CPR Perspective: Mercury Pollution: Protecting Mothers and Babies

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Note: CPR Member Scholar Lisa Heinzerling contributed to an earlier version of this CPR Perspective. She suspended her membership in CPR when she joined the Environmental Protection Agency, and rejoined after her departure from government service.

March 2010

The Issue
Whether the United States should impose more stringent pollution controls on the two largest remaining sources of mercury contamination in the human food chain: mercury cell chlor-alkali plants and coal-fired power plants.


Mercury is highly toxic to humans. Exposure to even small amounts of methylmercury, the most toxic form of this elemental metal, can lead to irreversible neurological damage. Methylmercury's neurodevelopmental effects place the developing fetus, children, and adults up to age 20 at particular risk. The most recent data also suggest adverse effects on the cardiovascular systems of adults. 

According to a recent study, one in ten women of childbearing age in the United States has a blood mercury level that would put a developing fetus at risk. This figure nearly triples for women who designated their ethnicity as “other” (i.e., who are Native American, Asian American, or from the Pacific or Caribbean Islands) – fully 27.4 percent of women of childbearing age in this group have blood mercury concentrations above levels determined by the Environmental Protection Agency (EPA) to pose a risk to those exposed in utero.

Humans are exposed to methylmercury primarily through the consumption of fish that has been contaminated by the deposition of mercury air emissions into surface waters – rivers, lakes, and streams, for example. Such contamination is both severe and widespread. Vast expanses of the waters that support fish on which humans rely for food are under fish consumption advisories due to methylmercury contamination. By the most recent tally, all 50 states, one U.S. Territory, the District of Columbia, and several tribes have issued advisories placing some or all of their waters off limits for those who would eat the fish they catch. As of 2008, 43 percent of lake acres and 39 percent of total river miles within the United States’ borders are under advisories for mercury. In addition, 100 percent of Lakes Superior, Michigan, Huron, and Erie and significant stretches of coastal waters are under advisories. The number and extent of advisories have increased steadily for the past 14 years. This widespread methylmercury contamination has prompted the EPA and the Food and Drug Administration (FDA) to issue the first national fish consumption advisory, warning against consumption of several species of fish   Mercury occurs naturally in the environment and is also produced by anthropogenic (human-made) industrial processes. The increase in such activities as the combustion of fossil fuels, the combustion of mercury-laden wastes, and the manufacture of chlorine using mercury cells during the industrial era has elevated the volume of mercury released into the environment. Mercury air emissions convert to methylmercury in rivers, lakes, and streams, becoming part of a complex cycle with local, regional, and global components.  


What People Are Fighting About

Sources of Pollution

Anthropogenic emissions in the United States are dominated by emissions from coal-fired utilities. Other sources, such as chlor-alkali facilities and gold mines, may contribute more modest quantities of mercury on a national scale, but often dominate local emissions inventories. EPA estimated that, as of 1999, coal-fired utilities emitted 48 tons of mercury per year. Other large source categories are industrial and commercial boilers, which contributed, respectively, 9.7 and 6.5 tons per year. Chlor-alkali facilities and gold mining and refining operations emitted the next largest amounts of mercury. A handful of other source categories rounds out the roster of mercury emitters. Although the emissions figures for each of these source categories have no doubt changed since the EPA gathered these data, these industrial sectors remain the largest contributors to anthropogenic mercury emissions in the United States. 

In the 1990s, the share of total U.S. mercury emissions contributed by coal-fired utilities was rivaled by emissions from two other source categories: medical waste incinerators and municipal waste combustors. However, sources in each of these other categories have reduced their emissions on the order of 90 percent, as a result of regulations issued by EPA under the federal Clean Air Act (CAA). As of 1999, medical waste incinerators had reduced their mercury emissions to just 2.8 tons per year and municipal waste combustors had reduced their mercury emissions to just 5.1 tons per year. At that time, coal-fired utilities remained unregulated and mercury cell chlor-alkali plants were not subject to meaningful mercury controls. 

EPA Purports to Act

In December, 2003, the Bush EPA announced a long-awaited proposal for regulating mercury emissions from coal-fired utilities. In March, 2005, EPA issued the final version, which it dubbed the Clean Air Mercury Rule (CAMR). Before the 2003 proposal was issued, EPA had been widely expected to require coal-fired utilities to achieve a 90-percent reduction in mercury emissions – from approximately 48 tons to five tons – by 2007. Instead, EPA promulgated a rule that would permit coal-fired utilities to continue to emit more mercury for a longer time. In fact, although EPA announced that its CAMR would require a 70-percent reduction in mercury emissions “when fully implemented,” its own models showed that the promised reductions would not in fact be realized until sometime after 2020, and perhaps as late as the 2030s. This delay was the result of the method EPA chose to drive reductions.  Rather than simply issuing a regulation limiting emissions, EPA opted for a cap-and-trade approach, a startling departure from the ordinary process for regulating air toxics under section 112 of the Clean Air Act (CAA). EPA’s decision rested on an unprecedented interpretation of its authority under the CAA. 

