Mercury discoveries
Six out of 10 lakes in southwest Oklahoma have been tagged with consumption advisories by the State Department of Environmental Quality because of mercury levels discovered in fish. The DEQ cleared four other area lakes in the agency’s latest round of testing. Two of Lawton’s sources of drinking water, lakes Ellsworth and Lawtonka, were not labeled with a mercury advisory. A third, Waurika Lake, was.
Other lakes and reservoirs in southwest Oklahoma receiving a mercury advisory were Frederick, Tom Steed, Quanah Parker, Elmer Thomas, and Rush (just west of Medicine Park). Fort Cobb, Foss, Ellsworth and Lawtonka lakes passed the test. In all, 92 Oklahoma lakes were tested. The results prompted the DEQ to place consumption warnings on 63 lakes because of their mercury levels. The amount of mercury in a lake does not affect the reservoir’s safety as a source of drinking water or for recreation such as swimming or boating, the DEQ reports.
GUIDELINES FOR ‘GENERAL,’ ‘SENSITIVE’ POPULATIONS
The DEQ guidelines contain advice for the “general population” and for individuals who are in a “sensitive population.” The sensitive population is defined as children up to age 15 and women of childbearing age (15-45). The general population is men older than 15 and women older than 45. Meal size is 8 ounces, with the assumption that younger children will eat smaller meals.
• The guidelines for Rush Lake contain warnings about consumption of largemouth bass.
No restriction is advised for the general population nor for consumption of largemouth bass shorter than 11 inches caught in Rush Lake. But, people in the sensitive category are advised to limit consumption of largemouth bass from Rush Lake to two meals per month if the fish are 11 inches or longer. Species from Rush Lake tested and found to be safe for consumption include bluegill sunfish, black crappie, green sunfish and redear sunfish.
• At Elmer Thomas Lake, which straddles the Wichita Mountains Wildlife Refuge and Fort Sill Army Reservation, the DEQ recommends members of the sensitive population limit consumption of largemouth bass of any length whatsoever to just two meals per month.
Species from Elmer Thomas Lake tested and found to be safe for consumption include bluegill sunfish, channel catfish, green sunfish, and redear sunfish.
• Quanah Parker Lake has advisories regarding consumption of black crappie, largemouth bass, and warmouth sunfish.
• Consumption recommendations for Lake Frederick included blue catfish, flathead catfish, largemouth bass, white bass and white crappie.
Particular guidelines pertaining to consumption of fish from each lake are available online at go.usa.gov/xdBCV. More detailed information about each lake’s fish consumption guidelines can be received by calling 866-412- 3057 or emailing fishadvisory @deq.ok.gov.
MERCURY ACCUMULATES ‘AS IT WORKS ITS WAY UP THE FOOD CHAIN’
The DEQ promotes fishing and encourages Oklahomans to “enjoy eating the fish they catch.” However, the agency advises, “Just keep in mind that not all fish should be eaten in unlimited amounts.” Some fish pose a higher risk of mercury contamination. “Once mercury gets into a water body, it has to be converted to a biological form to enter the food chain,” Jay Wright of the DEQ explained. “Concentrations of mercury in the water are so low, they cannot be measured in the DEQ lab,” he said.
“But it bioaccumulates as it works its way up the food chain.” Bacteria in the water make the bioconversion into a form called methylmercury, which is absorbed by tiny aquatic organisms. “Those get eaten by small bugs, and those get eaten by small fish, and in turn those get eaten by bigger fish, etc.,” Wright said. The process is why predator fish such as largemouth bass have higher mercury values than do crappie and catfish, he said. And among “bottom feeders,” channel catfish and blue catfish have lower values than flathead catfish, Wright said.
MYRIAD SOURCES OF MERCURY
Mercury contamination is global and affects many waters that have no obvious source of the heavy metal. The element is released into the atmosphere via man-made processes (mining, coal-fired power plants, waste incineration, manufacturing, and other industries), and by natural processes (volcanoes, geothermal springs, and the weathering of geologic deposits), said DEQ Communications Director Erin Hatfield.
“It then falls out of the air by sticking to dust particles, or gets washed out by rain or snow, then runs off into streams and lakes,” she said. Mercury sources can be local, national or global, she added. Mercury is most notable for its neurological effects. In general, the U.S. Food and Drug Administration warns too much mercury can cause anxiety, depression, irritability, memory loss, numbness, and pathologic shyness. While DEQ still monitors fish at some legacy sites for chlorinated pesticides, in 2007 the agency began focusing on mercury levels in fish from Oklahoma’s lakes. The DEQ says it monitors the presence of mercury in fish throughout the state on a rotating basis. The last DEQ mercury advisory was issued in 2017.