MTBE – a cause of cancer?

A US Environmental Protection Agency (EPA) draft risk assessment says MTBE, the gasoline additive that has contaminated drinking water in at least 29 US states, is a "likely" human carcinogen, according to agency sources.

An EPA official who reviewed an earlier version of the document told the US Environmental Working Group (EWG) that the risk assessment links MTBE to cancers such as leukemia and lymphoma.

Previously, EPA had classified MTBE as a "possible" cause of cancer, and concerns about contamination centred on the fact that in small doses its foul stench renders water undrinkable.

The EPA official said the document's authours completed their draft more than a year ago. It has been circulating within the agency for review and has already been approved by the US Office of Research and Development's National Center for Environmental Assessment. Once all EPA divisions have signed off on it, it must still go through external review.

"People have been trying to get this out of the agency forever," said the official.

If approved, the finding will rock the current debate in the US Congress over whether the oil companies who make and use MTBE should be held responsible for cleaning up drinking water contaminated by the chemical leaking from underground gasoline storage tanks. According to state water agencies' records compiled by EWG, MTBE has been detected in more than 1,800 water systems across the US.

The American Water Works Association and the Association of Metropolitan Water Agencies released studies last month estimating nationwide cleanup costs at between $25 billion and $33 billion, and possibly reaching $85 billion.

The finding that MTBE is a likely carcinogen would add urgency to cleanup efforts, causing costs to soar.

The EWG says that the US House has passed an energy bill, pushed by Majority Leader Tom DeLay of Texas, that would bar communities and water systems from suing MTBE makers for knowingly manufacturing and distributing a defective product - even though documents from two California lawsuits show the oil industry knew as early as 1979 that the compound was a threat to water supplies but still pushed for its use as a gasoline additive to make fuel burn cleaner.

"We knew the idea to exempt MTBE makers from lawsuits was bad news for taxpayers. Now EPA is learning how dangerous it would be for public health," said EWG President Ken Cook. "No matter how the risk assessment finally comes out, this is clearly not the time to let the makers of this chemical off the hook."