## Facts

- EPA issued “low-lead” gasoline regulations requiring stepwise annual reductions in the lead content of leaded gasoline.
- EPA acted under Clean Air Act § 211(c)(1)(A), authorizing regulation of fuels or additives whose emissions “will endanger the public health or welfare.”
- Lead-additive manufacturers and related industry groups petitioned for review, arguing the record did not justify regulation.
- A prior D.C. Circuit panel vacated the rules as arbitrary and capricious, interpreting § 211(c)(1)(A) to require a factually supported showing that automotive lead emissions measurably increase human lead burden and cause significant health hazards to a substantial portion of the public.
- The D.C. Circuit granted rehearing en banc, vacated the panel decision, and reconsidered the statute’s evidentiary demands and the scope of judicial review.

## Issues

1. Whether Clean Air Act § 211(c)(1)(A)’s “will endanger” standard permits EPA to regulate based on significant risk, or instead requires proof of actual, quantified harm to a substantial portion of the population.
2. Whether EPA’s lead-reduction regulations were “arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law” under APA § 706(2)(A).
3. Whether EPA may evaluate endangerment by considering cumulative lead exposure from multiple sources rather than isolating the effects of gasoline lead “in and of itself.”

## Decision

- The en banc court denied the petitions for review and upheld EPA’s lead-reduction regulations.
- The court held that § 211(c)(1)(A) is precautionary and authorizes regulation when EPA finds a significant risk of harm, even if science does not permit definitive proof or full quantification.
- The court concluded EPA rationally found that lead emissions from gasoline present a significant risk of harm to urban populations, especially children.
- Applying APA § 706(2)(A), the court held the agency’s action was not arbitrary or capricious and that judicial review could not replace EPA’s policy and scientific judgments with the court’s own.
- The court approved EPA’s consideration of cumulative lead exposure and rejected a requirement that EPA isolate gasoline lead from other lead sources.

## Legal Principles

- When a statute authorizes regulation upon a finding that emissions “will endanger” public health or welfare, an agency may act on a reasoned assessment of significant risk; it need not wait for conclusive proof of realized harm.
- An agency’s reasonable interpretation of an ambiguous statutory endangerment standard is entitled to substantial deference.
- Under APA arbitrary-and-capricious review, courts examine whether the agency considered relevant factors and articulated a rational connection between the record and its choice, but may not substitute their judgment for the agency’s in technically complex matters.
- In assessing endangerment, an agency may account for cumulative exposure and aggregate risk when the public health concern depends on total body burden from multiple sources.

## Conclusion

The en banc D.C. Circuit sustained EPA’s phased reduction of lead in gasoline, holding that the Clean Air Act’s “will endanger” language permits precautionary regulation grounded in a reasoned finding of significant risk and that EPA’s action survived arbitrary-and-capricious review despite scientific uncertainty.


Ethyl Corp. v. EPA, 541 F.2d 1 (D.C. Cir. 1976) (en banc)