Evaluation of PFAS in Environmental Solids: Retention Devices and a Screening Method
Per- and polyfluoroalkyl substances (PFAS) present a threat to global ecosystems and human health due to their ubiquitous use and unique physicochemical properties. Through direct and indirect emissions, PFAS can end up in soil which serves as both a reservoir and a source of further contamination. Thus, there is a need to find ways to limit PFAS spread and quickly identify contaminated sites.To address this first need, environmental and bench-scale tests were conducted to investigate PFAS sorption to sediment retention devices and to evaluate their potential to limit PFAS spread. Devices such as straw wattle and SiltSoxx are commonly used to filter stormwater and may already be environmentally exposed to PFAS. Urban fires like the 2018 Camp Fire in Paradise, CA, are potential sources of PFAS contamination as PFAS-containing household objects burn and release PFAS; sediment retention devices deployed after these disasters are likely exposed to PFAS in stormwater runoff. To determine if PFAS sorption occurs on these devices, samples of SiltSoxx and straw wattle deployed after the Camp Fire were analyzed with combustion ion chromatography for total fluorine (TF) and extracted organic fluorine (EOF). While no correlation between TF and EOF was found, EOF concentrations of both SiltSoxx and straw wattle were higher than typical background concentrations found by others, indicating that PFAS sorption is likely to have occurred. Kinetics tests were used to establish the sorption equilibrium time and partition coefficients were calculated to compare sorption capacity for each material across a range of spiked DOC and PFOA concentrations. DOC was found to facilitate fluorine sorption to both materials. SiltSoxx in the presence of high and low DOC had higher partition coefficients than straw wattle. SiltSoxx also had higher average sorbed concentrations than straw wattle. It was thus concluded that SiltSoxx is the better choice for deployment and limiting PFAS spread after urban fires. In addition to limiting PFAS spread, there is also a need to identify contaminated sites. Current analytical methods, due to tradeoffs between inclusivity and selectivity and limitations from sample characteristics, are an obstacle to easy identification of contaminated sites. Agencies that send out samples to analytical laboratories using these methods are further subject to long delays and high costs. To facilitate identification of contaminated sites, a screening method involving optimized extraction, combustion, and Fourier Transform Infrared (FTIR) analysis was developed. As PFAS combustion breakdown products form SiF4, FTIR analysis provides a novel way to assess PFAS concentration from SiF4 maximum peak area. Calibration curves relating concentrations of GenX, PFOA, and PFOS to SiF4 maximum peak area were created, and method detection limits and limits of quantitation were determined. The final method detection limits - 13.82, 13.18, and 15.31 µg F/g for GenX, PFOA, and PFOS respectively - are environmentally relevant since contaminated sites regularly have concentrations that exceed these limits. Therefore, this screening method is applicable to environmental testing and can be used to quickly identify samples that are contaminated and in need of further analysis.
PFAS, Screening method, Sediment retention devices, Stormwater, Urban fire
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