Opinion ID: 744479
Heading Depth: 3
Heading Rank: 4

Heading: ipbc

Text: 75 IPBC is a white, crystalline solid used in products to prevent the growth of mildew and fungi. The EPA listed IPBC as a chronic toxicant based on two animal studies. A 90-day study observed increased liver-to-body-weight ratios in rats following exposure to IPBC. A two-year study revealed non-neoplastic pathological changes in the rats' stomachs. Troy argues that the EPA failed to review the studies seriously or to indicate why stomach irritation in rats would suggest a potential hazard to humans given differences in the species' anatomies. Troy also argues that the EPA violated its own Guidelines which, Troy argues, require the EPA to present evidence of chronic toxicity in two or more species of animals. 76 Although the agency's presentation of the evidence might have been more detailed, the EPA has described its methodology and the results of the studies and has adequately justified the basis for its scientific conclusions. Nor can we credit appellants' argument that differences in the anatomies of rats and humans invalidate these conclusions. Although it is true that humans do not have an organ equivalent to the rat's forestomach, the EPA has explained that the rat's forestomach contains a tissue known as squamous epithelium and this tissue is also found in the human esophagus, pharynx, larynx, oral cavity, and ano-rectal junction. We hold that the EPA has presented sufficient evidence to list IPBC. 77 Moreover, the EPA has done all that the Guidelines required of it with regard to IPBC. The Guidelines state that 78 chemicals with adequate evidence of chronic toxicity in humans and/or two species of animals are considered sufficient for listing and may be added to the section 313 list following study validation, whereas chemicals with suggestive evidence of toxicity in humans or animals may be sufficient for listing and are evaluated on a case-by-case basis for addition to the list. 79 Guidelines at 29. Although the categories sufficient for listing and may be sufficient for listing appear to conflate the toxicity screen with the final listing decision, as we noted above, this categorization served only to exclude chemicals found to be insufficient for listing. The Guidelines require, and EPA conducted, further proceedings with regard to any chemicals not excluded at this first step. This further review satisfied the case-by-case evaluation required for chemicals, such as IPBC, with only suggestive evidence of toxicity based on one species of animal. We, therefore, conclude that the agency did not act contrary to its Guidelines in listing IPBC.