Maximum concentration level for groundwater (MCLgw) and soil control value to protect groundwater (CVSpgw) of hexafluoropropylene oxide trimer acid (HFPO-TA)

As a widely used alternative to the conventional per- and polyfluoroalkyl substances (PFAS) of perfluorooctanoic acid (PFOA), hexafluoropropylene oxide trimer acid (HFPO-TA) is of growing concern due to its toxicity and potential risks to human health. Water quality criteria of HFPO-TA for protecting human health were established, and 412 ng/L was set as the maximum concentration level for groundwater ( MCL gw ) to calculate the soil control value to protect groundwater ( CVS pgw ). Utilizing recommended default values for the properties of HFPO-TA and the soil, the generic CVS pgw value of 24.0 μg/kg was obtained. Subsequently, column experiments were conducted to investigate the transport of HFPO-TA in the site soil of a fluorochemical industrial park (FIP) in China. The resulted retardation factor ( R ) was applied to derive the site-specific CVS pgw , and a value of 2.48 μg/kg was obtained. Using the experimentally measured R instead of the default empirical values reduced the uncertainties in deriving the CVS pgw dramatically. The transport of 13 PFAS in the soil as a mixture was investigated and revealing a significant linear correlation between R and organic carbon-water partition coefficient ( K OC ) ( r 2  = 0.991, p  < 0.01), which was utilized to predicted R values for PFAS compounds. Comparison to the site-specific CVS pgw , HFPO-TA in the soil near the FIP may pose a risk to the groundwater quality. HFPO-TA concentrations in the groundwater of certain areas around the FIP were higher than MCL gw and not recommended for directly consumption, while HFPO-TA in the tap water was at the safe level.