03-15-2004, 10:49 PM
Five lakes in S.D. now on mercury warning list
By Kevin Woster, Journal Staff Writer
Five state lakes, including two west of the Missouri River, are now on a state warning list because of elevated mercury levels in fish.
The worrisome list has been growing slowly since April 2000, when officials issued a mercury advisory for walleyes in Bitter Lake in northeastern South Dakota. That was only the state's second advisory for mercury. The first was issued in 1974 for the Cheyenne River and was traced to mining impacts in the Black Hills.
Since the Bitter Lake advisory — in which health officials advised people to limit their consumption of walleyes from the lake — four more lakes have been added to the watch list for mercury levels. The most recent was tiny Roosevelt Lake near Colome in Tripp County.
Mercury has been found in fish taken from other waters, including Lake Oahe on the Missouri River, but not in levels high enough to require advisories.
State Health Department and Game, Fish & Parks officials say the slow growth of the mercury warning list doesn't mean South Dakota waters are increasingly polluted or even that the fish in the listed lakes are unsafe to eat.
"We're not saying quit fishing. We're not saying don't eat fish. We're just saying be informed," GF&P fisheries supervisor Dennis Unkenholz of Pierre said. "To me, the good news is we only have a few lakes on the advisory list. A lot of states couldn't say that."
More than 30 states have issued mercury advisories that offer guidelines for fish consumption. Minnesota, North Dakota, Nebraska and Montana are among them.
Frequently referred to as a heavy metal, mercury is an element that occurs naturally in the environment. But it also is produced by human activities, including coal-fired power plants and gasoline combustion. And it can be released by the improper disposal of manufactured products containing mercury.
Mercury can accumulate in human tissue and damage the nervous system. It is particularly dangerous for children and women who are pregnant or nursing.
In 1984, South Dakota began surveying fish in about 10 lakes each year for heavy metals and other contaminants. Not until Bitter Lake walleyes in 2000 did any fish register at or above 1 part per million (ppm) of mercury, which is the threshold for action established by the federal Food and Drug Administration.
Bitter Lake is a sprawling slough that grew into a 9,000-acre Lake during a wet cycle during the 1990s. It also exploded into a productive fishery for walleyes, northern pike and yellow perch.
State officials never determined a specific source of the mercury levels but theorized that it they might have come from a biological reaction that developed when thousands of acres of vegetation were flooded. In that process, naturally occurring mercury can be converted into methylmercury, a particularly dangerous contaminant that binds with particles and sediments eaten by fish and accumulates in tissues and organs.
As predator fish eat smaller fish, they absorb that mercury. Predator fish such as walleyes, northern pike and bass are more likely to accumulate problem levels of methylmercury.
After mercury levels of 1 ppm were found in Bitter Lake walleyes, subsequent tests confirmed levels of 1.13 in northern pike there. Those fish were added to the advisory, which remains in effect.
In July 2002, the state and Cheyenne River Sioux Tribe issued a mercury advisory for large northern pike in Lake Isabel, an 80-acre lake near the town of Isabel. In November of that year, largemouth bass 17 inches or longer were added to the Lake Isabel advisory.
The next advisory was issued in May 2003 for larger northern pike and walleyes in Twin Lakes in Kingsbury County. That was followed in August by an advisory for larger largemouth bass in Lake Hurley in Potter County.
The Roosevelt Lake advisory was issued Feb. 24 for largemouth bass 18 inches and longer. Bigger, older fish tend to have more exposure to mercury and accumulate more of the contaminant in their flesh.
Dave Micklos, a spokesman for the state Health Department in Pierre, said people shouldn't overreact to the mercury advisories. But the scattered nature of the listed lakes shows that mercury can have widespread impacts, he said.
"People need to realize this mercury problem isn't exclusive to northeastern South Dakota," he said. "It can happen anywhere. We're on the watch for it. And when we find it, we'll sure let people know."
GF&P crews have sampled fish in Black Hills area lakes and streams without finding problem mercury levels, Micklos said.
"Nothing has shown up in the Hills," he said. "We weren't expecting to find it down in Tripp County. But there it was."
It's not clear why the problem developed at Roosevelt Lake, a 65-acre lake southeast of Colome. Some soil types are more likely to produce mercury, which might be the simple answer at Roosevelt, Unkenholz said.
Although Game, Fish & Parks Department fisheries crews take fish samples from pre-determined lakes each year, those lakes that have tested at 1 ppm are retested regularly to monitor levels.
Meanwhile, consumption guidelines at those lakes recommend that healthy adults eat no more than 7 ounces a week of fish listed on the advisory. Children younger than 7 years old should eat no more than 4 ounces a month. And women who are breast-feeding, pregnant or planning to become pregnant should eat no more than 7 ounces a month.
Seven ounces of fish is about the size of two decks of playing cards.
Micklos said he believes the 1 ppm-advisory threshold and the consumption recommendations are reasonable responses to the mercury problem in some lakes.
"I think that's a safe level," he said.
Unkenholz said fish are still a nutritious and generally healthy food option for people. But limiting consumption in affected waters only makes sense, he said.
And the fact that more than 80 lakes have been tested with only five showing up with problem fish is good news, Unkenholz said.
"I don't think we need to alarm people," he said. "We just want people to be smart. And remember there's a high number of lakes in South Dakota where you don't have to worry about it."
