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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Jim Amrhein prepares a bass for mercury sampling. © Robert Queen

June 2001

Limiting the hitch in the day's catch

It's easier than ever to minimize the risk of mercury exposure from eating sport fish. The bad news? Mercury remains a metal on the move that is more widespread than we realized.

Jennifer Pelej


Jim Amrhein prepares a bass for mercury sampling.

© Robert Queen

The science behind the advisory | Where does mercury come from?
Dispelling mercury myths and fears
Another fine reason not to eat loons
What about fish from restaurants and grocery stores?

Inside the walls of the State Lab of Hygiene, it's an eclectic assortment of rubber boots, white lab coats, fish guts and country music. At this office "getaway," Jim Amrhein, DNR fish contaminant specialist, performs his studies on Wisconsin fish. Like most anglers, he'd rather be catching tonight's supper instead of working, but Amrhein's proud of his role in protecting the health of Wisconsin's visitors and residents for the past 16 years.

Long-term studies by the Department of Natural Resources, the Division of Health and the State Lab on mercury levels in fish led to changes in the advice that Amrhein and his colleagues offer people about eating sport fish during the 2001 fishing season. First, the annual fish advisories now cover all Wisconsin inland lakes and rivers. Second, the guidelines on consuming fish are much easier to interpret.

Mercury levels haven't changed much in fish. In fact, levels have remained remarkably constant in waters where fish are sampled.

"What's changed is we're learning that mercury is more widespread in the environment, and we're concerned about exposure to smaller amounts of this contaminant," Amrhein explained. Fetuses and young children are especially susceptible to neurological changes and possible learning disabilities from continued exposure to even the small amounts of mercury in sport fish.

Our aim is giving people reasonable guidelines to continue enjoying the many benefits of eating fish while minimizing health risks throughout their lifetime, said Dr. Henry A. Anderson, chief medical officer for the Wisconsin Division of Public Health. To reduce mercury exposure, it's time to get a little more cautious by spreading out the number of meals of fish eaten during a week or month, particularly for pregnant women and young children, Anderson said.

"It's not a 'don't eat fish' advisory, but instead a guideline on how much to eat,"said Amrhein.

The mercury guidelines this year suggest that:

  • Women of childbearing years, nursing mothers and children younger than 15 eat only one meal per week of panfish, such as bluegill and perch, and one meal per month of predator species like walleye, northern, bass, catfish and bottom feeders like carp.
  • Women beyond their childbearing years and men may eat unlimited amounts of panfish and one meal per week of large predator fish mentioned above.

The science behind the advisory

In the past, mercury advisory levels were set one lake at a time following fish sampling by DNR, analysis by the State Lab and interpretation by the Division of Health.

Each year Amrhein sends fish managers a list of lakes that will be sampled. Using fyke nets or boom shockers, fisheries crews collect about 10 top-level fish, such as walleye and northern pike, of varying sizes from each lake on the list. It's safe to assume that if predators have low levels of mercury than other fish down the food chain, like panfish, will also have low levels.

The collected fish are frozen and shipped on ice to Madison. What looks like the preparation for a Friday night fish fry is actually the beginning of the contaminant research. Each fish is thawed and filleted.

Amrhein also records the sex of each fish, examines its stomach contents and includes the information in notes about each sample. Since mercury accumulates up the food chain, there is a direct correlation between what the fish eats and its mercury level. Unlike the contaminant PCB (polychlorinated biphenyl), mercury is stored in muscle. You can't trim away the skin and fatty portions of fish to reduce mercury concentrations.

An atomic absorption spectophotometer is used to detect minute amounts of mercury in fish. © Robert Queen
An atomic absorption spectophotometer is used to detect
minute amounts of mercury in fish. © Robert Queen

"Since the studies are done to conclude how much fish a person can safely eat, we fillet each fish as if it was going to be eaten," Amrhein said. "The idea that we use the whole fish to test for fish contaminants is a huge myth. We only test edible skin-on fillets for signs of mercury."

