Regulatory Framework

EPA used a factor called the Relative Source Contribution (RSC) in calculating the lifetime health advisory levels for PFOS and PFOA to account for non-water exposures. From a national perspective, the dominant source of human exposure to PFOS and PFOA is expected to be from the diet (food and water); indoor dust from carpets and other sources is also an important source of exposure, especially for children. The HA was calculated using a RSC of 20%, which allows for other PFOS and PFOA exposure sources (e.g., dust, diet, air) to make up 80% of the dose of exposures (RfD).

More information on the EPA method for calculating a health advisory level is available from the EPA Document EPA-822-B-00-004, Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health 2000, October 2000 and the EPA’s Webpage for Drinking Water Health Advisory for PFOS and PFOA (

Regulatory Framework Q&A’s can be found here DACM Corner Newsletter-FINAL-January 2016.pdf