Federal scientists say burning oil to clean up the massive Gulf spill released small amounts of toxins, but not enough to pose an added cancer risk to workers and coastal residents.

The U.S. Coast Guard set 411 fires from late April to mid-July, burning off as much as 13 million gallons of oil from BP's blown-out well that otherwise might have reached the shore. The well, before being capped, released more than 200 million gallons of oil.

Research released Friday by the EPA found concentrations of cancer-causing dioxins in 27 smoke plumes similar to those created by woodstoves or forest fires. A second team concluded that there was only a small added risk of cancer to people breathing polluted air or eating tainted fish.