A first-of-its-kind scientific study has determined that the dispersant BP sprayed at the oil gushing from the Deepwater Horizon rig in 2010 harmed human health. The symptoms — coughing, wheezing, skin irritations and burning eyes — tended to last only a little while for most of the people who were cleaning up the spill, said Dr. Dale Sandler, who's leading the study for the National Institutes of Health. But not for all of them, she said. Some people in the study were still experiencing those symptoms, she said. And some did not develop those symptoms until well after the disaster had ended, she said. "We need to do a lot more research on this" to determine if there are long-term health effects, Sandler said in an interview Friday. The NIH study is the first to look at human health impacts of using dispersants to break up oil spills, a common oil industry approach to dealing with such disasters. With Deepwater Horizon, BP sprayed nearly 2 million gallons of a dispersant called Corexit, both on top of the water and down near the floor of the Gulf of Mexico. TAMPA BAY TIMES COVERAGE: 2010 DEEPWATER HORIZON OIL SPILL Deepwater Horizon oil, dispersant toxic to coral in Keys (Jan. 9, 2013) Divers say they still suffer ailments from 2010 BP oil spill (May 26, 2013) Study finds high incidence of respiratory problems in oil spill cleanup workers (April 17, 2015) About 600 of the thousands of people hired to help clean up the oil were exposed to the dispersants, the study determined. They were the ones out on the water in boats or in diving suits, chasing oil slicks or collecting samples from underwater — not the people in hazmat suits walking the beaches. Sandler said the study did not divide up the 600 by which states they were from, but some of the on-the-water work was being done by Florida shrimpers, divers and commercial fishermen. The Deepwater Horizon disaster started on April 20, 2010, when the oil rig 150 miles off the Louisiana coast exploded, killing 11 people. The rig sank, and two days later oil began gushing from 5,000 feet below the Gulf of Mexico's surface. Oil washed up on the coasts of Louisiana, Mississippi, Alabama and, in June, finally reached Florida. Thousands of shiny, reddish-brown globs, some as big as Frisbees, tainted the sugar-white beaches across eight Florida counties, while tar mats the size of throw rugs floated just offshore. BP was unable to shut off the flow from the submerged rig until July, which meant an estimated 4.9 million barrels of oil had spewed out and spread through the gulf. Some of it settled on the ocean floor and some was consumed by oil-eating bacteria. But plenty of it washed ashore — including, four years after the disaster, a 1,000-pound mat that showed up near Pensacola Beach. To try to prevent the oil from washing ashore and fouling beaches, Environmental Protection Agency Administrator Lisa P. Jackson approved BP's use of chemicals known as dispersants, which are supposed to break up the oil into tiny droplets that can be easily consumed by bacteria. The EPA had tested Corexit on fish and shrimp before clearing it for use, Jackson said, declaring it safe. With EPA permssion, BP sprayed the dispersant directly at the wellhead spewing oil, something no one had ever tried before. BP also used more of the dispersant than had been used in any previous oil spill, 1.8 million gallons. Subsequent studies have determined that the mixture of Corexit and oil was toxic to marine organisms, including corals. But the human health impacts were a mystery. In the past 50 years, in 40 known oil spills around the world, only eight have been studied for human health impacts. Those studies found that cleanup workers exposed to crude oil often suffer acute short-term effects — stinging eyes, rashes, nausea, dizziness, headaches, coughs and other respiratory symptoms. But there have been no studies of the long-term health effects. So in February 2011, the National Institute of Health announced that it would spend a decade studying the health impact on the 33,000 cleanup workers who tackled the 2010 oil spill — the largest such study in the agency's history. Those workers would walk the beaches in the sun for 10 minutes, then sit in the shade for 50, or put in 14 hours at night when no one saw them. They wore hard hats and steel-toed boots as they trudged along the beach scooping up tar balls. Meanwhile there were divers, boaters and anglers out on the water, most of them forming a makeshift armada trying to intercept the oil before it could get to shore. Later, they began reporting feeling sick. One Louisiana-based diver, after plunging 80 feet deep into the gulf, told the Times in a 2013 interview that he saw 6-foot-long "mucus-like strands of what appeared to be oil that was not completely dispersed." After he came back to shore, he said his chest burned, his head pounded and he couldn't stray far from a restroom. Representatives of BP and Nalco, which manufactures Corexit, did not return requests for comment. In 2013, in response to the divers' complaints, BP spokesman Jason Ryan said the company "is not aware of any data showing worker or public exposures to dispersants at levels that would pose a health or safety concern." Times senior news researcher Caryn Baird contributed to this story. Contact Craig Pittman at [email protected] Follow @craigtimes.