As for chlor-alkali plants, the Agency in December, 2003 imposed a set of toothless requirements that ask plant personnel to visually inspect giant mercury cell rooms for fugitive emissions, a pointless exercise because mercury vapor is generally invisible to the naked eye.

Downsides of Mercury Trading

EPA's attempt to apply the tool of cap-and-trade to the problem of mercury met with a raft of criticism – not . surprising given the high stakes for public health. The critical attention was warranted because cap-and-trade, like other regulatory tools, has strengths and weaknesses that make it well suited for some environmental problems but ill suited for others. Because mercury is so toxic, because it is very persistent in the environment – that is, it does not break down into less dangerous components but instead stays around for a very long time – and because mercury emitted to the air deposits locally, regionally, and globally, the unrestricted buying of allowances to pollute could easily lead to "hot spots" of pooled contamination that threaten specific communities. (See CPR's Perspective on Emissions Trading for further analysis of these problems).

Another weakness of EPA's cap and trade rule is the actual level of control selected. Whether one employs a cap-and-trade approach or a technology-forcing standard, the key to how much protection is provided is the level of control or emissions set by the agency. In the CAMR, EPA set overall caps (or limits) to be imposed on total emissions at 38 tons per year (TPY) by 2010 and 15 TPY by 2018. The Agency then allocated "allowances" authorizing sources to emit up to the aggregate level set by the cap. Sources were then authorized to trade allowances among themselves – buying and selling in order to ensure that each source holds allowances sufficient to cover its relatively larger or smaller quantities of mercury emissions. 

A close look at EPA's approach reveals that the caps EPA set were extraordinarily weak. The first-phase cap, to have been met by 2010, would have required no reductions beyond those already to be realized as "co-benefits" of other regulatory controls sources must already comply with. And the second-phase cap, to have been effective in 2018, would have allowed sources to "bank" (or save) allowances, enabling aggregate emissions to exceed the cap if sources were to decide to hoard allowances. EPA models projected a mere 50-percent reduction in emissions by 2020. These very modest – and delayed – reductions in a toxic metal known for persistence in the environment would have translated into an unjustified windfall for coal-fired utilities at the expense of future generations’ health. 

Environmental Justice: Hot Spots and Risk Avoidance

EPA's approach also raised a host of environmental justice issues. As framed, the cap-and trade proposal would have disproportionately burdened various fishing tribes and indigenous peoples, other communities of color, and low-income communities that depend on fish. As amply demonstrated by the National Environmental Justice Advisory Council, the fish-consumption practices of these groups differ considerably from those of the "typical U.S. consumer" that was the apparent focus under EPA's approach. Members of these groups consume more fish, at greater frequencies, contaminated at higher levels – with the result that they are more highly exposed than members of the general population. Members of these groups are thus the ones relatively likely to suffer the adverse health effects of increased mercury emissions over a longer period of time. For some groups, the harms resulting from the delayed and limited emissions reductions may also be felt along interrelated economic, social, cultural, spiritual, and political dimensions. This is the case, for example, for the various Ojibwe tribes and other fishing tribes of the upper Great Lakes. 
As mentioned earlier, EPA's approach introduced the problem of "hot spots" – local or regional instances of relatively concentrated emissions and, ultimately, relatively high exposure. EPA's cap-and-trade approach expressed the relevant caps in terms of total mercury emissions and allowed mercury to be traded freely among sources anywhere in the United States. By design, it said nothing about how the emissions were distributed within this nationwide boundary. The potential for perpetuating or exacerbating hot spots has long been recognized as the Achilles heel of cap-and-trade approaches. The likelihood that such hot spots would coincide with areas that are home to tribes and indigenous peoples, communities of color and other low-income communities was a concern under the CAMR.
EPA claimed in the preamble to the proposed rule that it "does not expect any local or regional hot spots" under this national cap-and-trade approach. EPA reaffirmed this claim in the final rule, but without addressing fully the substantive arguments raised by commenters. Indeed the potential for hot spots was among the most controversial and commented-upon issues, with even the Government Accountability Office and EPA's Inspector General questioning EPA's claim on this point. Moreover, EPA's own models suggested reason for concern. For example, available data pointed to the possibility of local and regional hot spots in the upper Great Lakes states of Michigan, Minnesota, and Wisconsin. These hot spots may have affected even members of the general population in this region, given their higher than average rates of fish consumption. And they would have imposed a profound burden on the fishing tribes, whose practices place them among the most highly exposed and who have rights, secured in many instances by treaty, to continue to rely on fish as they have in the past. 
Additionally, EPA's rule relied heavily on risk avoidance – that is, it asked those who would bear the risks of unabated mercury contamination to forego eating fish in order to protect themselves. EPA conceded in the preamble to the proposed rule that those who regularly consume fish – who it unflinchingly acknowledges will be "Native Americans, Southeast Asian Americans and lower income subsistence fishers" – particularly children up to age 20 and women of childbearing age – are at greater risk than the "typical U.S. consumer."  EPA suggested that these people take on the responsibility of avoiding these risks. It referred them to advisories that ask them to eat less fish or different species or to stop consuming fish altogether – despite the widely recognized health benefits of eating fish. The EPA’s embrace of risk avoidance – as a substitute for reducing the risks by preventing mercury contamination in the first place – was likely to burden disproportionately fishing tribes and other higher consuming subpopulations. It was to these groups that EPA addresses this "response." And while giving up fish for some individuals may mean finding less palatable substitutes in terms of protein and other nutrients or expending more time and money to travel to less contaminated waters to fish, giving up fish for other individuals may be impossible. For example, members of the various Ojibwe and other fishing tribes of the upper Great Lakes value fish and fishing for physiological, economic, social, political, cultural and spiritual reasons. The burden imposed by contaminated fish is thus not only different in degree, but also different in kind, from the burden imposed on the general population. 

