ELR Citation: ELR 21210
No(s). 93-1178 (D.C. Cir. Jul 19, 1994)

The court vacates the U.S. Environmental Protection Agency's (EPA's) decision to list methylene diphenyl diisocyanate (MDI) as a high-risk air pollutant for purposes of the Clean Air Act's early reduction program. Under the program, a participating facility may use emission reductions for one pollutant that exceed required reductions to offset certain emissions of another pollutant. Facilities may not use such offsetting reductions against emissions of pollutants that EPA designates as high risk. EPA listed hazardous air pollutants (HAPs) as high risk if it determined that they may be toxic at or below certain threshold ambient concentrations. As a measure of a pollutant's toxicity, EPA used an inhalation reference concentration (RfC) extrapolated from animal studies. Generally, EPA considered for inclusion on the high-risk list only those HAPs for which it had an RfC in its Integrated Risk Information System (IRIS) database. To determine the likely level of human exposure to a HAP, the Agency developed a generic air dispersion model. EPA proposed to limit high-risk designation to pollutants for which actual emissions exceed 10 tons per year from at least one reporting facility, but it decided not to include this criterion in the final rule.

The court first holds that EPA complied with notice-and-comment requirements for developing its MDI air dispersion model. EPA set out the basis for the model in the notice of proposed rulemaking for the rule containing its high-risk listing standards. It stated its rationale for making various assumptions, and it requested comments on the assumptions it made. Also, it addressed significant comments in the background paper referred to in its final rule document, and it revised some modeling parameters based on the comments it received. The court next holds that EPA was not required to subject its IRIS database to public comment. The database has no preclusive effect, and the application of the data was clearly part of the proposed rule. As such, it was the subject of notice and comment. The court notes that petitioner has not demonstrated that EPA ignored its comments with respect to the RfC for MDI.

Turning to petitioner's substantive claims, the court holds that EPA's generic air dispersion model does not bear a rational relationship to the physical properties of MDI. The model rests on the assumptions that the pollutant will be a gas emitted at 20 degrees centigrade from a single 10-meter stack and that it will disperse as a gas through the atmosphere under certain specified meteorologic conditions. Petitioner presented evidence, uncontested by EPA, that MDI is a solid at 20 degrees centigrade, that it tends not to evaporate, and that it typically disperses as an aerosol. EPA has not pointed to any evidence that shows a rational relationship between the model and MDI's physical properties. Also, when it eliminated the proposed 10-ton criterion for listing high-risk pollutants, it did not substitute any other mechanism for validating the predicted level of human exposure by reference to actual emissions.

The court holds that EPA acted arbitrarily and capriciously by listing MDI as a high-risk pollutant solely based on MDI's RfC without identifying any serious health effect with which it has ever been associated. EPA asserts that nasal irritation resulting from excessive exposure to MDI is the type of serious health effect associated with a "high risk" HAP. In the preamble to its final high-risk listing rule, EPA stated that it would consider for the high-risk list only pollutants associated with a serious health effect. EPA failed, however, to screen out nonserious health effects. In determining that MDI is relatively toxic, EPA relied solely on the presence in the IRIS database of an Agency-verified RfC for MDI, without regard to the seriousness of the health effect associated with that RfC. Nasal irritation is not a health effect included in EPA's list of serious health effect endpoints: Carcinogenicity, reproductive and developmental toxicity, acute lethality, and other systemic disorders.

The court vacates EPA's decision to list MDI as a high-risk air pollutant, but does not remand the decision for further administrative proceedings. EPA did not suggest in its rulemaking that there is any alternative basis in the record for including MDI on the high-risk list. Finally, the court denies petitioner's request to extend the statutory period for a manufacturer to enroll in the early reduction program and thereby to seek an extension of the deadline for complying with the Clean Air Act's maximum achievable control technology (MACT) requirements. EPA has not yet promulgated MACT standards for most industries that emit MDI, and therefore the enrollment period for a compliance extension has not closed for those industries.

Counsel for Petitioner
David J. Hayes
Latham & Watkins
1001 Pennsylvania Ave. NW, Ste. 1300, Washington DC 20004
(202) 637-2200

Counsel for Respondents
Scott A. Schachter
Environment and Natural Resources Division
U.S. Department of Justice, Washington DC 20530
(202) 514-2000

Before SILBERMAN, WILLIAMS, and GINSBURG, Circuit Judges.