Several years after scientists thought they had put the problem to rest, they have once again discovered increasing concentrations of mercury, this time in rainwater. “It’s a surprising result,” says David Gay from the University of Illinois at Urbana–Champaign, who is a co-author on the new study. “Everybody expected [mercury levels] to continue going down. But our analysis shows that may not necessarily be the case.”
The results, recently published in Science of the Total Environment, is surprising because long-term trends had shown a decrease in mercury emissions whereas data collected between 2007 and 2013 indicate an unsettling upturn from the Rocky Mountains to the Midwest. The trend, however, is not due to regional activity. The authors speculate that because the U.S. has controlled its emissions since the 1970s, the toxic element was initially released via coal-burning power plants in Asia, drifted through the upper atmosphere for months, hit turbulence over the Rocky Mountains and was then pulled from the air in the form of rain.
It is possible that the calculated rise of 2 percent per year will result in a large accumulation in the ecosystem over the coming years, Weiss-Penzias says. “And once an ecosystem is contaminated with mercury, it can take decades for it to become uncontaminated.”