Researchers highlight problem of legacy mercury in the environment

release and cycle a certain amount of mercury, blasting it out of rock with each volcanic eruption, but the new model developed at Harvard demonstrates that humans have been, and continue to be, responsible for the majority of the mercury currently found in the atmosphere, soil, and ocean.

“Ideally, mercury released by human activities would quickly be sequestered in the environment, but instead what we see is a huge quantity of it bouncing from one reservoir to the next,” explains senior author Elsie M. Sunderland, who is the Mark & Catherine Winkler Assistant Professor of Aquatic Science at the Harvard School of Public Health and an associate in environmental science and engineering at Harvard SEAS. “This means it continues cycling throughout the environment and persists for much longer timescales than most people realize, which has implications for long-term biological exposures.”

The new model quantifies the impact of historical emissions deduced from archaeological and anthropological research into artisanal and industrial techniques, and for the first time couples seven different environmental systems into one holistic and coherent model.

“This model is built on the best available science, and what it’s showing us is that if we want to reduce the amount of mercury in the environment, it’s not enough to simply stabilize the amount that we’re emitting,” says Amos. “We would need to dramatically reduce it.”

The results also draw attention to the contribution of historical emissions to the present-day mercury problem.

“Today, more than half of mercury emissions come from Asia, but historically the U.S. and Europe were major emitters,” says second senior author Daniel J. Jacob, Vasco McCoy Family Professor of Atmospheric Chemistry and Environmental Engineering at Harvard SEAS and Professor of Earth and Planetary Sciences. “We find that half of mercury pollution in the present surface ocean comes from emissions prior to 1950, and as a result the contribution from the U.S. and Europe is comparable to that from Asia.”

The release notes that other specific findings include the following:

• Anthropogenic emissions have increased the amount of mercury in the atmosphere, surface ocean, and deep ocean by factors of 7.5, 5.9, and 2.1, respectively, compared to natural conditions.
• 60 percent of the mercury currently being deposited in the atmosphere comes from legacy mercury, released by humans in the past, that continues to cycle throughout the environment. Only 13 percent of current mercury deposition is natural in origin. The remaining 27 percent comes from present-day anthropogenic emissions.
• At least half of the current anthropogenic mercury content of the surface ocean originated before 1950.

“The projections of atmospheric mercury deposition and ocean concentrations that have informed policymakers developing the recent global mercury treaty underestimated the amount of future accumulation, because they did not account for the full burden of legacy mercury in the environment,” notes Sunderland. “Our study reinforces the need for immediate and stringent emissions controls globally, to the extent technologically possible, to avoid future human health risks. Already, the costs of methylmercury exposure in Europe and the United States have been estimated at upwards of $15 billion.”

— Read more in Helen M. Amos etal., “Legacy impacts of all-time anthropogenic emissions on the global mercury cycle,” Global Biochemical Cycles (9 May 2013) (DOI: 10.1002/gbc.20040)