A cancer-causing component of oil has been detected in the drinking water supply of a city just downstream from a crude oil spill that entered the Yellowstone River.
Elevated levels of benzene were found in water samples taken from a treatment plant that serves about 6,000 people in an agricultural community in Montana near the North Dakota border, officials said.
Scientists from the federal Centres for Disease Control and Prevention say the benzene levels are above those recommended for long-term consumption but don't pose a short-term health hazard.
Read: Beware of benzene
Truckloads of bottled water were coming in Tuesday, and residents were warned not to drink or cook with water from their taps.
Some residents criticized the timing of the Monday advisory, which came more than two days after 50,000 gallons (189,000 litres) of oil spilled from a break in 12-inch (30 centimetre) pipeline owned by Wyoming-based Bridger Pipeline Co. It emerged as a concern over the response to the accident.
Adding to the frustrations was uncertainty over how long the water warning will last and why company and government officials still don't know how to remove crude trapped beneath the ice-covered Yellowstone River.
Representatives from Montana and the U.S. Environmental Protection Agency had said earlier that preliminary tests of the city's water did not show cause for concern. The water treatment plant operated until Sunday afternoon.
Additional tests were ordered Monday after residents complained of the petroleum- or diesel-like smell from their tap water. That's when the high levels of benzene were found.
Benzene was found in the range of 10 to 15 parts per billion, said Paul Peronard with the EPA. Anything above 5 parts per billion is considered a long-term risk, he said.
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Image: Expert analysis of water from Shutterstock