How should cost factor into the protection of human health and the environment? That was the central question in a Supreme Court case last summer that pitted the coal industry and 20 U.S. states against the Environmental Protection Agency (EPA).

The court ruled that the EPA did not properly take into account what it would cost power plants to comply with new regulations to reduce the emission of mercury, a powerful neurotoxin. Now the EPA has until the self-imposed deadline of April 16 to come up with a cost consideration plan.

Elsie Sunderland, the Thomas D. Cabot Associate Professor of Environmental Science and Engineering, Shaun Goho, Senior Clinical Instructor and Staff Attorney in the Emmett Environmental Law and Policy Clinic at Harvard Law School, and Charles T. Driscoll, University Professor in Syracuse University's College of Engineering and Computer Science, recently co-authored a perspective piece, with a number of other experts, on this ongoing court case. The perspective was based on their comments submitted to the DC Circuit court on January 15, 2016.

After a review of the recent scientific literature, the authors concluded that the benefits associated with the reduction of mercury emissions far outweigh the cost to industry.

Three key points from their comments, published in Environmental Science and Technology, are:

The benefits of implementing of the Mercury Air Toxics Standards (MATS) are easily in the tens of billions.

In its initial cost-benefit analysis, the EPA estimated the direct benefits of mercury reduction to be $4 to $6 million. But that study is based on an extremely small subset of the population: children of freshwater recreational anglers in the U.S. The EPA chose this approach because these benefits of the regulation could be monetized using methods that everyone could agree on.

But if you consider all of the benefits of reducing coal-fired power plant mercury emissions, the benefits are easily orders of magnitude greater than those quantified by EPA. For example, one recent study found that the cumulative benefits associated with implementation of MATS exceeded $43 billion. Other work has estimated an annual benefit of $860 million associated with a 10 percent reduction in methylmercury exposure in the U.S. population.

Most benefits to human health and wildlife haven't even been monetized.

Many of these benefits are associated with cardiovascular health. The EPA did not quantify cardiovascular effects during the agency's initial assessment due to what can be described as "scientific uncertainty". However, an independent panel of experts sponsored by EPA in 2011 concluded that methylmercury has a substantial impact on cardiovascular health and should be incorporated into benefits assessments.

Methylmercury exposure has also been linked to poor endocrine function, risk of diabetes, and compromised immune health - none of which have been monetized yet. Nor have the impacts of methylmercury exposure on fish and wildlife been quantified and emerging evidence suggests these effects are much more severe than previously realized.

The EPA underestimated the benefits of mercury reduction from coal-fired power plants.

Recent research, in part led by Sunderland, has shown that local and regional efforts to reduce mercury emissions are doing better than expected in reducing human and wildlife exposure to methylmercury. This new science was not available to EPA in 2012 when the original analyses of benefits of mercury reduction were being assessed.

The past decade has already seen a substantial decrease in mercury emission from electric utilities as energy markets have shifted to cleaner natural gas. Some of this decrease is also a co-benefit of sulfur dioxide or nitrogen oxide emissions controls.

Those reductions are having measurable positive effects allowing researchers to be confident that regulating mercury emissions will have substantially greater benefits in the U.S. than previously thought.

"Through advances in mercury science, previously held assumptions that reductions in mercury emissions in the U.S. would have limited benefit to the mercury deposition and health benefits no longer hold," said Driscoll. "Those assumptions, which were integral to the assessment done by the EPA in 2012 that led to their recommendation to implement MATS, resulted in EPA underestimating the benefit of a reduction in mercury emissions."

When the EPA finalizes its cost consideration this spring, it will likely be challenged in court again. Sunderland, Goho and their colleagues believe that the public health benefits associated with limiting mercury emissions will be substantial.

"The Clean Air Act has been one of our country's greatest successes stories," said Goho. "Yet, when it comes to mercury and other toxic air pollutants, only one major source of emissions has escaped regulation for the last twenty-five years: coal-fired power plants. Power plants are the number one source of mercury emissions in the United States and limits on those emissions are long overdue."

"Methylmercury is potent neurotoxin that likely has significant cardiovascular impacts, is known to detrimentally affect birds, amphibians and mammals by affecting their reproductive success, has be identified an endocrine disrupter and is now being studied as an immunosuppressant," said Sunderland. "Nobody thinks more methylmercury in the environment would be a positive change."