News Coverage
Heed state's mercury warnings
Fish in many La. waters may be dangerous to eat
Published March 29, 2004
Ever since the 1950s when residents living near a chemical plant in Minimata, Japan, began showing signs of mercury poisoning -- weakening muscles, tingling hands and feet, hearing loss, slurred speech, a trembling walk and brain damage -- scientists have tuned into the effects mercury has on populations where fish is a staple in their diet.
What happened in Minimata was the result of a plant discharging wastewater containing mercury compounds into area waters. Though mercury and its compounds occur naturally, the wastewater contributed to abnormally high mercury levels found in the fish. The compounds were absorbed by critters on the low end of the food chain. As big fish ate little fish, the mercury was passed along into the tissues of predators until humans made fish a meal.
Mercury is the world's only liquid metal, and not usually absorbed. But in its methylated form -- when bacteria breaks down compounds like mercuric sulfide, mercuric sulfate and mercuric chloride-- it is readily ingested by fish and other aquatic animals.
While the water some fish live in has traces of mercury, the fish can absorb mercury in concentrations as high as one million times the amount of mercury present in the water. Scientists call this process "biomagnification."
That's why the Louisiana Department of Environmental Quality has updated warnings through the years. The DEQ's 2003 Annual Mercury Report cites a U.S. Environmental Protection Agency report, "Scientists have learned that dietary intake of mercury is the most prominent route of (human) exposure, as dietary methyl mercury is almost completely absorbed by the body."
Usually the larger the fish, the greater the chance it has mercury levels that call for a warning. Women of childbearing age, women breast-feeding their children and children younger than seven years old are hardest hit by eating fish tainted by mercury. Other adults and older children fall into another less restrictive consumption warning.
The warnings aren't confined to small streams and backwater areas.
Places including Toledo Bend Reservoir, Calcasieu River, Vernon Lake, some Florida Parishes rivers and streams, Bayou De Saird, Lake Larto, the new Grand Bayou Reservoir, Blind River and Henderson Lake are on the advisory list.
Many freshwater species are on the list for at least one waterbody.
Saltwater fishermen need to heed the warnings, too. King mackerel is the main target of the advisories and, to a lesser degree, so are shark, swordfish and tilefish.
The DEQ's full 2003 report can be found on its Web site: www.deq.state.la.us/surveillance/mercury/2003-mercury-report.pdf.