Water downstream from a ruptured Exxon Mobil pipeline that leaked oil into the Yellowstone River showed no detectable levels of toxic petroleum chemicals, according to U.S. Environmental Protection Agency documents released on Saturday.

But Montana environmental officials told Reuters that in the week since the spill at least five people have been treated at local hospital emergency rooms for symptoms including dizziness and respiratory distress after being exposed to fumes from oil.

"There could be many more," said Mary Ann Dunwell, spokeswoman for the Montana Department of Environmental Quality.

Reports of spill-related illnesses are being compiled by the state's epidemiologist.

A 12-inch Exxon pipeline carrying oil to Billings area refineries burst on July 1, dumping what the company has estimated at 1,000 barrels of petroleum into the river.

Exxon has apologized for the spill and on Friday said it had stepped up clean-up efforts.

"Our testing from the outset indicated nothing to suggest any risk to health. Exxon is pleased that the results released by the EPA confirm that no risk to health exists," Exxon spokesman Pius Rolheiser said in a statement emailed to Reuters.

Officials tested water samples, which were collected on July 4 at five sites along about 160 miles of the river corridor for three hazardous chemicals associated with crude oil considered harmful to human health at certain levels.

A statement on EPA's website said air monitoring along the Yellowstone showed no detectable levels of cancer-causing compounds linked to petroleum products.


Earlier on Saturday, Exxon submitted a draft clean-up plan of the oil spill to the EPA.

Few details of the report were immediately available, but it was expected to spell out how the oil giant would monitor the environment, clean up pollutants, restore damaged areas on the Yellowstone and dispose of hazardous wastes.

Meanwhile the U.S. House Transportation subcommittee on Railroads, Pipelines, and Hazardous Materials announced that it would examine pipeline safety following the rupture that released crude oil into one of America's most pristine rivers 150 miles downstream from Yellowstone National Park.

Federal officials say shoreline contamination has been observed over an area stretching at least 240 miles downstream from the site of the burst pipeline.

Residents whose properties have been soiled by toxic petroleum chemicals have said that EPA and Exxon officials were unresponsive to their concerns.

Montana Governor Schweitzer cited those complaints on Thursday when he pulled the state from an emergency response panel led by the EPA and opened an office to investigate the spill and to aid residents.

Schweitzer, who has threatened to hold Exxon "liable in court," has also accused Exxon of underestimating the amount of oil spilled.

High water in the Yellowstone has hindered government and Exxon efforts to determine the cause of the failure of the pipeline, which was buried in the riverbed. Exxon said it shut down pumps on the pipeline to stop the oil flow within six minutes of discovering that something was wrong.