On September 28, 2011, the U.S. Environmental Protection Agency (EPA) released its long-awaited final health assessment (Assessment) for trichloroethylene (TCE). Unlike EPA’s prior classification of TCE as a probable human carcinogen, EPA now is classifying TCE as carcinogenic to humans through all routes of exposure. The Assessment also establishes health benchmarks for noncancer effects by the oral and inhalation routes of exposure.
EPA submitted its new Assessment to the Integrated Risk Information System (IRIS). IRIS is a human health assessment database containing EPA’s evaluations on health effects that may result from exposure to chemicals. IRIS provides foundational information upon which EPA offices rely in the development of regulatory standards, such as under the federal Safe Drinking Water Act, the federal Clean Water Act, and the federal Clean Air Act.
According to EPA, the Assessment will provide federal, state, local, and other policy makers with the latest scientific data to make decisions about cleanup and other actions to protect human health. The Assessment values may have a short-term impact at some federal Superfund sites, where they may be used to propose new TCE screening and cleanup levels. Regulators may look to the TCE screening levels to evaluate the threat or presence of TCE vapor intrusion and TCE groundwater contamination. As a result of the Assessment, EPA’s Office of Water likely will review its Maximum Contaminant Level standard for TCE, the maximum level of TCE permitted in drinking water supplied by a public water system.
The final Assessment values for TCE have not yet been promulgated into a rule through notice and comment rulemaking. While the IRIS toxicity values are not enforceable standards, IRIS is designed to provide an agency-wide consensus assessment, and therefore may be accorded substantial weight by the EPA offices, as well as by other federal, state, and local authorities.
The chemical and prior risk assessments
TCE is a volatile organic compound that was used widely in the twentieth century by the military and industry as a degreasing solvent for machine parts and aircraft. It is still used in consumer products such as adhesives, typewriter correction fluid, paint, and spot removers. Due to its former widespread usage, TCE has been reported in air, soil, and water at thousands of current and former manufacturing facilities, military installations, and waste sites around the country. TCE is one of the most common compounds of concern in groundwater and has been found at 60 percent of the sites on the Superfund National Priorities List (NPL).
Exposure to TCE can occur in several ways, including ingestion and dermal contact (e.g., drinking or showering in water containing TCE) and inhalation (breathing air containing TCE). EPA issued its first TCE health assessment in 1987, when the agency concluded that TCE was a “probable human carcinogen,” meaning that data were adequate to demonstrate carcinogenic potential to humans, but did not reach the evidentiary threshold to consider TCE carcinogenic to humans. In 1989, EPA withdrew the “probable human carcinogen” classification of the 1987 assessment because of issues raised by EPA’s internal scientific peer review group, the Science Advisory Board (SAB).
In 2001, EPA released a revised draft risk assessment for TCE, finding TCE to be “highly likely to produce cancer in humans.” In response, EPA recommended stringent new cancer slope factors that treated TCE as two to forty times more potent than previously thought. Government and industry criticized the 2001 draft assessment on the basis that EPA supported its conclusions with limited and indeterminate scientific data. The National Aeronautics and Space Administration and the Departments of Defense (DOD) and Energy joined with EPA to co-sponsor a scientific consultation review of the 2001 draft assessment, which was performed by the National Research Council of the National Academy of Sciences (NAS).
In July 2006 NAS issued its final report. The academy found that the evidence on carcinogenic risk and other health hazards from exposure to TCE had strengthened since the 2001 draft risk assessment. Accordingly, NAS recommended that EPA finalize its risk assessment with currently available data in order to expedite risk management decisions.
Following the 2006 National Academy of Sciences Report, EPA hosted a TCE symposium and submitted issue papers for further review. Based on these data, EPA released a draft IRIS toxicological review for TCE in October 2009, and requested EPA’s internal SAB to conduct a peer review of the draft assessment. In January 2011, SAB released its review, reporting that the SAB panel supported EPA’s scientific approaches to the risk assessment. After slight revisions recommended by the SAB, EPA released its final 1,200 page Assessment in September 2011.
The current risk assessment
The 2011 Assessment finds that TCE is a known human carcinogen. In the Assessment, EPA referenced its 2005 Guidelines for Carcinogen Risk Assessment, and now classifies TCE as “carcinogenic to humans by all routes of exposure.” The guidelines recommend this classification “when there is convincing epidemiologic evidence demonstrating causality between human exposure and cancer.” EPA maintains that the Assessment is based on convincing evidence of a causal association between TCE exposure in humans and kidney cancer. EPA determined there to be less convincing epidemiologic evidence linking TCE exposure to non-Hodgkin lymphoma. EPA concluded that TCE is carcinogenic by a mutagenic mode of action for induction of kidney tumors. The mutagenic identification sparked controversy, as such a classification would suggest that early life exposures to TCE could increase the risk of eventual cancer.
