Lessons Learned from EPA’s Health Risk Assessment of TCE

Lisa Binder and Maria Hoye

The U.S. Environmental Protection Agency (EPA) has issued draft changes to its risk values for trichloroethylene (TCE). The proposal significantly increases the risk indicated by the values associated with TCE (see J. Peters and M. Murphy, “Changing Cleanup Standards for TCE and 1,1-DCE,” Superfund and Hazardous Waste Committee Newsletter, ABA Section of Environment, Energy, and Resources, Vol. 4, No. 2 (Mar. 2003)). Before determining final values, EPA must first resolve questions raised by experts reviewing the draft. To this end, EPA intends to schedule additional stakeholder meetings on the values. Yet even now, EPA regions have already begun to use the draft values on a provisional basis to establish cleanup levels for sites around the country. As described below, the proposed TCE values and their provisional implementation are instructive for the regulated community and underscore the importance of taking an active and early role in the health risk assessment process.

Background
On Sept. 19, 2001, EPA released its draft health risk reassessment for TCE (the “Draft HRA”) (see 66 Fed. Reg. 48257 (Sept. 19, 2001)). The Draft HRA concluded that TCE poses a higher health risk than previously thought for susceptible populations such as children, people with chronic disease and people with higher background exposures. The Draft HRA presented a summary of data that had become available since the earlier TCE assessment and proposed new cancer slope factor (CSF), oral reference dose and inhalation reference dose values for TCE. These draft values are significantly changed from the previous values in use for TCE, indicating a much higher health risk. For instance, the upper range of the draft CSF is approximately 20 times higher than the values currently in use (Murphy and Peters, above).

Following issuance of the Draft HRA, EPA forwarded the document to the Scientific Advisory Board (SAB) for technical review. The SAB was established by Congress in 1978 and has a broad mandate to advise EPA on technical matters, including the quality and relevance of scientific information relied on by EPA as the basis for enacting regulations or policies. The SAB issued a written evaluation of the Draft HRA in December 2002 (EPA Draft Trichloroethylene Health Risk Assessment: Synthesis and Characterization: An EPA Science Advisory Board Report Review of Draft, Dec. 2002, #PA-SAB-EHC-03-002, available at http://www.epa.gov/sab/pdf/ehc03002.pdf). In its report, the SAB noted that the Draft HRA is a “good starting point for completing the risk assessment of TCE.” However, the SAB went on to state that, “there is a need to strengthen the rigor of the discussion in the revised assessment so that the basis for all derived values is transparent and clearly supported by the available data” and “public comments have raised valid concerns the Agency should carefully address.” The SAB called for more information regarding a variety of issues, including the cancer risk associated with TCE exposure, whether TCE affects children and adults differently, the appropriate background exposures for TCE and additional risk factors associated with TCE. The SAB also specifically directed EPA to provide a more quantitative analysis regarding the new values and to evaluate all available studies in the literature.

Status of the Draft Values
EPA had previously suggested that its final health risk reassessment for TCE would be issued sometime in the fall of 2003. However, it may take EPA longer than originally expected to complete the final assessment. According to the Press Office at the EPA National Center for Environmental Assessment, EPA is currently planning an outreach effort to engage stakeholders and the scientific community in discussions regarding the proposed TCE values. Scheduling these meetings could take several months; EPA will publish a notice in the Federal Register to inform the regulated community of the stakeholder meetings. Following these meetings, EPA anticipates that it will make necessary revisions to the Draft HRA to address concerns raised by the SAB and the stakeholders. Once the values are reissued in final form, the values and supporting information will be added to EPA’s Integrated Risk Information Service (IRIS) database.

Regional Reliance on the Draft Values
Although the Draft HRA states on its face that it “should not at this stage be construed to represent Agency policy,” the NCEA Superfund Technical Support Group has adopted the draft values as “provisional” values for use in site screening and cleanups. Based on the NCEA adoption of these provisional values, several EPA regions have already used the values to revise screening levels for contaminated sites.

In October 2002, for instance, EPA Region 9 established new Preliminary Remediation Goals (PRGs) for TCE. PRGs are generic risk-based screening levels used early in the investigation process to eliminate those sites which clearly pose no significant health risk. The new PRGs are based on the high end of the proposed CSF and are significantly lower than the previous PRGs for TCE. For example, the old residential soil PRG was 2.8 mg/kg, and the new PRG is 0.053 mg/kg, more than a fifty-fold decrease. EPA Region 3 has also incorporated the draft values into its own table of risk-based concentration levels.

In addition, EPA Region 9 has imposed new monitoring requirements at remediation sites, at least in part due to the increased draft risk values for TCE. For instance, Region 9 has recently required indoor and outdoor air monitoring at certain Superfund sites in northern California in order to assess potential health impacts from TCE vapors migrating through the soil and into buildings at the sites. It is likely that EPA will require such monitoring at other sites in California and elsewhere as it works to evaluate and address the risks associated with TCE exposure.

Lessons Learned
The ramifications of the new TCE values will be significant. They could affect site screening and remediation for contaminated sites throughout the country. Once final, they may also affect the status of TCE under other federal and state regulatory schemes. Although the public comment period on the Draft HRA has long been closed, EPA will schedule stakeholder meetings within the next few months to discuss the Draft HRA, and it is essential that stakeholders participate in these meetings to voice their concerns. It is not certain, however, that the draft values will change, and EPA regions have already implemented the values on a provisional basis and imposed new requirements at Superfund sites as a result. Even as stakeholders work with EPA over the coming months on the toxicological issues raised by the Draft HRA, they should carefully evaluate how the provisional application of the new TCE values might affect their ongoing site characterization and remediation efforts.

The TCE reassessment highlights the importance of participating in the health risk assessment process. EPA likely will reassess other compounds of concern within the next few years, including other widely used solvents such as tetrachloroethylene (PCE). As the history of the Draft HRA demonstrates, the regulated community should play an active role in risk assessments for such compounds. In order to maximize their input into the process, stakeholders should track EPA’s risk assessment projects carefully and submit timely and comprehensive comments on draft reassessments for compounds of concern. It may also be possible and desirable to meet with EPA staff prior to issuance of the draft assessment to present relevant scientific data. If EPA submits the assessment to the SAB technical review process, that is also an important proceeding and is one in which stakeholders should participate by nominating review panel members, submitting comments, and monitoring the SAB outcome and EPA’s response to it. And because draft values might be applied on a provisional basis, stakeholders should evaluate how the provisional application of new values could affect their site activities.

Ms. Binder and Ms. Hoye are attorneys at the Los Angeles office of Latham & Watkins LLP, and specialize in environmental law. They can be contacted at lisa.binder@lw.com and maria.hoye@lw.com, or at 213/485-1234.