When the Environmental Protection Agency adopted a rule last year that aimed to reduce mercury pollution through a cap and trade system, the agency downplayed the idea that the toxic metal is often deposited – in high concentrations – near its source. A study, published in the current issue of the journal BioScience, found as many as 14 such mercury “hot spots” in the Northeast, one with mercury levels five times higher than previously estimated by the EPA. This research adds to evidence that the EPA rule is inadequate and should be replaced with strict limits on how much mercury can be emitted.

According to the EPA, less than half of all mercury deposition within the United States comes from domestic sources. However, the agency adds, there are regional differences and U.S. sources represent a greater fraction of the total deposition in parts of the Northeast because of the direction of the prevailing winds.

Eleven scientists, including several from the BioDiversity Research Institute in Gorham took a closer look and found that this was misleading. The study, which was organized by the Hubbard Brook Research Foundation in New Hampshire, examined 7,300 samples from fish, loons and other wildlife from lakes and reservoirs from New York to Nova Scotia. Samples from 14 locations had unusually high mercury levels. One “hot spot” was in central Maine, at the headwaters of the Androsscoggin and Kennebec rivers. Scientists believe the drawdown of water from reservoirs along the rivers concentrated the mercury that was deposited there, raising the level in some locations to four times higher than the EPA deems acceptable.

The scientists closely examined a hot spot along the Merrimack River in southern New Hampshire and northern Massachusetts near four coal-fired power plants. They found mercury depositions in some locations nearly five times what the EPA predicted for the area. They estimate that up to two-thirds of the mercury was from local sources.

The Clean Air Mercury Rule, adopted by the EPA in March despite disapproval from the agency’s inspector general and the Government Accountability Office, calls for a 70 percent reduction in mercury emissions by 2018. It includes a cap-and-trade system that would allow power plants such as those near the Merrimack River to buy credits to continue polluting rather than reducing their emissions. That’s one reason why 16 states, including Maine, have sued the agency to stop the rule.

Sen. Susan Collins plans to reintroduce legislation to reduce mercury emissions from power plants by 90 percent, which the Clean Air Act previously required, and other to create a nationwide mercury monitoring network to track U.S. emissions to clarify the contradictions between the EPA and BioScience studies.

Such monitoring, while overdue, should clarify where mercury comes from and where it ends up. Based on this information, regulators and lawmakers can make better decisions on how and where to require reductions.