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We’re leading an all-out national mobilization to defeat the climate crisis.

Join our work today to help us build a thriving and just clean energy future. 

What Are Mercury and Air Toxics Standards (MATS)? Breaking Down EPA’s Proposed Rule

EPA just released its Mercury and Air Toxics Standards (MATS) Risk and Technology Review (RTR) proposal, which limits the amount of toxic chemicals that power plants can release. With no safe level of these substances, a strong standard is critical.

A coal power plant's cooling towers release exhaust over a neighborhood in the U.S.

You don’t have to be a scientist to work out that breathing in mercury and other toxic air pollutants is bad for your health—and bad for the planet. That being said, scientists would resoundingly agree. 

Some mercury does naturally exist in the earth’s crust. But human activities, including the extraction and burning of dirty fossil fuels, have led to widespread mercury pollution in the air that we breathe, the water that we drink, and the food that we eat. And the chief culprit, contributing the vast majority of mercury and other toxic air pollution, are coal-fired power plants, which burn and release the mercury found in fossil fuels into the atmosphere. 

Fortunately, about a decade ago, the Environmental Protection Agency (EPA) started regulating how much mercury and other hazardous air toxics those facilities can put into the air by setting Mercury and Air Toxics Standards (MATS). Trump’s EPA undid these life-saving rules, and now President Biden’s EPA just reinstated and somewhat strengthened the prior rules to further reduce mercury and heavy metals, especially at power plants that burn the dirtiest lignite coal. There is still more to do. But more on that later.

Blog Post Image - Quote Graphic

 Derivative of © 2008 LongitudeLatitude/Flickr CC BY 2.0 

First, what are mercury and air toxics?

Mercury is a highly potent neurotoxin, and exposure to it has often irreversible toxic effects including blindness, deafness, and affected coordination and speech. Toxic metals like mercury are particularly harmful because they don’t break down in the environment and can build up in the tissues of humans and animals. 

And the scariest part? Mercury air pollution isn’t bound by human-made borders. Mercury emitted into the air can travel thousands of miles before it’s eventually deposited back to the earth, meaning you don’t have to be near the source of the pollution to suffer from its effects. Afterward, it either settles into water or soil, where it often gets absorbed by fish or plants and later works its way up the food chain into humans. 

Nearly everyone has trace amounts of mercury in their system, given how pervasive it is in our environment. But some vulnerable populations, including pregnant people, young children, and those with compromised immune systems, face a higher risk when exposed. Mercury exposure has been linked to developmental problems in children, neurological issues, heart disease, and respiratory problems like asthma. 

Addressing mercury pollution from the biggest source—coal-fired power plants—can mean the difference between sickness and health, and often even life and death, for tens of thousands of people. Just like lead, there is no safe level of these substances. That’s why a strong MATS Risk and Technology Review (RTR) proposal from EPA is so critical. 


Mercury air toxics are a problem. What can a strong MATS rule do about it?

Over half of the coal-fired power plants across the country were built over 50 years ago without pollution-controlling technologies, and for most of the time since then, there were no national limits on how much mercury and other air toxics were allowed to be released into the air. Though it seems like a no-brainer to regulate this kind of deadly pollution, MATS safeguards have faced challenges over the years. 




Take a deeper dive: Here’s the history on MATS 

Back in December 2000, EPA determined that it was “appropriate and necessary” under the Clean Air Act to limit emissions of hazardous air pollutants like mercury, arsenic, benzene, and cadmium released from coal- and oil-fired power plants. However, despite this finding, the Bush administration never set a MATS standard. In fact, a MATS standard wasn’t set until 2012, when the Obama administration finally set a rule. Existing power plants were given a few years to meet the standards, and they ultimately took effect in 2015

Later that year, the U.S. Supreme Court (SCOTUS) ruled in Michigan v. EPA that EPA must further consider costs to industry, sending the rule back to EPA. In response, EPA published its supplemental findings on the costs and benefits of MATS, finding them to be justified in light of the enormous anticipated health benefits, and in 2016, SCOTUS denied the request by 20 conservative-led states to suspend the MATS standards, further upholding the “appropriate and necessary” finding. Behind this legal and bureaucratic saga, the irrefutable science remains clear: mercury and other hazardous air pollutants from power plants have devastating health and environmental impacts—but strong MATS safeguards can protect communities and save lives. 

