An Overdue Welcome to the Blogroll

Since they’ve been kindly linking to me for quite awhile and lately been sending some traffic my way, let me correct an overdue situation and welcome The TCE Blog to the IA blogroll. We may not always see eye-to-eye on specific issues, but I feel that in our own ways, we’re both trying working towards a common goal.

More of the TCE Story Missed by the LA Times

There are a lot of apprehensive people living over TCE vapor plumes, or who have been drinking water at one time was contaminated with TCE, and they need some reliable information about the potential health risks involved. What they get from the LA Times is this:

Following four years of study, senior EPA scientists came to an alarming conclusion: The solvent, trichloroethylene, or TCE, was as much as 40 times more likely to cause cancer than the EPA had previously believed.

In the blink of an eye, this factoid has spread nearly everywhere, Wikipedia included.

How real is this? Let’s take a stab at figuring out where it might come from.

A little bit of background first: one of the tools used in risk assessment is a cancer potency factor (or slope factor). The slope factor is used to calculate the increased cancer risk from exposure to a chemical. Essentially, the cancer risk associated with a scenario is calculated by multiplying the slope factor by the level of chemical exposure.

In 1985, EPA estimated an oral slope factor for TCE of 0.011 kg-day/mg, based on the tumor incidence in an animal bioassay. This value was removed from IRIS in 1989, when EPA’s Science Advisory Board criticized EPA’s classification of TCE as a probable human carcinogen. In its 2001 reassessment, EPA presented a range of slope factors from 0.02 to 0.4 kg-day/mg. Some people (and most likely not EPA scientists, or at least not the ones who really understand this stuff) simply took the high-end slope factor from the 2001 assessment, divided it by the older number, and concluded EPA had found that TCE was 40-fold more carcinogenic in the intervening time between the original assessment in 1985 and the 2001 reassessment.

It’s probably not that simple.

In 1985, the slope factor for TCE was developed from liver tumors in mice, based on indirect evidence (here and here) – I can’t lay hands right now on the primary reference, EPA’s 1985 health assessment (Health Assessment Document for Trichloroethylene, EPA/600/8-82/006F)*. Also, I’m assuming that the 1976 NCI cancer bioassay was the one used by EPA based on chronology – the repeat TCE cancer bioassay using epichlorohydrin-free TCE was not published until 1990. The doses in mice were extrapolated to human body size, then a linear extrapolation model was used to calculate the slope factor that provided an upper bound of the risk associated with exposure to TCE.** The process is described in more detail in EPA’s old 1986 cancer risk assessment guidelines.

In 2001, the value on the upper end of the slope factor range was estimated from relative risk ratio for non-Hodgkins lymphoma observed in an epidemiological study of drinking water exposures in 75 New Jersey communities. The relative risk ratio of 1.4 was combined with the U.S. background incidence of non-Hodgkins lymphoma and the average TCE concentration in drinking water to calculate a unit risk factor (0.00001 per ug/L) which was then converted to a slope factor using the standard adult body weight (70 kg) and drinking water ingestion (2 L/day) assumptions.

One purpose for slope factors is to be able to compare the potencies of different carcinogens, but the comparison isn’t terribly meaningful without these qualifiers attached to them. The more important point, which the Times didn’t bring out, is that EPA’s reassessment included evaluation of the risks potentially associated with non-Hodgkins lymphoma and leukemia. Concerns appear about these effects appear in part to have emerged from the potential drinking water exposures in Woburn, MA (of “A Civil Action” fame). The early epidemiological studies (published after EPA’s 1985 health assessment) apparently were considered to be inconclusive. However, the literature shows more epidemiological studies being conducted in the 1990s of populations potentially exposed to TCE (among other contaminants) in drinking water. So, the story isn’t so much a matter that TCE is a more potent carcinogen than previously believed (that may or may not be the case), but that further research has potentially identified some additional health effects associated with TCE exposure.

