Birds, sea turtles, fish and other species are more likely to be harmed by an aggressive cleanup than by simply leaving remnants of oil and letting it slowly degrade, the Coast Guard said.
The report was designed to guide the cleanup of the BP PLC spill from the April 20 Deepwater Horizon rig explosion. There are 4,265 people still involved in the cleanup and response on 544 miles of coast.
Recent oil samples show weathered oil found along beaches has lost the majority of the toxic compounds in it and the oil left on shores meets federal safety thresholds for people, the Coast Guard said.
At least one researcher questioned the Coast Guard's report.
Wilma Subra, a Louisiana chemist and consultant for environmental groups, said the toxic elements could last for decades and warned the report could let BP abandon cleanup before its complete.
"The real concern is if they walk away and it's not clean enough," said Subra, who has been doing her own testing along the coast. If it's not clean enough, people and animals could still be exposed to harmful toxins, she said.
The study focused on beaches in Grand Isle, La., Petit Bois Island, Miss., Bon Secour, Ala., and Fort Pickens, Fla.
"Beach cleanup is invasive," said Lt. Cmdr. Kenneth Boda of the Coast Guard. "If we were to go in and remove the small bit of oil you'd have to wash the sand, and you'd kill everything else in there."
He said that could include removing plants, shells and other sources of food for birds, as well as damaging sea turtle eggs.
"We can sterilize the sand, but then there aren't any nutrients left," said Edward H. Owens, a cleanup technical adviser for BP. "Just cleaning and sterilizing is not necessarily in the short term of high value."
Since the spill, BP has been cleaning up oil and teams have established guidelines to determine what is clean enough. The cleanup varies from beach to beach. For example, recreational and manmade beaches are getting washed and cleaned much more thoroughly than sand abundant in wildlife and plants.
The report signaled the cleanup was nearing an end.
BP has cleanup crews on the Gulf Coast and they will stay around to clean up when oil shows up on shores, Owens said. Oil remains buried in sand and as submerged mats along the coast and still washes ashore occasionally.
"We're finding in some isolated places new oil because it was buried," Owens said. "We're getting down to a smaller length of shoreline that has to be cleaned up and smaller amounts of oil."