Toxic mercury has been found in lakes previously thought to be uncontaminated, state health officials said Tuesday, prompting warnings on consumption of fish from all 10,000 of Michigan's inland lakes.
"Over the past several years seen it showing up in lakes we would not suspect were contaminated," said John Hesse, an environmental scientist for the Public Health Department. "Out of 67 (lakes surveyed), we have 46 showing some mercury above the level of concern. Wisconsin, Minnesota and Ontario are also finding similar levels in their lakes."Studies by the U.S. Environmental Protection Agency and the Michigan Department of Natural Resources showed that fish samples tested last year had mercury levels exceeding 0.5 parts per million, the level that triggers state health advisories.
Previous state mercury warnings had applied to only a handful of Upper Peninsula lakes, where higher water acidity apparently contributes to the problem. But the new samples showed contamination in many Lower Peninsula lake fish.
One sample showed a bass from Lake Orion in Oakland County in southeastern Michigan with mercury contamination of 1.8 parts per million, nearly double the 1 part per million federal standard that must be met for fish sold commercially.
Hesse, who developed the advisory for the state Department of Public Health, said the new warning will be the most sweeping ever issued on inland lakes.
The warning will apply to sport fish that are not sold in stores and restaurants. There is no commercial fishing on inland lakes.
Experts believe mercury is being deposited from the atmosphere because of the burning of coal, incineration of trash, use of latex paints with mercury compounds and other industrial sources.
The advisory, which will be included in the 1989 sport fishing guide, applies to crappies, rock bass and perch more than 9 inches long and to all largemouth and smallmouth bass, walleye, northern pike and muskellunge.
Fish in the affected categories caught in inland lakes should be eaten no more than once a week by those 16 years and older. But it should be eaten no more than once a month by pregnant women, nursing mothers, women who intend to have children and children 15 years and younger, according to the advisory.
Hesse said there have been no reports of mercury poisoning among people who eat Michigan sport fish, and scientific literature suggests no evidence of adverse health effects in people with less than 200 parts per billion of mercury in their blood.
"We have not seen any evidence of mercury poisoning (in the U.S.)," he said. "We want to keep it that way."
Hesse said high doses of mercury affect the central nervous system. Symptoms include a loss of coordination, numbness around the mouth, night blindness, tremors, hearing loss and diminished senses of taste and small.
He said that in the late 1960s, 90 people died of mercury poisoning in Japan.