On June 27, 2019, the Michigan Science Advisory Workgroup (the Workgroup) issued its Health-Based Drinking Water Value Recommendations for PFAS in Michigan. In late March 2019, Gov. Gretchen Whitmer announced the formation of the Workgroup and her order was for the Michigan Department of Environment, Great Lakes, and Energy (EGLE), formally the Michigan Department of Environmental Quality, to initiate rulemaking to establish enforceable limits for the presence of per- and polyfluoroalkyl substances (PFAS) in Michigan's drinking water. PFAS are a category of man-made chemicals that have been widely used to make products because of their stain-resistant, waterproof and/or nonstick properties and are also in fire-fighting foam. Under Governor Whitmer's order, the Workgroup was directed to issue its recommended health-based values by July 1, 2019.

The Workgroup utilized existing and proposed standards from across the country for the 18 PFAS analytes considered under the United States Environmental Protection Agency's Method 537.1. The Workgroup's analysis was focused on those PFAS that, from its perspective, had a sufficient number of peer-reviewed studies on which to base its conclusions. Based on this analysis, the Workgroup selected PFOA, PFOS, PFHxS, PFHxA, PFBS, PFNA and GenX as PFAS analytes for which the Workgroup would then develop individual public health toxicity values. The remaining PFAS values within Method 537.1 were later considered as to whether a class-based or group-based public health toxicity value could be applied.

For each of the selected PFAS analytes, the Workgroup identified points of departure (defined as the point on a toxicological dose-response curve corresponding to an estimated low effect level or no effect level) and the critical studies that served as the basis of public health toxicity values. The Workgroup then identified appropriate uncertainty factors to derive public health toxicity values. According to the Workgroup, it then “recommended specific drinking water exposure paradigms, accounting for sensitive sub-populations, and applied selected relative source contribution factors to derive drinking water health-based values.”1

Finally, the Workgroup considered the PFAS analytes from Method 537.1 that were not selected for the development of individual criteria to determine whether a class-based or grouping-based evaluation approach would be appropriate. The Workgroup concluded that a screening level approach was valid to assess longer-chain PFAS based on the lowest derived drinking water health-based values.

Based on its review, the Workgroup has recommended the following health-based drinking water values (HBVs):

Summary Table of Drinking Water HBVs

Specific PFAS

Drinking Water Health-based Value

Chemical Abstract Services Registry Number (CASRN)

PFNA

6 ng/L (ppt)

375-95-1

PFOA

8 ng/L (ppt)

335-67-1

PFHxA

400,000 ng/L (ppt)

307-24-4

PFOS

16 ng/L (ppt)

1763-23-1

PFHxS

51 ng/L (ppt)

355-46-4

PFBS

420 ng/L (ppt)

375-73-5

GenX

370 ng/L (ppt)

13252-13-6

For all other PFAS on the Method 537.1 analyte list,2 the Workgroup recommendation is to use the lowest long-chain (eight carbons and above for carboxylates and six carbons and above for sulfonates) HBV of 6 ppt, which is the HBV for PFNA, because the similarity in toxicity for the long-chain PFAS is expected to produce similar health effects.

In addition to its HBV recommendations, the Workgroup recommended additional monitoring, research for potential sources, notification of the public, and efforts to reduce exposure. It noted that the scientific evidence on PFAS is expanding rapidly and that the guidelines may need to be revised periodically. The Workgroup further noted that there remains significant scientific uncertainty, and additional research on PFAS exposure is warranted.

Having now received the Workgroup's recommendations, the Michigan Department of Environment, Great Lakes, and Energy will continue its rulemaking process to establish enforceable Maximum Contaminant Levels for PFAS in Michigan's drinking water supplies. Under the Governor's order, the proposed regulations will be drafted and put out for comment by October 1, 2019. The final rule is expected to be adopted by April 2020.