOA is retarded in the vadose zone, but not in the aquifer; (ii) the groundwater contamination of PFOS and PFOA often follows their release to surface soils by years, if not decades; and (iii) the aquifer can be a major source of exposure for communities living near point sources.
Bibliographical noteFunding Information:
This work was supported by a grant (CTS Project #2013003 ) from the Center for Transportation Studies, University of Minnesota . We would like to thank Drs. Brock Matter and Peter Villalta at the Masonic Cancer Center of the University of Minnesota for the use of a liquid chromatograph and a tandem mass spectrometer. We would like to thank Mr. Lanre Adekola and Mr. Aaron Ketchmark from the St. Anthony Falls Laboratory for help with the field collection of samples. The authors thank anonymous reviewers for their constructive comments.
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- Exposure assessment
- Groundwater contamination
- Hot spots
- Natural attenuation
- Soil contamination