Even more alarming, the oil - of a type used to power ships and boilers - will allow pollutants like the mercury that nearby industries have dumped into the waters to enter the food chain, the experts said.

"If you take into account the ecosystems surrounding the spill, it's the worst accident ever in Brazil and comparable to the one in Alaska," Roberto Kishinami, the director in Brazil of international environment group Greenpeace, told Reuters.

Wildlife and the fishing industry in Alaska have still not fully recovered from the 1989 Exxon Valdez shipwreck that dumped 300,000 barrels of crude into Prince William Sound.

Kishinami said that even though the Brazil spill was only a fraction of the size of the one in Alaska, the world's worst petroleum accident, it was on a similar scale in terms of damage because it was close to land in a heavily fished area.

According to Brazil's giant state oil company, Petrobras, the ground shifted under a high-pressure pipeline in the bay, tearing it apart at the seams and releasing more than 1 million litres of oil from its Reduc refinery.

The Brazilian government's environmental regulatory agency, IBAMA, has issued a preliminary report that predicts at least a 10-year recuperation period for the bay, which abuts a sensitive, swampy mangrove reserve where shellfish were spawning when the pipeline gave way.

LARVAE DIED QUICKLY

Most of the larval-stage marine life was killed off in just a few hours, but the birds, fish and even the fishermen who depend on them for food and income will suffer for years to come, the report said.

Petrobras, which until recently had unfettered access to and power over all of the country's petroleum resources, has had to issue an unprecedented public apology for the accident and accept a record $28 million fine.

Now facing competition from more media-savvy international oil firms, the company - after an initial period of confusion - has owned up to its responsibility for the spill and the harm it caused the fishing and tourism industries.

The 15-square-mile (40-square-km) oil slick spread across the back of the bay and reached Ilha do Governador, the island site of Rio's international airport 12 miles (20 km) from its famous tourist beaches, which have remained out of danger.

But environmentalists say the disaster could have been prevented and blame Petrobras for sloppy management that kept an unlicensed refinery running even after a similar but much smaller spill in 1997.

"Why has Petrobras not taken the steps that it should have, allowing a repetition of the accident, this time with a much bigger spill?" asked Vilmar Berna, editor of the Brazilian environment newspaper Jornal do Meio Ambiente. "The feeling of revulsion mixes with impotence when now faced with the birds with their feathers covered in oil."