Published: May 07, 2010 4:52 PM EDT

 NEW ORLEANS  - The huge oil slick drifting in the Gulf of Mexico is not only a serious threat to marine and animal life on the Gulf Coast; experts are now saying the oil slick may pose dangers to people.

State and federal authorities are preparing to deal with a variety of hazards to human health if and when the full brunt of the toxic mess washes ashore.

The list of potential threats runs from temporary, minor nuisances such as runny noses and headaches to long-term risks such as cancer if contaminated seafood ends up in the marketplace. Public health agencies are now monitoring air quality, drinking water supplies and seafood processing plants and advising people to take precautions.

The Centers for Disease Control and Prevention is working with epidemiologists in the Gulf states to develop studies of health repercussions from the oil spill.

Giant box close to being over oil-spewing well

A 100-ton concrete-and-steel box plunged toward a blown-out well at the bottom of the sea Friday in a first-of-its-kind attempt to stop most of the gushing crude fouling the Gulf of Mexico.

Douglas Peake, first mate of the supply boat that brought the box to the site, confirmed he had received a radio transmission from the nearby vessel lowering the device that it would be in position over the well soon. The transmission said undersea robots were placing buoys around the main oil leak to act as markers to help line up the 40-foot-tall box. But nearly seven hours later, there was no word from officials on whether it had made it to the bottom.

Once the contraption gets to the seafloor, underwater robots will secure it over the main leak at the bottom, a process that will take hours.

If the delicate procedure works, the device could be collecting as much as 85 percent of the oil spewing into the Gulf and funneling it up to a tanker by Sunday. It's never been tried so far - 5,000 feet - below the surface, where the water pressure is enough to crush a submarine.

"We haven't done this before," David Nicholas, a spokesman for oil giant BP LPC, which is in charge of the Gulf cleanup. "It's very complex and we can't guarantee it." BP was leasing the drilling rig Deepwater Horizon when it exploded 50 miles offshore April 20, killing 11 workers and blowing open the well.

An estimated 200,000 gallons a day have been spewing in the nation's biggest oil spill since the Exxon Valdez disaster in Alaska in 1989.

The containment device will not solve the problem altogether. Crews are still drilling a relief well and working on other methods to stop the well from leaking. The quest took on added urgency as oil reached several barrier islands off the Louisiana coast, many of them fragile animal habitats. Several birds were spotted diving into the oily, pinkish-brown water, and dead jellyfish washed up on the uninhabited islands.

"It's all over the place. We hope to get it cleaned up before it moves up the west side of the river," said Dustin Chauvin, a 20-year-old shrimp boat captain from Terrebonne Parish, La. "That's our whole fishing ground. That's our livelihood."

Out at sea, the crew of the semi-submersible drilling vessel Helix Q4000 waited hours longer than expected to hoist the containment device from the deck of the Joe Griffin supply boat because dangerous fumes rose from the oily water.

Joe Griffin Capt. Demi Shaffer told an Associated Press reporter aboard his boat the fear was that a spark caused by the scrape of metal on metal could cause a fire. Crew members wore respirators while they worked. Conditions were safe enough to allow the crane to lift the device into the Gulf after 10 p.m. CDT, dark oil clinging to its white sides as it entered the water and disappeared below the surface. The box - which looks a lot like a peaked, four-story outhouse, especially on the inside, with its rough timber framing - must be accurately positioned over the well, or it could damage the leaking pipe and make the problem worse.

BP spokesman Doug Suttles said he is not concerned about that happening. Underwater robots have been clearing pieces of pipe and other debris near where the box will be placed to avoid complications.

"We do not believe it could make things worse," he said. Other risks include ice clogs in the pipes - a problem that crews will try to prevent by continuously pumping in warm water and methanol - and the danger of explosion when separating the mix of oil, gas and water that is brought to the surface.

"I'm worried about every part, as you can imagine," said David Clarkson, BP vice president of engineering projects. If the box works, a second one now being built may be used to deal with another, smaller leak from the sea floor. Meanwhile, a huge oil slick is floating in the Gulf, and residents of Louisiana, Mississippi, Alabama and Florida are anxiously waiting to learn when it might come ashore.

Seas were calm Friday, and the Coast Guard hoped to continue skimming oil from the ocean surface, burning it at sea and dropping chemicals from the air to break it up. Oil from the spill is extending west around the Mississippi Delta, according to a radar image taken Wednesday night by a Canadian satellite.

That extension looks like a finger reaching out from the main patch, imaging expert Hans Graber of the University of Miami said Friday. The main oil slick has been shifting to the northwest, encroaching on Chandeleur Sound, which lies between the delicate Chandeleur Islands and Mississippi Delta wetlands, he said.

A federal judicial panel in Washington has been asked to consolidate at least 65 potential class-action lawsuits claiming economic damage from the spill. Commercial fishermen, business and resort owners, charter boat captains, even would-be vacationers have sued from Texas to Florida, seeking damages that could reach into the billions.

"It's just going to kill us. It's going to destroy us," said Dodie Vegas, who owns a motel and cabins in Grand Isle, La., and has seen 10 guests cancel.