At the time the CT Action Levels for PFOA, PFOS, PFHxS, and PFNA were developed, there were insufficient toxicity data to allow DPH to include other PFAS chemicals. The PFAS analytical methods currently used for drinking water analyzes for a total of 29 PFAS chemicals out of the thousands of PFAS that are currently known to exist. Of these 29 chemicals, recent testing in CT shows that PFBS and PFHxA are the most commonly detected PFAS that are not part of the current four individually developed Action Levels. To date, no federal agency has set a safe drinking water level for either PFBS or PFHxA. CT DPH monitors the evolving toxicity data for these and other PFAS chemicals to identify when new or updated Action Levels are needed.
There is another consideration for why PFAS chemicals like PFBS and PFHxA are not part of the current PFAS Action Level. PFBS and PFHxA are compounds with short-chain chemical structures and thus are very different from the four PFAS with Action Levels, which have long-chains. We know from studies of humans and laboratory animals that short-chain PFAS are eliminated from the body much more quickly (on the order of days to months in humans) than long-chain PFAS (on the order of years in humans). Because short-chain PFAS are removed so quickly from the body, they are less likely to build up in the blood to a level that could cause toxicity. This is supported by the limited toxicity data (mostly from laboratory animal studies) for PFBS and PFHxA that indicate these chemicals appear to be much less toxic than long-chain PFAS such as PFOA and PFOS.