At a time when the government was partially shutdown and the EPA itself was running on borrowed time by using the last of its remaining funds for 2018 before generally shutting down itself over the last weekend of the year, the agency sought comments on whether it has the authority to rescind 2012 standards relating to caps on Mercury released by coal plants. Coal-fired power plants are the largest source of mercury in the United States. When mercury infiltrates the soil, it creates a neurotoxin that can lower IQ, cause increased risk of heart attacks, cause motor function deficits, and damage the nervous system.

The Mercury and Air Toxics Standards (MATS) have been a thorny issue since they were proposed in 2012. The rules have been the focus of much litigation by the coal industry and led to revisiting the EPA conclusions in 2015 and the current EPA reconsideration. Before MATS, there were no limits on power plant emissions of substances like mercury, arsenic, and other metals. The rules set forth technology based emissions standards that would need to be met within a certain time period. Many coal-fired power plants closed in response to the new standards claiming that it would be too expensive to install the technology necessary to achieve the emissions standards that were set. The expense factor is still one of the major arguments being employed. These standards were made in response to the EPA determination after years of study and the Clean Air Act Amendments that it was appropriate and necessary to control mercury emissions from power plants back in 2000. Previous attempts at finalizing a rule were struck down in court.

The EPA has not taken the step to change the current MATS rule yet. The agency issued a revised Supplemental Cost Finding for the MATS Standards. In its supplemental report, the agency estimated that it would cost coal and oil-fired power plants between $7.4 and $9.6 billion annually to comply with the rules. Based on these figures, the agency proposes to determine that it is not appropriate and necessary to regulate hazardous air pollutant emissions from these power plants since the quantifiable benefits are only between $4 and $6 million annually. Right now, the MATS rule would stay in place since the EPA has not yet proposed to remove coal and oil-fired power plants from the list of regulated sources under the Clean Air Act. However, it is likely that this would be the next step in the process after a finding that it is no longer appropriate and necessary to regulate these power plants.