Since the introduction of the MATS rule through 2021, EPA estimates that mercury pollution from power plants dropped 90 percent, acid gas pollution by 96 percent, and non-mercury metal pollution by 81 percent. Moreover, we’ve seen that as mercury pollution has decreased, public health has improved. During this same window, mercury levels in the blood of women in the U.S. declined by 34 percent and the number of children born with prenatal exposure to methylmercury levels above EPA’s reference dose was cut in half. Every year, the standards prevent 11,000 deaths and 130,000 asthma attacks among children. In short, these protections work and the last decade of data points to that success.

Defying and disregarding these massive steps forward for public health, the Trump administration went on to reverse the “appropriate and necessary” finding using flawed methods of review in 2020. This reversal intentionally and effectively weakened the life-saving MATS rule because it opened the door to lawsuits by coal and other oppugnant companies, which immediately followed. 

Fortunately, under the Biden administration, EPA corrected course and restored the “appropriate and necessary” finding in 2023 that Trump unwound and is now working to strengthen the MATS standard itself, based on technological advancements since the Obama-era EPA first set the standards in 2012.


This brings us to where we are today and EPA’s latest proposal: the Risk and Technology Review (RTR). This month, EPA released its MATS Risk and Technology Review (RTR) proposal. We read it (so you don’t have to) and break it down below.

Blog Post Image - Regan Porch

EPA Administrator Regan listens to residents of Houston, Texas talk about the impacts of pollution from nearby facilities on their community in November, 2021.

Here’s what you need to know about EPA’s MATS Risk and Technology Review (RTR) proposal— what does it say and why doesn’t it go far enough?

Under the Clean Air Act, EPA is required to review the MATS standard, at minimum, every eight years. That reconsideration process is referred to as the Risk and Technology Review (RTR). EPA’s recent RTR proposal found that the existing MATS rule could be strengthened in several ways. The RTR proposes the following updates:

  1. Lowering the limit for non-mercury heavy metals at all coal plants by two-thirds. These hazardous metal particles, including nickel, arsenic, and chromium, are referred to as “filterable particulate matter.” These pollutants could now be emitted at 0.010 lbs/MMBtu instead of 0.030 lbs. EPA estimates that 91 percent of coal plants already meet this lower standard. EPA is also seeking input on an even stronger standard of 0.006 lbs.
  2. Raising the mercury standard for the dirtiest coal plants that burn lignite coal, so that it is in line with the standard for non-lignite coal plants. The new standard is 70 percent lower than the 2012 level. This change would particularly benefit air quality in Texas and North Dakota, which host large lignite power plants.
  3. Requiring continuous emissions monitoring systems be installed at all coal power plants to ensure every plant is complying with the new standard for filterable particulate matter. These real-time monitoring systems will help bring environmental enforcement into the 21st century and are essential for ensuring public health improvements in fenceline communities.

Despite these developments, the proposal notably does not lower the mercury standard for most power plants. According to EPA’s own analysis, the rule as proposed would cause nationwide mercury pollution to fall by only 62 pounds by 2028, from 5,019 to 4,957 pounds. That is only a 1 percent decrease in mercury pollution.

To truly protect Americans’ public health from mercury and toxic air pollution, EPA should strengthen the baseline mercury standards for all coal-fired power plants. Many coal-fired power plants are already achieving lower emissions levels than this proposal requires, which shows that additional technological improvements are cost-effective and available. The agency should also opt for the more stringent filterable particulate matter standard of 0.006 pounds, which would improve public health for Americans near the 91 percent of coal plants that already meet the proposed standard of 0.010 pounds.

Remember Michigan v. EPA, where the court ruled EPA must consider the costs to the industry? Well, EPA projects that the MATS rule, as proposed, would create $170-220 million in health benefits and $170 million in climate benefits each year with compliance costs of only $33-38 million. This rule would be incredibly cost-effective at protecting public health—and takes important steps to reduce heavy metals and clean up lignite coal plants—but the agency is leaving much more significant health benefits on the table.

EPA will hold a public hearing on this proposal and will begin to take public comments soon before it finalizes the rule next year. Join Evergreen Action now and be the first to tell EPA: our public health can’t wait. Finalize the strongest possible MATS rule.