Samples from 450 homes with shallow private wells throughout
the
state of Wisconsin (USA) were collected and analyzed for 44 individual
per- and polyfluoroalkyl substances (PFAS), general water quality
parameters, and indicators of human waste as well as agricultural
influence. At least one PFAS was detected in 71% of the study samples,
and 22 of the 44 PFAS analytes were detected in one or more samples.
Levels of PFOA and/or PFOS exceeded the proposed Maximum Contaminant
Levels of 4 ng/L, put forward by the U.S. Environmental Protection
Agency (EPA) in March 2023, in 17 of the 450 samples, with two additional
samples containing PFHxS ≳ 9 ng/L (the EPA-proposed hazard
index reference value). Those samples above the referenced PFAS levels
tend to be associated with developed land and human waste indicators
(artificial sweeteners and pharmaceuticals), which can be released
to groundwater via septic systems. For a few samples with levels of
PFOA, PFOS, and/or PFHxS > 40 ng/L, application of wastes to agricultural
land is a possible source. Overall, the study suggests that human
waste sources, septic systems in particular, are important sources
of perfluoroalkyl acids, especially ones with ≤8 perfluorinated
carbons, in shallow groundwater.