Next, instead of battering and frying the fillet, Amrhein feeds the fillets into a meat grinder until the fish sample is well blended and the consistency of ground hamburger. Ground samples are sealed in a container, frozen, and sent to the lab where other scientists read the mercury levels using a high-tech computerized machine called an atomic absorption spectrophotometer.

"This testing process is unbelievably methodical," Amrhein said. "We go through a lot of steps in order to get consistent, reliable analyses." About $200,000 is spent each year collecting fish, preparing samples and analyzing them for signs of mercury, PCBs, dioxins and pesticides. Federal grants and the general state tax funds pay for that testing.

Where does mercury come from?

Research during the last 20 years has started to piece together a picture of how the contaminant spreads through the environment. Mercury is a naturally occurring element, released when volcanoes erupt, when rocks erode and when fossil fuels are burned. Manmade sources in Wisconsin include a chlor-alkali factory, power utilities, home heating fuels, waste incinerators, fluorescent lights, mercury electrical switches and home appliances that contain mercury.

What about fish from restaurants and grocery stores?
Restaurants and grocery stores sell fish that is commercially raised in fish farms or commercially netted from rivers and the ocean. Some kinds of ocean fish have mercury levels on a par with walleyes, northerns and bass. Other species have even higher mercury levels. In fact, the U.S. Food and Drug Administration (FDA) has warned pregnant and nursing women not to eat shark, swordfish, king mackerel and tilefish because they contain higher levels of mercury (above one part per million).

On the other hand, ocean species that are the staple of Friday night fish fries – cod, ocean perch and haddock – are relatively lower in mercury, on a par with our panfish. These fish are unlikely to concentrate as much mercury because natural conditions in the oceans are less conducive to forming methylmercury that moves through food chains.

Farm-raised fish are also less likely to accumulate mercury unless the controlled pellet diet they receive contains high levels of mercury.

Commercially raised and harvested fish are inspected and regulated by the FDA News accounts suggest that bacterial contamination in handling fresh fish and moving them to market is a larger issue for commercial fish than mercury contamination.

The main source of mercury in the water is actually the air. Fine particles of mercury released from coal-fired power plants and other sources drift in the air, attach to fine water droplets and fall into lakes and rivers. The particles are so light that they can travel across several states before rain and snow wash them from the sky onto land and into lakes, rivers and streams. Some of the emissions falling in Wisconsin come from sources within the state, some from regional emissions; just as some of our emissions drift to other states and provinces.

Not all waters are equally susceptible to the damaging effects of mercury. In shallower waters with soft bottoms that become depleted of oxygen, mercury particles settle and are digested by bacteria that thrive in these low-oxygen conditions (anoxia). The mercury is converted to methylmercury that moves more readily into tiny plants and animals that fish feed on. It's this form of methylmercury that accumulates in food chains, fish and people.

Mercury is much more of a concern in inland lakes because the Great Lakes don't develop a low-oxygen zone near the lakebed and don't contain large numbers of anoxic bacteria. So the majority of mercury that falls in the Great Lakes is not converted to a form that would move through food chains. The same holds for ocean water. The oceans don't contain as many of the bacteria that could readily convert mercury into a form that is easily absorbed by living organisms.

"There has always been a small amount of mercury entering waterbodies and fish," Amrhein said, "but we're concerned that manmade sources add more mercury more quickly to the environment."

Under the Clean Air Act, utilities are required to meet standards to reduce the risks of inhaling mercury, but the act doesn't address the problem of mercury deposition on lakes. In response, DNR staff is drafting a rule to reduce mercury air emissions that will be presented to the Natural Resources Board this summer.

Dispelling mercury myths and fears

Amrhein is the first to see how mercury can accumulate in fish. So how come he is not afraid to catch and eat them? He knows the nutritional benefits of eating fish outweigh the risks when the guidelines are followed.

