Water Quality Update: Mercury
Coming Soon To A Water Quality Permit Near You!
Under the new Method 1631, many municipal and industrial facilities that use and discharge water are experiencing changes in their mercury monitoring requirements. This means that some facilities must test for mercury for the first time, while other facilities that had been monitoring mercury previously must test at levels 400 times lower than before.
On September 1, 2003, Method 1631, Revision E became effective, and the U.S. Environmental Protection Agency (EPA) is issuing its first water quality criteria for methylmercury under the Clean Water Act (CWA).
Method 1631 is much more sensitive than previous methods. Rather than measuring mercury in parts per billion, Method 1631 measures it in parts per trillion. [One part per trillion is approximately equal to one pinhead sized drop of mercury in an Olympic sized swimming pool!]
Humans are believed to be exposed to methyl mercury mostly through fish consumption. Most of the mercury entering the aquatic environment is believed to be the result of so-called "atmospheric deposition" -- air emissions that are transported through the atmosphere and eventually deposited on land and water surfaces. Once mercury enters water, biological processes transform it to a highly toxic form (methylmercury) that builds up in fish and in the animals that eat fish.
Methylmercury in humans has been linked to adverse health effects such as nervous disorders,
tremors, inability to walk, convulsions, and in some cases, even death. Mercury exposure has also been linked to a variety of abnormalities in developing fetuses.
The water quality criteria for methylmercury is to be used by states in determining methylmercury levels in fish tissue. The new criteria are based on a risk assessment that EPA has developed in response to recommendations made by the National Academy of Sciences.
Methylmercury’s criterion is now expressed as a fish tissue value of 0.3 mg/kg, rather than as a water concentration; this reflects scientific consensus that consumption of fish and shellfish is the main human route of exposure to methylmercury.
EPA plans to develop guidance to assist states with implementing the methylmercury criterion. States are expected to adopt or revise the new criteria by 2004. Stay Tuned!
Mercury Levels in Fish
| Species |
Mean - ppm |
Range - ppm |
# of Samples |
| Swordfish |
1 |
0.10 - 3-22 |
598 |
| Shark |
0.96 |
0.05 - 4.54 |
324 |
| Tuna |
0.32 |
ND - 1.30 |
191 |
| Lobster |
0.31 |
0.05 - 1.31 |
88 |
| Catfish |
0.07 |
ND - 0.31 |
22 |
| Salmon |
ND |
ND - 0.18 |
52 |
| Oysters |
ND |
ND - 0.25 |
33 |
| Shrimps |
ND |
ND |
22 |
Data source: FDA database FY 85-99
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