{"id":8524,"date":"2019-02-20T10:04:40","date_gmt":"2019-02-20T15:04:40","guid":{"rendered":"http:\/\/blogs.edf.org\/health\/?p=8524"},"modified":"2021-04-02T14:45:08","modified_gmt":"2021-04-02T19:45:08","slug":"potential-biopersistence-short-chain-pfas","status":"publish","type":"post","link":"https:\/\/blogs.edf.org\/health\/2019\/02\/20\/potential-biopersistence-short-chain-pfas\/","title":{"rendered":"The elephant in the room: potential biopersistence of short-chain PFAS"},"content":{"rendered":"

Maricel Maffini, Ph.D.,<\/em>\u00a0Consultant and Tom Neltner, J.D.<\/em><\/a>,<\/em>\u00a0Chemicals Policy Director<\/p>\n

In January 2018, US Food and Drug Administration (FDA) scientists published a peer-reviewed journal article<\/a> stating a commonly used raw material to make greaseproof paper is likely to persist in the human body. FDA scientists\u2019 sophisticated analysis and remarkable conclusion raises questions about the broad assumption that short-chain perfluorinated alkyl substances (PFAS), as a class, did not accumulate.<\/p>\n

Strangely, two<\/a> recent<\/a> reviews funded by the FluoroCouncil<\/a>, ignored FDA scientists\u2019 study even though it was published ten months before the industry group submitted their analysis for peer-review. The peer reviewers appear to have missed the omission as well. As a result, the industry evaluations continue to perpetuate the flawed assumptions, concluding that perfluorohexanoic acid (PFHxA) and related short-chain PFAS \u201cpresent negligible human health risk\u201d and that this substance alone is a suitable marker for the \u201csafety of fluorotelomer replacement chemistry.\u201d<\/p>\n

In this blog, we discuss the differences between the studies and the implications of the discordance between FDA\u2019s and industry\u2019s conclusions for the safety assessment of short-chain PFAS.<\/p>\n

<\/p>\n

What do we know about short-chain PFAS?<\/strong><\/p>\n

With the phase-out of long-chain PFAS to make water- and grease-proof materials, companies shifted to short-chain fluorotelomer-based chemistry.[1]<\/a> These new raw materials are used to build polymers and include chemicals that contain six fully-fluorinated carbon groups with additional non-fluorinated carbons. These molecules are usually known as C6 and a common starting material for polymers is a 6:2 fluorotelomer alcohol (6:2 FTOH) that has six fully-fluorinated carbons and two non-fluorinated carbons with an alcohol on the non-fluorinated end.<\/p>\n

Industry expected that these C6 compounds, among them 6:2 FTOH and its main manufacturing impurity perfluorohexanoic acid (PFHxA), would: 1) be less toxic than long-chain PFAS such as 8:2 FTOH, PFOA and PFOS; and 2) not accumulate in the body.<\/p>\n

However, these expectations do not hold up under scrutiny. A 2015 study<\/a> by an FDA scientist concluded that \u201csignificant data gaps remain\u201d about the toxicity of the 6:2 FTOH, and in the 2018 study<\/a>, the agency scientists raised the potential for biopersistence.<\/p>\n

Significance of FDA\u2019s conclusion about potential biopersistence of C6 fluorotelomer alcohol<\/strong><\/p>\n

FDA scientists\u2019 thorough evaluation of publicly available[2]<\/a> animal and human exposure data on 6:2 FTOH provided important insight into the body\u2019s transformation of the chemical. They identified three metabolites, namely the PFHxA mentioned above, 5:3 fluorotelomer carboxylic acid (5:3 A) and perfluoroheptanoic acid (PFHpA) that could be used as markers of 6:2 FTOH exposure. For each metabolite, they also provided internal exposure estimates. The figure below shows 6:2 FTOH (in blue box) and how the body converts it to the three metabolites (in red boxes).<\/p>\n

\"\"<\/a><\/p>\n

As a result of their analysis, FDA scientists identified 5:3 A as an important biomarker for the potential biopersistence of 6:2 FTOH <\/strong>because:<\/p>\n