The TCE Story the LA Times Missed

The TCE story is important because it encapsulates everything that’s troubling about the glacial pace of environmental health standard setting: complex and time consuming risk assessment processes; lack of transparency in decision making; limited public involvement (reliance on the “decide, announce, defend” mode of decision making, coupled with the inability or unwillingness of many in the public to engage meaningfully in the debate); insufficient application of risk communication models, resulting in insufficient comprehension of health risk comparisons on the part of many stakeholders (affected communities and political leaders); difficulty in deciding how to manage risks under uncertainty – cost-risk-benefit analysis versus precaution.

At what point is it an honest scientific debate regarding appropriate standards for managing health risks from TCE exposure? At what point does is it no longer a debate, but the manufacturing of uncertainty to defer decision making? How much time should the process require to obtain enough information for managing risks? How much time is too much – allowing the occurrence of potentially significant adverse effects before implementation of control measures? What are the appropriate standards of protectiveness? Has the health judgments underlying those standards been communicated to the public, to allow their participation in the debate (in other words, how clearly is it understood that risk management actions do not leave us free from risk)? All are important topics that we need to come to grips with if we’re going to have any success as a society in managing health risks associated with chemicals in the environment. By writing a story that’s both thin on facts and that depicts this topic as conflict between protagonists and antagonists (yes, C.P. Snow’s “Two Cultures” are apparently still alive and kicking), the LA Times missed a great opportunity to better inform the public debate about environmental health risks and their management.

The first paragraph in the March 29th article alerted me that I was going to have an out-of-body experience subjecting me to a TCE alternate reality:

After massive underground plumes of an industrial solvent were discovered in the nation's water supplies, the Environmental Protection Agency mounted a major effort in the 1990s to assess how dangerous the chemical was to human health.

This is a bit of dramatic license creating the master narrative that the whole of Superfund, and several of health effects research and risk assessment programs conducted by various EPA offices were caught flat-footed by TCE in groundwater. The discovery of TCE in groundwater predates the passage of Superfund in 1980 - I can recall reports in 1979 of TCE detected in groundwater at McClellan Air Force Base in my then-hometown of Sacramento, California. As an aside, my first job out of college in 1977 involved analyzing environmental samples including groundwater for the volatile soil fumigant 1,2-dibromo-3-chloropropane (DBCP) using gas chromatography. DBCP has similarities to TCE, as another volatile organic compound that can readily migrate through soil. The mid to late 1970s seemed to be the onset for detecting trace levels of VOCs in groundwater, when GC methods became sensitive enough to detect sub-part per million concentrations. I think people were quite aware of TCE in groundwater long before the 1990s.

Also, while it’s correct to say that the EPA mounted a major effort starting in the 1990s to better understand TCE health risks, as written, this seemingly implies that people were unaware of the health risks of TCE before the 1990s. A more detailed look at this chronology shows a more complex story.

The awareness that TCE was potentially a human carcinogen started in the mid-1970s – this can be dated reasonably accurately by looking at the NIOSH criteria documents for TCE, one published in 1973 with virtually no mention of carcinogenicity and the update published in 1978 which focused on TCE cancer risks. The 1978 criteria document incorporated the results from an NCI animal bioassay published in 1976.

In 1985, EPA prepared a health assessment document for TCE (with an update in 1987), as a reference for various regulatory programs. The range of adverse effects was addressed in this document, but the focus was on TCE carcinogenicity. The cancer risks from TCE from ingestion and inhalation exposure pathways were evaluated using EPA’s newly published Guidelines for Carcinogen Risk Assessment. EPA judged TCE to be a “probable” human carcinogen based on inadequate epidemiological evidence in humans and sufficient evidence in laboratory animals. “Probable” was the second-to-the-highest rank on EPA’s spectrum of weight of evidence for human carcinogenicity used at the time; this went from “known”, “probable”, “possible”, “not classifiable” and “evidence of noncarcinogenicity”. By comparison, substances such as arsenic, vinyl chloride and benzene were classified as known human carcinogens. EPA also developed a quantitative estimate of carcinogenic potency, and ranked TCE in the lowest quartile of potency among the 58 carcinogens that had been assessed at this time.

Shortly after, this information was uploaded onto EPA’s Integrated Risk Information System (IRIS), and was available for use in making regulatory decisions concerning emissions or discharge limits and site cleanup decisions. EPA’s Science Advisory Board’s review of the cancer risk assessment concluded that TCE probably should not be classified as a probable human carcinogen, but is somewhere along the continuum between “probable” and “possible”. Following this opinion, EPA removed the carcinogen classification and potency estimates from IRIS, in 1989. I recall several years ago reading this bit of news in a response from the Superfund Technical Support Center to an information request – someone was looking for TCE cancer slope factors for a baseline risk assessment (which were no longer on IRIS, meaning you had to ask EPA how you were supposed to characterize TCE risks. . .). I saw confirmation of it years later in a brief history written by the Halogenated Solvents Industry Association, found in an obscure location (buried among the comments on the 2003 OMB report on the cost-effectiveness of federal regulations).

Some years later (HSIA says mid-1990s, which doesn’t connote an enormous sense of urgency), EPA sponsored a collaborative approach to the TCE risk assessment involving experts from government, academia and industry, which culminated in the publication of 16 state-of-the-science papers in Environmental Health Perspectives in 2000. In its introduction to the series, EPA stated that the TCE risk assessment approach differed from assessments conducted over the previous years, by placing more reliance on mode-of-action and pharmacokinetic data, which mirrored the evolution in EPA risk assessment guidance throughout the 1990s.

EPA published its TCE risk assessment in draft in September 2001, incorporating findings from the state-of-the-science review. Major findings from the assessment included a stronger relationship between TCE exposure and human cancer, and a revised quantitative risk assessment presenting a range of cancer slope factors, including a value for characterizing the risk to sensitive subpopulations with cumulative exposures. According to HSIA’s history (I’ve had no success yet finding other versions of the following account for comparison), the risk assessment engendered controversy even before it was published, with HSIA alleging that EPA did not address problems with the assessment identified during pre-publication peer review. Within days of publication of the draft risk assessment, a letter from six of the authors of the state-of-the-science papers was sent to then-EPA Administrator Christine Todd Whitman, stating their disagreement with several of the findings from the risk assessment.

During 2002, EPA solicited public comments on the TCE risk assessment, and requested that it be reviewed by the Science Advisory Board. While the industry and DOD comments roundly criticized the document, the SAB viewed it more favorably, commending EPA for employing ground-breaking risk assessment approaches and advising the agency to revise and complete the document. SAB offered the following caution:

Because the draft assessment breaks ground in several areas and sets important precedents, 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. The Board notes that public comments have raised valid concerns the Agency should carefully address. The Panel urges the Agency to review and address the public comments it received on the review draft, especially those from experts who had conducted research related to the assessment of TCE's health risks and whose reviews had been published in a supplemental issue of Environmental Health Perspectives (Volume 108, Supplement 2, May 2000).

The story gets a bit murkier for me, past 2002. I haven’t found a transparent discussion of the decisions leading up to involving the National Academy of Sciences in the TCE risk assessment, and unfortunately, the LA Times provides no help in clarifying matters (more on that later).