Mercury in Fish: Natural or Contamination?

[Newbie1]

How did fish end up having mercury on them?. Is it natural to them?. Does the meat side of the fish also contain mercury or just the skin side?.

 

[alxm]

Fish and other animals shouldn't have mercury in them, because normally there isn't much free mercury moving around in the ecosystem.

The problem with mercury is, in addition to being toxic and essentially indestructible, is that it bio-accumulates. Which means that it gets more concentrated as it moves up the food chain. You have a little mercury in the water, and you get algae with a little mercury in it, which gets eaten in large quantities by some tiny critters, who then get a higher concentration of mercury in them. Those critters then get eaten in large quantities by fish, who get eaten by other fish, who get eaten by people, and the mercury moves upwards.

It tends to accumulate in the fatty tissue (fat). So it's really all throughout the fish, and it's worse in fatty fish like herring.

 

[Newbie1]

Fish and other animals shouldn't have mercury in them, because normally there isn't much free mercury moving around in the ecosystem.

The problem with mercury is, in addition to being toxic and essentially indestructible, is that it bio-accumulates. Which means that it gets more concentrated as it moves up the food chain. You have a little mercury in the water, and you get algae with a little mercury in it, which gets eaten in large quantities by some tiny critters, who then get a higher concentration of mercury in them. Those critters then get eaten in large quantities by fish, who get eaten by other fish, who get eaten by people, and the mercury moves upwards.

It tends to accumulate in the fatty tissue (fat). So it's really all throughout the fish, and it's worse in fatty fish like herring.

So how did the mercury ended up in the water?.

 

[alxm]

So how did the mercury ended up in the water?.

Pollution, usually. Which is why mercury is essentially banned everywhere now.
Great pains are taken to make sure it doesn't end up in nature.

 

[Astronuc]

Here are some discussions on mercury.

Fact Sheet on Mercury Pollution from Coal-Fired Power Plants in Kansas
http://kansas.sierraclub.org/Wind/Coal-MercuryFactSheet.htm

Coal fired power plants are currently the largest single source of airborne mercury emissions in the United States. Airborne mercury emissions travel tens to hundreds of miles before depositing, primarily in rainfall, into lakes and streams where it accumulates in fish that may be eaten by people. This adds to uptake via seafood consumption. The EPA recently announced that 1 in 6 women of childbearing age in the US have blood mercury levels that could be harmful to a fetus. Fish mercury levels in Kansas lakes have been increasing.
. . . .

http://www.fossil.energy.gov/programs/powersystems/pollutioncontrols/overview_mercurycontrols.html

Trace amounts of mercury can exist in coal and other fossil fuels. When these fuels burn, mercury vapor can be released to the atmosphere where it may drift for a year or more, spreading with air currents over vast regions of the globe. In 1995, an estimated 5,500 tons of mercury was emitted globally from both natural and human sources. Coal-fired power plants in the United States contributed less than 1 percent of the total.
. . . .

http://www.epa.gov/mercury/


Mercury Emissions Up at Coal-Burning Power Plants
http://www.ens-newswire.com/ens/nov2008/2008-11-21-092.asp

WASHINGTON, DC, November 21, 2008 (ENS) - The top 50 most-polluting coal-burning power plants in the United States emitted 20 tons of toxic mercury into the air in 2007, finds a new report from the nonprofit Environmental Integrity Project. Of the top 10 mercury emitting power plants, all but one reported an increase as compared to 2006.

Once released into the atmosphere, mercury settles in lakes and rivers, where it moves up the food chain to humans who eat contaminated fish. The Centers for Disease Control has found that six percent of American women have mercury in their blood at levels that would put a fetus at risk of neurological damage.
. . . .

 

[turbo]

We don't have any coal-fired power plants in Maine, but we are downstream from power plants in the mid-west, and our lakes, ponds, streams, etc are being polluted with mercury, which bio-accumulates in larger fish, as explained by alxm. As a result, the state has issued fish-consumption advisories telling all people to limit their consumption of wild-caught fish, with even tighter guidelines for children and women of child-bearing age. In general, it is recommended that adults eat no more than one meal a week of trout or salmon, and no more that 2 meals a month of other fresh-water fish, though there are specific (and far more restrictive) guidelines for some rivers/watersheds, including some areas from which no fish should be eaten by anybody. Coal power is cheap for the producer, and very costly in terms of environmental degradation for people down-wind of their plants.

 

[epenguin]

If still of interest. For any element both the toxicity and the transport (i.e. where it gets and how) depends on the chemical form. e.g. not all "arsenic" is at all equally toxic, it depends on the oxidation state. Methyl mercury is concentrated by fish. There was at least one famous case of a whole community disaster due to methyl mercury in Japan. There is a lot of info out there if you google for it. You might care to look at http://www1.american.edu/TED/MINAMATA.HTM and http://www.inchem.org/documents/ehc/ehc/ehc086.htm http://en.wikipedia.org/wiki/MTBE http://www.articlearchives.com/environment-natural-resources/pollution/1034606-1.html Mercury is methylated by microorganisms and thence gets into fish. Another way it used to get into the environment is inorganic and organic mercury compounds were used in antifouling ships' paint - precisely because of their biotoxicity.

According to the reference below, certain plants even accumulate mercury as metal droplets. http://books.google.it/books?id=jfQ...X&oi=book_result&ct=result&resnum=1#PPA679,M1