## Facts

- EPA promulgated a rule under the Safe Drinking Water Act (SDWA) setting a recommended maximum contaminant level (RMCL) for fluoride in public drinking water systems at 4 mg/L.
- EPA based the RMCL on a scientific record focused on preventing serious health effects, including crippling skeletal fluorosis.
- NRDC petitioned for review, arguing 4 mg/L inadequately protected high-volume water drinkers from crippling skeletal fluorosis and that EPA understated certain fluoride-related risks.
- NRDC also challenged EPA’s classification of dental fluorosis as a cosmetic effect relevant to secondary standards rather than an “adverse health effect” triggering primary standards.
- South Carolina’s environmental agency also petitioned for review, arguing the evidence was too uncertain to justify an RMCL or supported a higher RMCL than 4 mg/L.
- The petitions were consolidated for direct appellate review of EPA’s final rule on the administrative record.

## Issues

1. Whether EPA acted within its SDWA authority and discretion in setting the fluoride RMCL at 4 mg/L in light of evidence on skeletal fluorosis and exposure risks.
2. Whether EPA reasonably interpreted “adverse health effect” under the SDWA to exclude dental fluorosis as primarily cosmetic, allowing regulation through secondary rather than primary standards.
3. Whether scientific uncertainty required EPA to set no RMCL or a higher RMCL, as argued by South Carolina.

## Decision

- The D.C. Circuit denied both petitions for review and upheld EPA’s fluoride RMCL rule in full.
- The court held EPA reasonably interpreted the SDWA, evaluated conflicting scientific evidence, explained its determinations, and adequately answered petitioners’ objections.
- The court accepted EPA’s critique of NRDC’s risk calculations as methodologically unreliable (including overestimating exposure based on an inapt water-consumption assumption).
- The court upheld EPA’s judgment that dental fluorosis could be treated as a cosmetic/public-welfare concern rather than an adverse health effect requiring primary regulation.
- The court rejected the argument that uncertainty compelled inaction or a higher RMCL, finding EPA could make a reasoned judgment on an imperfect record.

## Legal Principles

- Under arbitrary-and-capricious review, a court will sustain an SDWA standard where the agency reasonably interprets the statute, evaluates disputed scientific evidence, and provides a rational explanation grounded in the record.
- Courts generally defer to EPA’s expert risk-assessment choices when the agency addresses material criticisms and explains why competing analyses are less reliable.
- The SDWA permits EPA to distinguish between “adverse health effects” supporting primary standards and cosmetic/public-welfare effects supporting secondary standards, so long as the interpretation is reasonable.
- Scientific uncertainty does not bar regulation; the SDWA contemplates agency judgment based on available evidence rather than requiring conclusive proof before acting.

## Conclusion

The D.C. Circuit upheld EPA’s 4 mg/L fluoride RMCL as a permissible exercise of discretion under the SDWA, deferring to EPA’s scientific judgments and statutory interpretation, including its treatment of dental fluorosis as a cosmetic effect addressed through secondary standards.


Nat. Res. Def. Council, Inc. v. EPA, 812 F.2d 721 (D.C. Cir. 1987)