Tests: Oil spill's most toxic compounds dissipated

By MATT VOLZ | August 4, 2011 | 4:00 PM EDT

Clean-up crews break for the day after working to soak up oil from a back channel of the Yellowstone River, Sunday, July 10, 2011, near Laurel, Mont. Federal and state officials separately release the results of air, soil and water samples taken downstream from a pipeline break in the Yellowstone River. Montana officials on Wednesday, Aug. 3, 2011, laid out plans to map the "invisible spider web" of pipelines crossing beneath state waterways in the wake of last month's Exxon Mobil Corp. pipeline break under the Yellowstone River. (AP Photo/Julie Jacobson)

HELENA, Mont. (AP) — State and federal officials say the most toxic compounds contained in an estimated 50,000 gallons of spilled oil dissipated quickly after last month's Yellowstone River pipeline break.

Gov. Brian Schweitzer and the Environmental Protection Agency said Thursday what was left behind are less volatile gobs of crude.

The EPA and the state released the results of air, water and soil samples taken after the July 1 pipeline break, aiming to alleviate concerns about the risk to public health.

The spill's fumes have sickened some residents. They worried the oil could seep into their drinking water and harm crops and livestock.

One resident, Jim Swanson, says that he's not convinced by the results. He hired a private company to take his own soil and water samples, and is awaiting the results.