Distorted 'Costs' and 'Benefits'

EPA attempted to justify its final mercury rule by arguing that the costs of obtaining mercury reductions from coal-fired utilities outweighed the benefits of doing so. EPA came to this conclusion by narrowly defining the benefits of mercury emissions reductions, by invoking assumptions about exposure that systematically undercount those affected, and by discounting all benefits realized in the future. While these infirmities are typical of cost-benefit analysis in other contexts, a few analytical distortions warrant particular note. (For more information on this troubled process, see CPR's Perspective on Cost-Benefit Analysis.)
First, EPA made several crucial cuts in its benefit calculus: it counted only benefits to human health (and so excluded ecological health and other benefits, including, e.g., economic, social, political, cultural and spiritual well-being for the fishing tribes), and of these human health benefits, it counted only neurodevelopment effects and so excluded cardiovascular and other effects. It further winnowed the benefits, by counting only neurodevelopment effects that are captured by IQ decrements. Various independent analyses have demonstrated that quantifying these excluded benefits would reverse the conclusion of the analysis, with the benefits of mercury regulation dwarfing the costs. 
Second, EPA narrowly circumscribed the exposed population, counting only prenatally exposed individuals whose mothers eat freshwater fish caught by recreational anglers on inland U.S. lakes. Among the exclusions were all those exposed during childhood, all those exposed via ingestion of freshwater fish caught commercially on inland U.S. lakes, and all those exposed via ingestion of non-freshwater fish caught recreationally or commercially in coastal or other waters
Third, EPA made an extraordinary judgment regarding social good: it counted losses in future earnings as a cost of mercury contamination, but it counted as a benefit of mercury contamination the money the government saves because children with lower IQs (as a result of mercury exposure) need fewer years of school. Under this startling approach, a weak rule was preferable, because it preserved the "benefits" of lower IQs due to mercury contamination. Then, using a discount rate of 3 percent, EPA determined that each IQ point decrement avoided would net a mere $8,807 in benefits (a figure that is reduced to $1,580, it points out, if a 7-percent discount rate is used). 

Legal Challenges

Several states, tribes, and environmental groups filed lawsuits challenging the final rule, arguing that EPA had misinterpreted its authority under the Clean Air Act when it eschewed the ordinary processes under section 112 of the CAA in order to instate its cap-and-trade program. The D.C. Circuit agreed, vacating and remanding the rule. Although the Bush Administration had petitioned the U.S. Supreme Court to hear the case, the Obama Administration withdrew this petition when it came into office. 

Thus, EPA has been sent back to the drawing board, instructed to issue a rule for coal-fired utilities that is consonant with the CAA. The EPA has now committed to issuing a MACT standard for these sources by 2011, pursuant to a court-ordered deadline. In the meantime, years have elapsed, during which mercury emissions from this largest category of emitters remained unregulated by the EPA. The costs of this delay to human and environmental health are extraordinary.   