"When people put into perspective how much fish they eat per year, they will realize they probably don't have much to worry about," Amrhein said. "Most people already follow the advice without trying."

Eating a meal a week of panfish or a meal a month of game fish gives mercury a chance to get out of the body. Unlike PCBs, which accumulate over a lifetime, mercury is water-soluble and half the amount ingested will be expelled from the body within 70 days. Amrhein calls it the "everything in moderation advice." If fish are eaten in moderation, mercury in the blood will not reach harmful levels.

"Most of us know from our upbringing that too much of anything can be harmful," Amrhein said. Since 1971, DNR and the Division of Health have partnered to offer the angling public advise on which fish could be eaten freely, which should be eaten in moderation and which should be avoided to reduce the risks of the environmental contaminants mercury and PCBs. Even though updated advisories were produced and publicized every year, "we want to create awareness, but we don't want people to misinterpret the advice and stop eating fish," Amrhein said.

Although Wisconsin took greater efforts than other states did to alert its anglers, only a third of people in angling households, and fewer immigrants knew about the advisory. Clearly, the annual publicity wasn't enough and the information was difficult to interpret for many people.

Now, the Department of Natural Resources has partnered with the Division of Health to create a campaign called "Hook Into Healthy Fish." Funded by grant money, the campaign aims to promote awareness of mercury issues without creating undue alarm.

The DNR is taking the "Hook Into Healthy Fish" campaign to Women, Infant and Children (WIC) groups, minority groups, especially those that don't speak English as their primary language, tribes, and angling associations. Instead of just relying on information in written advisories, the healthy fishing message will be printed on coffee cups, T-shirts, posters, magnets, perhaps children's sippy cups, bibs and other props. It is hoped that the promotional items will make their way into doctors' offices so people can get advice from their physician in addition to contacting the Department of Natural Resources.

The team also plans to work with the Great Lakes Indian Fish and Wildlife Commission, tourism outlets, electric utilities, fishing guides, physicians and health maintenance organizations to spread the word wider about the simpler health advice for the fish-eating public.

One partner, Richard "Moose" Speros, secretary of the Wisconsin Department of Tourism, has already commended the streamlined approach for being honest and straightforward.

"That's quite an endorsement given that Mr. Speros is not only the head of tourism, but owns and operates a resort and is a lifelong angler," Amrhein said. "We understand, as he does, that discriminating anglers want advice on which fish in their catch are safest to keep and eat."

The DNR also published a revised advisory booklet this spring that included the new guidelines about mercury in fish and continued PCB advisories that are still listed for individual waters that have been tested. These booklets can be picked up at DNR service centers and ranger stations. All of the information is also listed at Department of Natural Resources.

Jennifer Pelej is a DNR Communications Specialist and fishing enthusiast based in Madison.

Another fine reason not to eat loons
Loons, of course, are a protected species, are not eaten by people, and are a true joy to watch on the water. According to DNR mercury researcher Mike Meyer, loons may also be the ideal animals to study to measure the spread of mercury through animal food chains. Loons accumulate more mercury than most fish or other animals for several reasons:

  • Loons solely eat fish, and lots of it. Meyer estimates that a loon family of two adults and two chicks can pound down about 1,200 perch and bluegills a year. If panfish have been accumulating mercury, researchers will certainly find signs of it in loons.

  • Loons live for 20-25 years and may be exposed to low levels of mercury in their food over a long period of time.

  • Of the fish-eating animals like mink, eagles, osprey, otters and others, loons eat more fish over a longer period of time. The other animals eat a wider variety of foods that may include carrion, plants and insects.

  • Loons choose to nest on the same kinds of lakes where mercury is most likely to be converted to methylmercury that accumulates in food chains – lakes with vegetation and shallower bottoms and bays.

  • Loons are easy to test for signs of mercury contamination. Mercury levels can be measured by drawing blood and feather samples.

  • Loons stay together in family groups. They return to the same territories each year and their behavior can be watched by researchers during the day.