Opinion ID: 492025
Heading Depth: 2
Heading Rank: 2

Heading: Promulgation of a Recommended Level of Zero for TCE

Text: 15 Petitioners Halogenated Solvent Industry Alliance and Diamond Shamrock Chemicals Company protest at length the EPA's decision to categorize TCE as a probable carcinogen, which resulted in the agency's promulgation of a recommended level of zero for TCE. Petitioners argue that the EPA miscategorized TCE because any risk presented by the compound is at most de minimis. TCE's carcinogenicity has been the subject of at least six scientific studies on mice, which have produced varying results. Petitioners belittle the two studies that have indicated that TCE may be a human carcinogen, while they trumpet the studies that point the other way. In brief, petitioners argue that the positive studies are unreliable because they involved suspect dosage levels, dosage methods, TCE grades, mice strains, and mice housing. 16 Happily, it is not for the judicial branch to undertake comparative evaluations of conflicting scientific evidence. Our review aims only to discern whether the agency's evaluation was rational. See NRDC v. EPA, 812 F.2d 721, 725 (D.C.Cir.1987). EPA provided ample explanation for its decision to classify TCE as a probable carcinogen. It received and replied to extensive comments on the issue, and it detailed its reasons for giving greater weight to the positive studies than to the negative or inconclusive studies. See 50 Fed.Reg. 46,886-87. To summarize the EPA's reasoning, the agency was particularly impressed by finding in two different studies that TCE caused a significant increase in the incidence of liver tumors in mice. Although we gather there is some disagreement in the scientific community as to the relevance of evidence of mouse tumors, EPA's proposed guidelines for carcinogen risk-assessment reasonably take such findings as sufficient evidence of carcinogenicity in the absence of certain contraindications, none of which was present in the studies in question. Moreover, the agency identified concrete flaws in the negative studies. The agency also took note of the consensus among scientists that where cancer is concerned, positive results in one study are not necessarily negated by negative results in another. EPA, in sum, made a reasonable choice to categorize TCE as a probable carcinogen based on a rational evaluation of somewhat conflicting scientific evidence. As we previously have stated, in an area characterized by scientific and technological uncertainty [w]here administrative judgment plays a key role, ... this court must proceed with particular caution, avoiding all temptation to direct the agency in a choice between rational alternatives. Environmental Defense Fund v. Costle, 578 F.2d 337, 339 (D.C.Cir.1978). We are satisfied that the alternative for which the agency opted was rational, and we therefore have no cause to disturb the EPA's choice. 17