Federal scientists will test thousands of ocean fish this year to learn whether they contain dangerous levels of mercury that can be passed to people who eat them.
"All the mercury comes from seafood," said LaDon Swann, director of the Mississippi-Alabama Sea Grant Consortium. "There are some species that have more mercury than others."
Mercury can cause neurological problems in adults and developmental problems in babies and children, said Swann, one of three experts who spoke recently at a "Sustainable Fisheries" lecture series at Gulf Coast Research Laboratory. Pregnant women are advised to limit their consumption of fish, and mercury also is suspected to cause heart disease.
The National Marine Fisheries Service plans to test 2,500 fish samples this year to learn whether stricter mercury warnings should be issued. Mercury warnings now exist for king mackerel, shark, swordfish and tilefish.
Mercury enters the marine food chain from the atmosphere and tends to accumulate in large predatory fish, so Swann said people can reduce the threat of mercury poisoning by eating smaller fish.
While federal safety levels are based on averages, people who live near the Coast likely eat much more fish than the national average, said Ben Raines, the environmental reporter for The Mobile Register, who wrote stories last year pointing out that fish high in mercury are sold routinely.
Raines said that more tests are necessary to know which fish contain dangerous levels of mercury.
"The government doesn't know, the scientists don't know and the people eating fish don't know," Raines said.
Wayne Ishpording, a geochemist at the University of South Alabama, said that mercury is one of a host of dangerous heavy metals that industries release into the air and water.
"There are other heavy metals people overlook," he said.
Lead, cadmium, arsenic, thallium and zinc have been found in the sediments of Mobile Bay and the Mississippi Sound. The sources are power plants, shipyards, refineries, fuel spills, industry and runoff.
"We traced a number of metals right back to the discharge points," Ishpording said.
Heavy metals exist in different chemical compositions, some of which are more toxic to humans.
"All metals are carcinogenic in large quantities. Some are carcinogenic in small quantities," he said.
The sediments of Mississippi Sound have a high ratio of the kind of clay and organic materials that absorb heavy metals. High levels of heavy metals have been found in Bayou Casotte in Jackson County, an industrial site. Ishpording's work has also shown that heavily polluted Mobile Bay was cleaned of many toxic metals when Hurricane Frederic scoured the bottom of the bay in 1979.