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By Kevin Woster, Journal Staff Writer
Five state lakes, including two west of the Missouri River, are now on a state warning list because of elevated mercury levels in fish.
The worrisome list has been growing slowly since April 2000, when officials issued a mercury advisory for walleyes in Bitter Lake in northeastern South Dakota. That was only the state's second advisory for mercury. The first was issued in 1974 for the Cheyenne River and was traced to mining impacts in the Black Hills.
Since the Bitter Lake advisory — in which health officials advised people to limit their consumption of walleyes from the lake — four more lakes have been added to the watch list for mercury levels. The most recent was tiny Roosevelt Lake near Colome in Tripp County.
Mercury has been found in fish taken from other waters, including Lake Oahe on the Missouri River, but not in levels high enough to require advisories.
State Health Department and Game, Fish & Parks officials say the slow growth of the mercury warning list doesn't mean South Dakota waters are increasingly polluted or even that the fish in the listed lakes are unsafe to eat.
"We're not saying quit fishing. We're not saying don't eat fish. We're just saying be informed," GF&P fisheries supervisor Dennis Unkenholz of Pierre said. "To me, the good news is we only have a few lakes on the advisory list. A lot of states couldn't say that."
More than 30 states have issued mercury advisories that offer guidelines for fish consumption. Minnesota, North Dakota, Nebraska and Montana are among them.
Frequently referred to as a heavy metal, mercury is an element that occurs naturally in the environment. But it also is produced by human activities, including coal-fired power plants and gasoline combustion. And it can be released by the improper disposal of manufactured products containing mercury.
Mercury can accumulate in human tissue and damage the nervous system. It is particularly dangerous for children and women who are pregnant or nursing.
In 1984, South Dakota began surveying fish in about 10 lakes each year for heavy metals and other contaminants. Not until Bitter Lake walleyes in 2000 did any fish register at or above 1 part per million (ppm) of mercury, which is the threshold for action established by the federal Food and Drug Administration.
Bitter Lake is a sprawling slough that grew into a 9,000-acre Lake during a wet cycle during the 1990s. It also exploded into a productive fishery for walleyes, northern pike and yellow perch.
State officials never determined a specific source of the mercury levels but theorized that it they might have come from a biological reaction that developed when thousands of acres of vegetation were flooded. In that process, naturally occurring mercury can be converted into methylmercury, a particularly dangerous contaminant that binds with particles and sediments eaten by fish and accumulates in tissues and organs.
As predator fish eat smaller fish, they absorb that mercury. Predator fish such as walleyes, northern pike and bass are more likely to accumulate problem levels of methylmercury.
After mercury levels of 1 ppm were found in Bitter Lake walleyes, subsequent tests confirmed levels of 1.13 in northern pike there. Those fish were added to the advisory, which remains in effect.
In July 2002, the state and Cheyenne River Sioux Tribe issued a mercury advisory for large northern pike in Lake Isabel, an 80-acre lake near the town of Isabel. In November of that year, largemouth bass 17 inches or longer were added to the Lake Isabel advisory.
The next advisory was issued in May 2003 for larger northern pike and walleyes in Twin Lakes in Kingsbury County. That was followed in August by an advisory for larger largemouth bass in Lake Hurley in Potter County.
The Roosevelt Lake advisory was issued Feb. 24 for largemouth bass 18 inches and longer. Bigger, older fish tend to have more exposure to mercury and accumulate more of the contaminant in their flesh.
Dave Micklos, a spokesman for the state Health Department in Pierre, said people shouldn't overreact to the mercury advisories. But the scattered nature of the listed lakes shows that mercury can have widespread impacts, he said.
"People need to realize this mercury problem isn't exclusive to northeastern South Dakota," he said. "It can happen anywhere. We're on the watch for it. And when we find it, we'll sure let people know."
GF&P crews have sampled fish in Black Hills area lakes and streams without finding problem mercury levels, Micklos said.
"Nothing has shown up in the Hills," he said. "We weren't expecting to find it down in Tripp County. But there it was."
It's not clear why the problem developed at Roosevelt Lake, a 65-acre lake southeast of Colome. Some soil types are more likely to produce mercury, which might be the simple answer at Roosevelt, Unkenholz said.
Although Game, Fish & Parks Department fisheries crews take fish samples from pre-determined lakes each year, those lakes that have tested at 1 ppm are retested regularly to monitor levels.
Meanwhile, consumption guidelines at those lakes recommend that healthy adults eat no more than 7 ounces a week of fish listed on the advisory. Children younger than 7 years old should eat no more than 4 ounces a month. And women who are breast-feeding, pregnant or planning to become pregnant should eat no more than 7 ounces a month.
Seven ounces of fish is about the size of two decks of playing cards.
Micklos said he believes the 1 ppm-advisory threshold and the consumption recommendations are reasonable responses to the mercury problem in some lakes.
"I think that's a safe level," he said.
Unkenholz said fish are still a nutritious and generally healthy food option for people. But limiting consumption in affected waters only makes sense, he said.
And the fact that more than 80 lakes have been tested with only five showing up with problem fish is good news, Unkenholz said.
"I don't think we need to alarm people," he said. "We just want people to be smart. And remember there's a high number of lakes in South Dakota where you don't have to worry about it."
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