## Facts

- EPA promulgated a Final Test Rule under TSCA § 4 requiring toxicological testing of 2-ethylhexanoic acid (EHA), including animal studies, due to potential adverse health effects.
- The rule also imposed continuing export-notification duties on exporters of EHA.
- EPA concluded existing data were insufficient and relied on inferences about likely human exposure drawn from EHA’s manufacture and industrial uses, rather than requiring direct monitoring evidence of exposure.
- The Chemical Manufacturers Association and four EHA manufacturers petitioned for judicial review seeking to set aside the rule.

## Issues

1. What evidentiary threshold TSCA § 4 requires before EPA may order testing on health-risk grounds—proof of actual unreasonable risk or a non-speculative basis for suspecting such risk.
2. Whether EPA must present direct evidence of actual human exposure, or may infer exposure from the circumstances of manufacture and use.
3. When industry-submitted evidence challenging EPA’s exposure assumptions obligates EPA to rebut that evidence to sustain a test rule.
4. Whether infrequent or one-time exposures can support a TSCA § 4 test rule when potential harms could be serious.

## Decision

- The court denied the petition for review and upheld the Final Test Rule.
- The court sustained EPA’s interpretation that TSCA § 4 permits a test rule when EPA has a “more-than-theoretical” basis for suspecting the chemical may present an unreasonable risk of injury to health.
- The court held EPA may establish the existence and amount of human exposure through reasonable inferences from how the substance is manufactured and used.
- The court held EPA must rebut industry evidence attacking exposure inferences only if that evidence renders EPA’s exposure probability finding no more than theoretical or speculative.
- The court held that infrequent or even one-time exposures can justify a test rule if there is a more-than-theoretical basis to believe exposure at the relevant doses may present an unreasonable risk.

## Legal Principles

- TSCA § 4 authorizes EPA to require testing when there is a non-speculative, more-than-theoretical basis for suspecting a chemical may present an unreasonable risk and existing data are inadequate.
- EPA may rely on inference-based exposure determinations drawn from production and use conditions; direct exposure measurements are not invariably required.
- Industry evidence triggers a duty of rebuttal only when it reduces EPA’s exposure/risk showing to mere speculation; evidence that merely injects uncertainty does not necessarily defeat the rule.
- Low-probability exposure events may support a test rule when potential harms are serious and the risk determination rests on more than speculation.

## Conclusion

The D.C. Circuit upheld EPA’s TSCA § 4 test rule for EHA, approving EPA’s use of inference-based exposure findings and a “more-than-theoretical” risk threshold, and limiting when industry evidence compels EPA to rebut exposure challenges.


Chem. Mfrs. Ass'n v. U.S. Env't Prot. Agency, 859 F.2d 977 (D.C. Cir. 1988)