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Managing Mercury in Air

On February 16, 2012, the United States Environmental Protection Agency (EPA) promulgated a National Emission Standard for Hazardous Air Pollutants (NESHAP) regulation to reduce toxic air pollutant emissions from coal-fired and oil-fired electric generating utilities. This action is also known as the Mercury and Air Toxics Standards (MATS) rule. The promulgated toxics rule reduces emissions of heavy metals, including mercury (Hg), arsenic, chromium, and nickel, and acid gases, including hydrogen chloride (HCl) and hydrogen fluoride (HF). These toxic air pollutants, also known as hazardous air pollutants or air toxics, are known or suspected of causing cancer and other serious health effects.

In December of 2018, the EPA issued a proposal to reconsider the finding that it is "appropriate and necessary" to regulate hazardous air pollutant (HAP) emissions from coal- and oil-fired Electric Utility Steam Generating Units (EGUs) source category. EPA states the original analysis is flawed because it does not provide a full and fair accounting of the costs and benefits associated with implementation of the MATS rule. New York State and other Northeast States submitted comments to the docket disagreeing with EPA. DEC directly challenged EPA's cost/benefit analysis and listed examples of how the MATs rule has been successful.

Mercury Management in New York State

Diagram of Mercury cycle
The Mercury Cycle.
(click on image to see a larger view)

Human-caused (anthropogenic) emissions (past and present) have resulted in increased concentrations of mercury in the environment. According to the 2014 National Emission Inventory, approximately 52 tons of mercury are emitted from U.S. manmade sources every year. Over 43% of these emissions are from fossil fuel combustion sources and waste combustion. The global input to the atmosphere of all sources of mercury (including natural, oceanic and manmade) is calculated to be approximately 6,500 tons per year. Some of the mercury circulating through today's environment was released years ago. Land, water, and other surfaces can repeatedly re-emit mercury into the atmosphere after its initial release into the environment. Globally, artisanal and small-scale gold mining is the largest source of anthropogenic mercury emissions (37%), followed by coal combustion (24%). Other large sources of emissions are non-ferrous metals production and cement production. (United Nations Environment Program, Global Mercury Assessment, 2013).

The majority of mercury in the atmosphere is in the form of gaseous elemental mercury, Hg(0). This form of mercury can travel long distances in the atmosphere for many months.

Some Hg(0) is converted into 2 other forms of mercury:

  1. a more water soluble form of mercury, divalent or oxidized mercury, Hg(II); and
  2. Hg(0) can bind with particulate matter or aerosols to form particulate mercury, Hg(p)

These two forms of mercury are rapidly removed from the atmosphere in precipitation and fall onto land and into waterbodies, including the ocean.

In a waterbody and in the sediments of the waterbody mercury may be converted by bacterial action into an organic form, methylmercury, CH3Hg. Acidic lake conditions are believed to promote this conversion. Methylmercury can bioaccumulate up the food chain as a result of the ingestion of the contaminated aquatic organisms. Large fish and aquatic mammals at the top of the food chain may contain dangerously high levels of methylmercury. Contaminated fish become a human health hazard when they are consumed.

Methylmercury is slowly eliminated from the body. Animal studies and accidental poisonings have demonstrated that the embryo/fetus and young children are more sensitive to mercury than the adult. Methylmercury can travel across the placenta and accumulate in the fetal brain. It can also be found in breast milk. In the embryo/fetus and young children methylmercury has been shown to inhibit the normal development of the nervous system and produce generalized lesions throughout the brain. Lower levels of exposure may not be apparent until later when the child's motor and verbal skills may be delayed or abnormal. Pregnant women may not show any effects, but their unborn children may be adversely affected. EPA has estimated that 8% of women of childbearing age in the general U.S. population have blood levels of mercury higher than the EPA's reference level for mercury.

In adults, methylmercury concentrates in the kidneys, liver and brain. Nephritis, as well as neurological and cardiovascular effects, may result in adults. In conclusion, neurodevelopmental deficits are the most sensitive and well-documented health effects.

By reducing mercury emissions to the atmosphere from anthropogenic (manmade) combustion sources we hope to reduce the level of mercury in fish flesh and decrease the subsequent threat to the health of humans and wildlife.

NYS Air Regulations that Control Mercury

  1. 6NYCRR Subpart 219-7, Mercury Emission Limitations for Large Municipal Waste Combustors that are Constructed on or before September 20, 1994. Promulgation of Subpart 219-7 lowered the mercury emission limit for large municipal waste combustor plants from 80 ug/dscm or 85% removal, whichever is less stringent, to 28 ug/dscm or 85% removal, whichever is less stringent. This regulation will reduce mercury emissions and subsequent environmental loading of mercury in New York and the Northeast.
  2. 6NYCRR Part 246, Mercury Reduction Program for Coal-fired Electric Utility Steam Generating Units. Promulgation of this regulation reduced the allowable emissions from generating units and required continuous monitoring to ensure compliance.
  3. 6NYCRR Part 212, Process Operations. Promulgation of this regulation established a High Toxicity Air Contaminant list that addressed mercury emissions and established mercury limits to avoid bioaccumulation.