The mental health impacts of the BP oil spill will dwarf those encountered after the last major oil spill off US shores, a sociologist who studied the Exxon Valdez spill told Florida volunteers.

University of South Alabama researcher Steve Picou said the effects of the spill will far overshadow the negative effects experienced by 30,000 Alaska residents after the Exxon tanker dumped millions of gallons (litres) of crude into Prince William Sound in 1989.

Twenty years after that disaster, a "significant minority" of those residents continue to suffer the mental health consequences and Picou said the BP Plc spill will affect far more people in communities along the Gulf of Mexico.

"What we're looking at here ... it boggles my mind," Picou said. "Because you're talking about hundreds and hundreds of communities and you're talking about millions of people."

The economic and ecological costs to tourism, wildlife, fishing and other industries continue to mount for four states along the US Gulf coast after Deepwater Horizon drilling rig sunk in 5,000 feet (1,524 metres) of water on April 22, two days after an explosion and fire killed 11 workers.

Louisiana officials on Monday asked BP to pay $10 million to help provide mental health services, the second time the state has requested funds to pay for counseling and other psychological services.

Unlike a natural disaster, which generally has a definable beginning and an end, the BP spill is ongoing after 71 days and most of the effects will remain unknown for some time, Picou told Florida volunteers. Such an extended period of uncertainty leads to depression, marital discord and substance abuse as people isolate themselves from other members of the community.

Damages unfolding

"The important point is that no one can be rescued because it continues," Picou said. "You cannot take an inventory of damages because the damages are unfolding."

While the hotel business isn't horrible, the frenetic pace that usually begins Memorial Day weekend and continues through August is noticeably absent in the Florida Panhandle beach communities.

Charter boat operators and commercial fishermen have been more immediately affected, their livelihoods having been idled by the oil spewing from the blown well more than 100 miles (160 km) away.

Food stamp applications are up nearly 20 per cent in the past 60 days along the Panhandle region. Unemployment is also up in the region, surpassing a statewide rate of nearly 12 per cent.

Florida social services officials say they are already seeing increases in domestic abuse, child neglect and the other social maladies that come when money is tight and the future unclear.

"These people are scared, they're worried, they're frustrated," Phil Wieczynski, a Florida environmental official, said after a recent visit with 400 residents from the coastal city of Port St. Joe.

"They see what's going on and we need to do whatever we can to assure them that steps are going to be taken to address issues and protect their way of life."

Volunteers were urged on Tuesday to coordinate their activities to be able to successfully respond to long-term effects.

"This is going to burn out any individual group," said Doug Zimmerman, president and CEO of VisionLink, a company that offers software for disaster recovery and volunteer management. – Reuters