Mercury is a toxic metal that can be carried through air and water and causes major health problems.

Though mercury occurs naturally in rocks and minerals, human activities are responsible for much of the mercury released to the environment today.

Mercury is released to the atmosphere when coal or other fossil fuels are burned for energy, when electronic and medical waste is incinerated, and through industrial processes. This atmospheric mercury can travel long distances before falling as rain, snow, or microscopic particles and winding up in soils and surface waters.

Once in the water, the mercury can be converted to its most toxic form, methylmercury, which accumulates in fish and other aquatic organisms. When humans eat contaminated fish, we are exposed to methylmercury and its associated severe health problems.

The Concord River

Mercury in NEIWPCC States

Mercury poses a significant challenge in New England, especially since much of the mercury deposited here is emitted in other regions of the country. NEIWPCC and our member states have been very involved in this complicated issue.

NEIWPCC provides support to its member states by tracking and reviewing technical and policy issues related to mercury, coordinating regional mercury projects, and participating in national and regional groups focused on mercury. Most notably, we played a lead role in coordinating the Northeast Regional Mercury TMDL and the Northeast States’ Clean Water Act Section 319(g) Petition for Mercury.

Mercury Standards

EPA and all of the NEIWPCC states have established water quality criteria for mercury. These criteria protect aquatic life and allow for safe human consumption of fish. Some states have also set mercury criteria for drinking water.

EPA published a Methylmercury Criteria Document in 2001 that recommended fish tissue criteria to protect humans from methylmercury exposure through fish consumption. The criterion is 0.3 mg methylmercury/kg fish, which is the concentration in fish tissue that should not be exceeded based on a total fish and shellfish consumption rate of 0.0175 kg fish/day.

The EPA encourages states and authorized tribes to develop a water quality criterion for methylmercury using local or regional data rather than the default values if they believe that such a water quality criterion would be more appropriate for their target population. In the Northeast, Maine and Massachusetts have adopted methylmercury criterion for fish tissue of 0.2 and 0.3 mg methylmercury/kg fish, respectively.

For information on water quality criteria for other parameters, see our water quality standards matrix.

Aquatic Life Freshwater Acute 1.4 1.4 1.4 1.7 1.4 1.4 1.4 2.4
Freshwater Chronic 0.77 0.77 0.77 0.91 0.77 0.77 0.77 0.012
Saltwater Acute 1.8 1.8 1.8 2.1 1.8 N/A 1.8 N/A
Saltwater Chronic 0.94 0.94 0.94 1.1 0.94 N/A 0.94 N/A
Human Health Consumption of Water and Organisms N/A 0.05 N/A N/A 0.05 0.7* 0.14 0.14
Consumption of Organisms Only 0.3 mg/kg ** 0.051 0.3 mg/kg ** 0.2 mg/kg ** 0.051 7×10-4 0.15 0.15

All concentrations in µg/l unless otherwise noted.
* Applies to drinking water source only.
** Criterion is for concentration in fish tissue.

Additional Resources