Chlor-alkali Plants

Chlorine manufacturing also contributes significantly to mercury emissions in the United States. Notably, the use of mercury in the manufacture of chlorine and caustic soda (NaOH) is entirely unnecessary in the first place. Unlike coal-fired utilities, which emit mercury as an unintended but inevitable byproduct of burning coal, mercury cell chlor-alkali facilities employ an outmoded process that intentionally uses large amounts of mercury as a flowing cathode in an electrolytic cell. But alternatives to this process have been around for more than 30 years – alternatives such as a diaphragm or membrane cells that use no mercury at all. All but four of the facilities that manufacture chlorine and caustic in the United States now use diaphragm or membrane cells, which are significantly more energy efficient and do not involve mercury. Indeed, the process used by these four remaining mercury cell chlor-alkali plants is so outdated that a new facility of this sort has not been built in 30 years. 

Additionally, mercury cell chlor-alkali plants "lose" some amount of mercury each year during the manufacturing process – as much as 65 tons, by some estimates, although the precise amount is disputed. Because mercury effectively catalyzes the chemical reaction that produces chlorine and caustic soda, the amount of mercury at each facility should theoretically remain unchanged. But this is not the case in practice, and these plants have continued to need to purchase additional mercury. The industry claims that the missing mercury condenses and accumulates in pipes, tanks, and other plant equipment; environmentalists contend that the missing mercury escapes as fugitive emissions. Although the industry has recently made some effort to account for some of the missing mercury, it remains the case that it is unable to account satisfactorily for all of the mercury purchased by chlor-alkali facilities. EPA concedes that "the fate of all the mercury consumed at mercury cell chlor-alkali plants remains something of an enigma." Significantly, this missing mercury is not included in estimates of total U.S. mercury emissions.
Yet, when it had the opportunity, EPA failed to implement a “maximum achievable control technology” (MACT) requirement that provides incentives for these four plants to modernize, preferring instead to prop them up for the foreseeable future by treating them as a separate "subcategory" with more lenient requirements than the other sources in the chlorine manufacturing category. Instead, EPA issued a rule in December 2003 that bestowed special treatment on the remaining mercury cell chlor-alkali plants within this source category, failed to address the missing mercury other than by "work practices" requirements that are likely impossible to enforce, and permitted these antiquated facilities to continue to operate indefinitely with only the tiniest of reductions in mercury emissions. Beyond visual inspections of invisible emissions, EPA has asked chlor-alkali plants to report the quantities of virgin mercury added to the mercury cells in the five years preceding the rule's compliance date of December 19, 2006. But it makes no promises to do anything with this information. 
With the EPA having failed to take meaningful action, U.S. Rep. Jan Schakowsky (D-IL) has stepped in, introducing a bill (H.R. 2190, known as “The Mercury Pollution Reduction Act”) that would phase-out the mercury cell process entirely. 

Gold Mines

Gold mines emit mercury into the air, primarily in the process of roasting the ore, and collectively they account for just a fraction of national mercury emissions. However, as in the case of mercury cell chlor-alkali plants, emissions from individual facilities may dwarf those from individual coal-fired power plants. The average coal-fired power plant emits approximately 250 pounds of mercury per year. Yet a single mine in Nevada emitted 9,400 pounds of mercury in 1998; at another, mercury emissions were 2,200 pounds. The magnitude of these contributions has only relatively recently come to the fore, since the Toxic Release Inventory (TRI) rules required gold mines to begin reporting their discharges of mercury in 1998. 
EPA's response to these TRI data is still taking shape, more than a decade later. Among the options is a MACT standard under section 112 of the CAA, which, as noted above, is the standard approach to regulating emissions of hazardous air pollutants, including mercury. Throughout the Bush Administration, however, EPA refused to go this route, leaving emissions control to voluntary measures. EPA's Region Nine and the Nevada Department of Environmental Protection (NDEP) instituted a "voluntary mercury air emissions reduction program" or "VMRP" for the four largest emitters in Nevada. According to the TRI data, these sources together emitted 13,560 pounds of mercury, accounting for roughly 90 percent of mercury emissions from Nevada gold mines. Under the VMRP, these four sources undertook process changes which, according to EPA, resulted in a 40-percent reduction in emissions from the baseline by the end of 2002 and a 75-percent reduction by the end of 2003. In May, 2006, NDEP altered course somewhat and promulgated a rule that made mandatory any controls that the four sources had undertaken; expanded the program to include all of the precious metal mining operations in Nevada with the potential to emit mercury, which NDEP estimates to be 19 in number; and instituted enforceable operating and reporting requirements through a permit system. 
The emissions reductions that Nevada has been able to secure are laudable, so far as they go. However, the regulatory response the mercury emissions from gold mines is instructive, revealing the weaknesses of relying on voluntary approaches compared to the mandatory hybrid of technology-based and health-based standards embodied by the MACT approach. First, the quality of the emissions figures on which these claims are based is unclear. Although the 1998 TRI data show total emissions from the four sources to be 13,560 pounds per year, in calculating the touted VMRP reductions, EPA used a baseline figure of 21,098 pounds per year, based on revisions to the 1998 data. Several knowledgeable observers have questioned this baseline and, thus, the claims that flow from it. Second, the Bush-era decision not to promulgate federal MACT standards means more limited protection for public health. The claimed 75-percent reduction in emissions from the four largest Nevada mines is more modest than the 90-percent reduction typically required by MACT. Moreover, the NDEP regulations fail to incorporate the mandatory residual health-based standard as would a MACT approach under section 112 of the CAA. Health and environmental agencies, environmental groups, and others in Idaho and Utah – downwind of the Nevada gold mines – have expressed many of these concerns. Meanwhile, in 2005, Utah issued its first state waterfowl consumption advisory, warning against the consumption of two species of wild duck found to be highly contaminated with mercury. Finally, the NDEP regulation applies only to mining operations in Nevada, whereas a federal MACT standard would apply nationwide. 
Now, in the new Obama Administration, the EPA has announced that it intends to promulgate a federal MACT standard by April, 2010 and to finalize a rule by December, 2010. 
A Progressive Perspective

