The journey of mercury — emissions to fish
Date posted: August 30, 2013
SHERIDAN — The world is interconnected. This mantra has been used in recent years to explain how travel, technology and communications have come together to metaphorically shrink the globe. While emailing an acquaintance on the other side of the world in a few seconds seems like a helpful and easy example of this, a less beneficial example of this interconnectedness can be found locally.
Though it may be hard to mentally connect the dots, here it is. The gold ring on your finger and the electricity coursing through a house in China, have likely contributed to the mercury accumulating in the bodies of the fish you catch in Lake DeSmet.
Though mercury in the atmosphere has been tracked for many years by various agencies and governments and many warnings have been issued about safe amounts of seafood people should eat, local data on freshwater fish is more recent.
“They had been collecting data sporadically since the 1970s but it was just one or two fish here and there and we didn’t have a good handle on what was going on,” said Travis Neebling, a fish biologist with the Wyoming Game and Fish Department who has been sampling mercury content of fish in Wyoming waters. “I started looking at it in depth in 2011.”
Through samples of hundreds of fish in dozens of state waters, the study of mercury in fish has expanded. What the findings have shown has encouraged the WGFD and the Wyoming Department of Health to issue fish consumption advisories for various fish species and locations.
“The consumption advice that is available on the Game and Fish website is based on the best available data we have in the past decade,” Neebling explained, adding that due to limited time, money and labor resources, only the most popular lakes and reservoirs are sampled annually, with others sampled on a rotating basis. “We just don’t have the resources to be able to go out and sample every water every year.”
Where it comes from
Neebling said the sources of mercury are varied and include natural and manmade sources.
“There are local sources, coal burning power plants and some mining operations and then some natural leaching out of rocks, but that is pretty small,” Neebling said. “It is a very small amount compared to what is being deposited from the atmosphere.”
“What we are really seeing is atmospheric mercury coming from worldwide sources being deposited,” he continued. “Currently the majority of that global atmospheric mercury is coming out of Asia.”
According to the Global Mercury Assessment 2013 by the United Nations Environment Programme, approximately 62 percent of the annual total anthropogenic (human-caused) mercury air emissions come from artisanal gold mining (about 37 percent) and coal burning (about 24 percent). In addition, it noted that east and southeast Asia are responsible for about 40 percent of global anthropogenic emissions.
The biggest culprit, artisanal or small-scale gold production, is carried out by individuals throughout the world who operate independently without connections to a mining company. Often, chemicals such as mercury are used to bond to small particles of gold in sediment. The bonded gold and mercury is then burned to separate the two elements, releasing mercury into the air.
“It burns off the mercury and leaves them with a nugget of gold and all that mercury ends up in the atmosphere,” Neebling said.
According to the Environmental Protection Agency, 20 percent of the world’s gold is produced by small-scale miners scattered through more than 50 countries.
Once elemental mercury is in the atmosphere, it eventually falls to the Earth’s surface. In a body of water, Neebling said anaerobic bacteria on the lake bottom converts the mercury to methylmercury which is then taken up through the food chain.
“It bioaccumulates and biomagnifies, so larger fish of the same species are going to have a higher load than smaller fish and fish higher on the food chain will have higher levels than fish lower on the chain,” Neebling said. “Our top predators like walleye, brown trout, lake trout, those are species that are typically going to have higher levels of mercury.”
How it’s tested
To test the levels of mercury in fish, biologists take a small tissue sample from the back of a fish. Samples from the same species and similar age and size classes are blended together and sent for testing. The results give an approximate amount of mercury that a person eating that particular species, size and age of fish would be exposed to. Consumption advisories are then created with recommendations for children younger than 15 years of age, women who are pregnant, might become pregnant or are nursing, and all other persons.
For instance, for Lake DeSmet, the advisory suggests up to four meals of 15- to 25-inch walleye per month for children or pregnant women and up to eight meals per month for everyone else.
Consumption advisories are published for waters in many states. However, Neebling said Wyoming is unique in one aspect.
“One of the differences about lakes and reservoirs in Wyoming that makes us particularly susceptible, is a good part of ours are drawn down for irrigation,” he said. “So the mercury is getting deposited directly on the ground and bacteria can begin work on it. So our reservoirs that typically have the higher mercury concentration are ones that are drawn down for a good part of the season like Boysen or Glendo.”
What to do
Neebling emphasized that the recommendations are precautions. The human body is naturally able to excrete some mercury, so keeping intake to a moderate level is the safest course of action.
In addition, the EPA notes on their website that, “the effects of mercury exposure can be very severe, subtle, or may not occur at all…Whether an exposure to mercury will harm a person’s health depends on a number of factors. Almost all people have at least trace amounts of methylmercury in their tissues, reflecting methylmercury’s widespread presence in the environment…”
The EPA noted the risk factors include age and general health of a person, the dose and route of exposure and the duration of exposure.
Neebling said that eating fish is part of a healthy diet and anglers should simply be aware of how much fish and what type of fish they are eating in order to minimize exposure to mercury.
“There’s many positive benefits to consuming fish and a vast majority of the species and size classes that are available to anglers are safe to eat,” he said. “Some of the higher predators and larger class sizes need to be consumed at a lower rate.”
For a complete list of fish consumption advisories, visit wgfd.wyo.gov