With respect to non-cancer health effects, EPA’s Assessment found that TCE exposure is associated with harm to the central nervous system, kidneys, liver, the reproduction system, the immune system, and the developing fetus.
Legal limitations and criticisms of IRIS final health assessments
The TCE toxicity values as published in the IRIS database are not legally binding. EPA has reiterated the limitations of IRIS values in both internal and public statements. For example, in a 1994 EPA internal memorandum, EPA stated that, “IRIS values are not entitled to conclusive weight and shall not be made legally binding in the context of any other rulemaking action;” EPA further stated, “EPA or any state agency that uses IRIS should not rely exclusively on IRIS values.” Memorandum from the U.S. EPA, Guidance on Use of Integrated Risk Information System (IRIS) Values (Aug. 26, 1994).
EPA also has acknowledged publicly that IRIS values are not entitled to conclusive weight. Former Administrator Christine Whitman stated that, “EPA recognizes that IRIS is not a comprehensive toxicological database…IRIS values are not rules adopted after notice and comment rulemaking, although….public comments are solicited, IRIS values are not legally binding and are not entitled to conclusive weight in any rulemaking.” Moreover, “EPA or any State agency that uses IRIS should not rely exclusively on IRIS values but should consider all credible and relevant information that is submitted in any particular rulemaking.” 66 Fed. Reg. 46,929 (Sept. 7, 2001). The D.C. Circuit supported this finding, stating that “the [IRIS] database by itself has no preclusive effect; the data in the database constrain no one until so applied in a particular rule.” Chemical Mfrs. Ass’n v. EPA, 28 F.3d 1259, 1263 (D.C. Cir. 1994).
EPA has been criticized by both industry and other governmental bodies for the methods of evaluation and lack of clarity in some IRIS assessments. While the 2006 NAS Report largely approved of EPA’s draft TCE assessment, NAS has not given passing marks to other draft chemical assessments. For instance, in April 2011, after reviewing the draft Formaldehyde Assessment, NAS found that EPA failed to support some of its conclusions regarding health problems linked by EPA to formaldehyde. NAS also questioned EPA’s methodology.
After issuing a critical 2008 report on IRIS, the Government Accountability Office (GAO) added IRIS to its annual “high risk” list of troubled federal programs in 2009. A December 2011 GAO report noted continuing problems with IRIS.
Criticisms of IRIS have led EPA to take steps to modify the IRIS system. In July 2011, EPA announced changes to strengthen the IRIS program in response to recommendations from NAS, intending to focus on quality, transparency, and scientific rigor.
Practical consequences of the risk assessment
EPA reports that the TCE toxicity values in the Assessment will be considered in the following ways: (i) establishing cleanup methods at the 761 Superfund sites where TCE has been identified as a contaminant, (ii) understanding the risk from vapor intrusion where TCE vapors move from contaminated groundwater and soil into the indoor air of overlying buildings, (iii) revising EPA’s standard for TCE as part of the carcinogenic volatile organic compounds group in drinking water, and (iv) developing appropriate regulatory standards limiting the atmospheric emissions of TCE—a hazardous air pollutant under the Clean Air Act.
When the new TCE values will be used as EPA forecasts is unclear. DOD does not expect an immediate impact from EPA’s Assessment. About 1,400 DOD sites across the nation are contaminated with TCE, including military bases and depots. A DOD spokesperson remarked that the Assessment, “may or may not lead to eventual changes in cleanup standards or drinking water Maximum Contaminant Levels,” and that, “such changes, if any, would likely take years to develop and finalize.” Id. Still, DOD has undertaken TCE reduction efforts; DOD reported, “the Army reduced releases of TCE from 214,223 pounds in 1994 to 62,495 pounds by 2008.” Id. The Air Force environment chief Terry Yonkers noted in a November 29, 2011, speech that the Air Force could face up to $15 billion in added cleanup costs if EPA modifies the groundwater standards for TCE based on the Assessment.
Though it likely will take years for EPA to promulgate new enforceable standards that rely upon the new Assessment, many impacts of the Assessment will manifest sooner. For example, the revised TCE values likely will be used on an ad hoc basis in regional EPA offices. EPA Region 9 recently stated that it may announce changes to the regional screening levels, non-binding tools for screening preliminary soil or groundwater levels at contaminated sites, to reflect the new TCE exposure recommendations as early as May 2012.
Editor’s Note: On February 10, 2012, EPA announced a second risk assessment revision for another common industrial solvent, tetrachloroethylene (PCE or perc). As the authors indicate with respect to the TCE risk assessment, risk assessment revisions potentially can have major impacts on users of such solvents.