In addressing mercury emissions from coal-fired power plants and chlor-alkali plants, EPA faced a legally straightforward task. In the case of power plants, section 112 of the Clean Air Act lists mercury as a hazardous air pollutant subject to regulation, and EPA had previously concluded that power plants should be regulated as sources of mercury emissions. Under the clear language of section 112, listing of mercury and of this source category led to an obligation on the part of EPA to regulate mercury emissions by prescribing MACT and requiring its installation. A MACT directive would have required each individual source to reduce its emissions to the level achieved by the best performers in its source category. By many accounts, this would have meant reducing mercury emissions by as much as 90 percent, within the tight three-year deadline provided by section 112 – reductions that we would, by now, have seen. The meaningful regulation of these sources, as promised by the Obama Administration, would be a welcome development.

EPA's chlor-alkali rule remains utterly inadequate. EPA cannot simply cite the "enigmatic" nature of the mercury that is unaccounted for in the mercury cell process; EPA must find and reduce, through enforceable MACT requirements, emissions of any "lost" mercury. 
In addressing mercury emissions from gold mines, EPA needs to move quickly and boldly to promulgate a MACT standard under section 112 of the CAA. Indeed, given the current extraordinary price for gold, there is particular cause for concern that sources' voluntary undertakings may give way to expediency in processing the ore in order to bring it rapidly to market. In any event, EPA needs to ensure that the emissions data on which it relies are accurate. 
Clearly the Obama Administration has been left in a deep hole, dug by a Bush Administration that was hostile to regulating mercury. The Obama EPA’s early steps on mercury are laudable. Still, there is cause for lament over the years that have been lost and the toll that this delay has exacted in terms of human and environmental health. With each year that the EPA failed to act, the costs of this delay piled up. Taking into account just the neurological harms, consider that as many as 637,000 children have been born each year with elevated blood mercury levels  – levels associated with cognitive dysfunctions including IQ losses.
Finally, as a general matter, EPA should address the harms of mercury contamination by risk reduction, rather than risk avoidance. That is, EPA needs to require sources to prevent or reduce their mercury releases, rather than ask those exposed to protect themselves by taking steps to avoid exposure – here, by reducing or eliminating fish from their diets. Given what is at stake from mercury contamination and given the serious losses that for many accompany having to avoid consuming fish, risk avoidance is an inappropriate regulatory tool in this context.

For Further Information


  • Lisa Heinzerling and Rena I. Steinzor, A Perfect Storm: Mercury and the Bush Administration, 34 ENVT'L. L. REP. 10297 (2004)
  • Lisa Heinzerling and Rena I. Steinzor, A Perfect Storm: Mercury and the Bush Administration, Part II, 34 ENVT'L. L. REP. 10485 (2004)
  • Catherine A. O'Neill, Mercury, Risk and Justice, 34 ENVT'L. L. REP. 11070 (2004)
  • Catherine A. O’Neill, The Mathematics of Mercury, in Reforming Regulatory Impact Analysis 108 (Winston Harrington et al., eds.) (2009)
  • Rena I. Steinzor, Mother Earth and Uncle Sam: How Pollution and Hollow Government Hurt Our Kids 103 (2008).