Toxicology Expert Witness – MTBE Future Cancer

MtBE and future Cancer? Oh give me a break!
By John Mennear, Ph.D.

Its real name, methyl tertiary butyl ether, may sound absolutely carcinogenic and it smells so bad that a single whiff will bring rotten eggs to mind. And to make matters worse, it is appearing in places where it shouldn’t, – most disturbing of all, in well water.

But contrary to the ill-founded and scientifically unsupported opinions of some activists, numerous plaintiff attorneys and their assembled experts, the gasoline additive that was initially introduced to help reduce air pollution, is not a human cancer risk. There simply is no credible scientific evidence to support claims of increased “risk of future cancer” because of people being exposed to MtBE.

It is true that when large groups of rats spend much of their time inhaling enough MtBE to make them fall asleep some of the males get kidney cancer. But it is equally true that identically exposed females don’t get kidney cancer. This is because male rats are the only animals that have the biochemical mechanism that predisposes their kidney cells to cancer after exposure to, among many things, MtBE. So the MtBE kidney cancer is a male rat specific tumor with no predictive validity for extrapolation to humans.

It is also true that in 1995 a group of Italian scientists published the results of an experiment in which rats were force-fed enormous doses of MtBE. These authors claimed MtBE caused leukemia and testicular cancer. The researchers initially agreed to have their results reviewed by a group of American experts but five years later they still haven’t produced the data. Consequently, few in the International scientific community are willing to afford credence to the Italian’s data and interpretations.

Finally, most important human carcinogens cause cancer by first damaging cellular DNA and converting normal cells to neoplastic cells. Despite repeated attempts to prove otherwise, MtBE does not damage DNA. Typically, chemicals that cause cancer without damaging DNA exert their effects only after prolonged exposure to extreme and cell killing doses. Because

of its intense and offensive odor (and taste) humans will not tolerate either air or water concentrations sufficient to produce the cell damage that initiates the cascade of events leading to cancer.

In 1997 I stated that, “The carcinogenic effect of MtBE in rats and mice has been recognized and defined. The human cancer risk attending either occupational or incidental exposure to MtBE is so small that it is essentially non-existent.” (Toxicology and Environmental News, 4, 139-147; Risk Analysis, 17, 673-681). Since then, national and international scientific bodies have voiced the same conclusion (National Science and Technology Council, June, 1997; World Health Organization, 1998; National Toxicology Program, 1998; California Environmental Protection Agency, 1998; International Agency for Research on Cancer, 1999; and the US Environmental Protection Agency, 1999). The bottom line is that drinking water should be MtBE-free and organizations that cause pollution should foot the bill for cleanup. But there is no credible scientific data to support the idea that people exposed to trace levels of MtBE are more likely than anyone else to develop cancer or any other health problems.


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