What’s New with TCE?

Not a lot, it seems. TCE has been in the center of a regulatory tangle going back over seven years, which has delayed the development of health criteria based on the most current health effects data. Over 15 years ago, EPA withdrew the cancer slope factors used to assess human cancer risks from TCE, because it was questioned that those values, derived from studies in rats and mice, adequately reflected the cancer hazard in humans. About seven years ago, the EPA began reassessing the science associated with the health risks of TCE, and issued in 2001 a draft report of that reassessment. That report concluded that evidence for TCE being a human carcinogen was stronger than previously believed, and that TCE was a more potent carcinogen than previously believed. After a contentious public review period with the science in EPA’s draft reassessment being closely questioned, the National Academy of Sciences took up a review of the EPA reassessment in 2004. Over a year ago, the National Academy of Sciences published its findings, validating some of EPA’s conclusions, and sending others back for further study; for example, EPA’s conclusion that TCE was a more potent carcinogen was judged by the NAS to be based on weak evidence.

EPA’s TCE web page doesn’t provide a schedule for when its risk assessment is going to be updated. There doesn’t appear to have been a lot of new data generated in the past year, based on what’s available in PubMed. One meta-analysis of occupational epidemiology of TCE exposure and liver cancer attempts to rebut the finding from the NAS study that high-dose TCE exposure, such as found in some workplaces, may be relevant to human cancer risk. This is relevant with regard to liabilities for past exposures (and is probably the origin for the study), but may eventually become a moot point. TCE releases are decreasing with time according to the TRI, which suggests that between pollution prevention initiatives and lingering concerns about groundwater contamination and exposure liabilities, businesses using metal cleaners or solvents are finding alternatives for TCE.

Another study investigated the association between TCE exposure and mutations in the von Hippel-Lindau (VHL) gene, which has been identified as a mechanism for kidney cancer. They examined several kidney cancer patients who may have had high TCE exposures in the past but didn’t observe a relationship between VHL mutations and TCE exposure. This doesn’t necessarily mean that TCE isn’t a kidney carcinogen in humans (the NAS concluded it’s likely there’s a relationship between TCE exposure and kidney cancer), but that further investigation may be needed to understand the mode of action for kidney cancer.

EPA scientists published a paper earlier this year discussing the difficulties in understanding the mode of action for TCE (in this case, with regard to liver cancer), which I suppose explains in part why a finalized risk assessment isn’t available yet. Congress is getting into the act with TCE, a development that absolutely floored me when I first heard about it back in August of this year. Senate Bill 1911 (S.1911), sponsored by Sen. Hillary Clinton and with bi-partisan support, would “amend the Safe Drinking Water Act to protect the health of susceptible populations, including pregnant women, infants, and children, by requiring a health advisory, drinking water standard, and reference concentration for trichloroethylene vapor intrusion (note: someone should remind Congress that the RfC doesn’t address cancer effects), and for other purposes”. It’s currently in the Senate Environment and Public Work Committee. Nothing has happened yet, but it’s still surprising that Congress is getting involved. Three years ago, I asked the question:

What’s next if the NAS can’t provide some good recommendations? Take it to Congress? I can’t wait to see that: “quick, we need to put aside the war on terror so we can debate this drinking water standard for TCE”.

This is one case where I hate being right.