Dale Sandler, chief of the epidemiology branch of the National Institute of Environmental Health Sciences, the government office heading the study, said that it was commissioned after some cleanup workers reported chest pain, headaches, breathing difficulties and other ailments that they believed were linked to the oil spill.
"There are people who are sick," Ms. Sandler said. "Are they sick from the oil? Maybe, but we don't know."
The study, funded with an initial $8 million from the government and $6 million from BP PLC, aims to follow 55,000 former cleanup workers for up to a decade. It will be the biggest study ever of an oil spill's health effects, federal officials said. It will look at everything from skin rashes to respiratory problems to potential increased cancer risk.
The BP spill poured an estimated 4.1 million gallons of oil into the Gulf between late April, when the Deepwater Horizon drilling rig exploded, and mid-July, when the leaking well was capped.
At the height of the spill cleanup, in mid-July, some 47,000 people were working on it, officials said. Some shuffled paper in offices. Some shoveled oil off beaches. Some manned boats near the site of the ruptured well, skimming and burning the slick of oil off the Gulf's surface. About 7,000 people are working on the cleanup today, officials said.
The BP money for the study comes from a $500 million fund the oil company set up to fund scientific research in the wake of the spill. BP didn't design the study and won't help conduct it, government and BP officials said. BP wanted "an independent and credible review" of any potential link between cleanup workers' heath problems and the spill, said Richard Heron, BP's chief medical officer. The government scientists overseeing the worker-health study are "very credible," he said.
The study's findings could, indirectly, raise BP's bill for the spill. Lawyers often use epidemiological studies as ammunition in lawsuits contending environmental incidents such as spills injured their clients.
But alleged victims would have to bring suits to collect any such damages. By contrast, federal law requires oil companies to pay the government lump-sum compensation for harm their spills are found to have caused the environment, from fish to marsh grass.
The spill study won't prove definitively whether BP oil caused any health problems, said scientists who helped design it. The Gulf region has so many other pollution sources, from chemical plants to boats, that proving the spill caused anyone's illness will be exceedingly hard.
Drivers pumping gas into their cars often breathe in some of the same chemicals, such as benzene, that cleanup workers may have inhaled from the spilled oil, said Maureen Lichtveld, chairwoman of the environmental health sciences department at the Tulane University School of Public Health and
Tropical Medicine and one of the experts consulted in designing the study.
It's "very difficult, in general environmental health, to really isolate a specific cause and effect," she said. But, she said, "we may get some clues."
Scientists believe some 130,000 people—most in Louisiana, Mississippi, Alabama and Florida—worked on the spill or signed up to do so, Dr. Sandler said. They hope to call about 90,000 of those people to get about 55,000 to enroll in the study.
On Feb. 28, they plan to begin mailing requests to participate in the study to the first 2,000 people. Ultimately, Dr. Sandler said, as many as 100 people will be on the ground interviewing former cleanup workers participating in the study.
Such massive studies have been done before—for breast-cancer victims, for instance. But only a handful of studies have targeted illness from oil spills, and most of those looked at only short-term impacts.
Scientists said they hoped the study would reduce risks in future oil-spill cleanups—guiding, for instance, when cleanup workers should use respirators to avoid inhaling contaminants. That question sparked disagreement during the BP spill.
"People were doing the best they could based on the information available at the time," Dr. Sandler said.