I’m disappointed with the LA Times TCE series for a couple of reasons. First, instead of the “40-times-more-carcinogenic”, lazy-man’s hazard evaluation; they would have provided more of a service to their readers by turning to an authoritative review of TCE, such as from the NTP Report of Carcinogens, and producing a readable summary of it (or perhaps even talking with someone at the UCLA School of Public Health, and getting a quick TCE tutorial). Second, for not conducting some real investigative journalism where it was really needed; you get hints and assertions about the problems with the TCE review process, but never any real evidence or narrative about what actually happened (that’s a topic for another post – this one’s long enough already. I’m not quite done with the Times series yet. . .). Producing those sorts of stories is why we really need the mainstream media, because they have the resources to investigate them. But, I feel as if the Times let us down in this case.

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*EPA has a lot of older documents online here, including the 1987 addendum; but not the 1985 report.

**For slopes estimated using this 1986 methodology (still in use for a lot of chemicals), EPA includes the qualifier that the procedure produces, “. . . a plausible upper limit to the risk that is consistent with some proposed mechanisms of carcinogenesis. Such an estimate, however, does not necessarily give a realistic prediction of the risk. The true value of the risk is unknown, and may be as low as zero.” I’ve always thought this phrase should be inserted as a footer on each page of a risk assessment report.

Nukes in Our Future?

I can’t title this “Going Nuclear”, because the WaPo already did it. Patrick Moore, one of the founders of Greenpeace has experienced an epiphany about nuclear power, concluding now that it poses less of a risk than global climate change potentially resulting from greenhouse gas emissions from fossil power sources. He focuses on the health and safety considerations – it’s not as dangerous as we once thought – as the primary rationale. For my part, I’ve never been either strongly in support or opposition to nuclear power based on the safety grounds. It’s just one of many useful technologies that could cause human or ecological catastrophe if not managed sensibly. The idea is not to simply worry about them, because that’s a recipe for curling up into a little ball of despair, but to create the infrastructure, philosophy and commitment to manage their risks (including doing without that technology if there is a good substitution or it isn’t really needed).

I can’t wait to see the froth this creates in the blogosphere.

There isn’t any reason to get too excited, because it ain’t happening yet, and the devil’s in the details. I’d be interested in seeing what the lifecycle costs and impacts look like (fuel cycle, plant safety and security, environmental and waste management, plant decommissioning, etc.) before concluding how cost-effective it is. There are a lot of established commercial interests without nuclear portfolios or experience who will use their political and public relations clout to delay phase out of fossil fuels and reintroduction of nuclear energy, at least until they can be competitive in the nuclear field. Transitioning to nuclear power doesn’t reduce the need for energy conservation, replacing fossil-fuel transportation or agriculture, or making the other changes needed to move to a sustainable society. The closing message, which wasn’t something I saw in the editorial, is that increased reliance on nuclear power over fossil fuels isn’t a ready-made excuse to continue “business as usual”.

Postscript, Monday, April 17, 2006:

Steve Gilliard offers this reminder of potentially the largest impediment to the resurgence of nuclear energy in this country – the image of it ingrained in the collective subconscious from popular depictions over the past generation, including Them!, The China Syndrome, and Blinky, The Three-Eyed Fish.

A Daily Kos diarist also notes that using Moore’s credentials as a founder of Greenpeace as evidence that the tide has turned for nuclear power is a little thin, since he currently is a communications consultant for industries with environmental problems. I guess he’s also discovered that, while championing noble causes looks good on the resume, the pay really sucks.

Edited to correct a reference from "fission" to "fossil".

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).

The LA Times Coverage of Trichloroethylene (TCE)

The LA Times two-part article on trichloroethylene has brought me back to the blogosphere out of day-job exile. I'm pleased the topic is getting some coverage in a major newspaper. I was intrigued by Dr. Ozonoff's analogy that inaction on reducing TCE exposure could be a WTC disaster in slow motion, a vivid way of depicting the potential risks (risk assessment needs to make better use of imagery for displaying and communicating health risks). It's prompted me to start doing the arithmetic to explore it more fully.

But as a student of TCE regulatory history, reading the Times series was like looking at my reflection in a fun-house mirror. Stay tuned for examples.