By Jack Thorndike

Mercury is one of the most well-known toxic metals, having been implicated in accidental poisonings, ill-advised medicinal ingestion, and even assassination attempts. Today, mercury pollution poses significant public health dangers, particularly when it enters aquatic ecosystems and reaches harmful concentrations in commercial fish stocks. In most cases, mercury pollution starts with industrial emissions into the atmosphere, which have steadily increased since the 1880s. Now some researchers say we’re on track to produce a surge in mercury pollution as terrestrial deposits of old mercury pollution are released by climate change.

A perspective by David Krabbenhoft and Elsie Sunderland recently published in Science details how legacy mercury pollution is likely to be released more quickly in a warmer planet. Atmospheric mercury deposited on land mostly remains sequestered in soils and plants, and historically has been released into aquatic environments in cycles lasting decades or centuries. Krabbenhoft and Sunderland expect this process to accelerate with climate change, leading to a surge of mercury pollution that could provoke a public-health crisis at the top of the food chain, where humans feed. The primary triggers, they argue, are increased erosion and wildfires.

Noting that soil is the largest repository of anthropogenic mercury, Krabbenhoft and Sunderland describe a scenario in which climate change-driven increases in storm intensity exacerbate erosion, leading to the release of stored mercury into wetlands, waterways, and oceans. Once released from the soil into water, the mercury can bioaccumulate in fish and, ultimately, impact human health through the food chain. 
In addition to causing more extreme weather, climate change is expected to dry out many regions of the earth. As mid-latitude regions get drier, areas that frequently burn now -- like Australia and the American west -- will become more incendiary, while boreal, tundra, and taiga regions will burn for the first time. Forests, grasslands, and tundra have been repositories of mercury pollution for centuries and, as these areas experience wildfires with increased frequency and intensity, additional mercury will enter the atmosphere. This increased atmospheric mercury load is expected to eventually be deposited into waterways and to find its way to the top of the aquatic food chain. 

"While we can’t do anything about legacy mercury pollution, humans can address the 2,000 metric tons that we inject annually into the atmosphere -- tomorrow’s legacy mercury pollution."

Krabbenhoft and Sunderland note that, while we can’t do anything about legacy mercury pollution, humans can address the 2,000 metric tons that we inject annually into the atmosphere -- tomorrow’s legacy mercury pollution. Projecting to the year 2050, researchers predict that, if we enact meaningful limits on emissions and account for other climate mitigation strategies, our annual mercury output could fall to 800 metric tons. Conversely, if we do little or nothing, mercury output is set to increase dramatically to 3,400 metric tons per year. 

Should we ever get serious about reducing mercury pollution -- and the resulting public health hazards -- a good step would be to eliminate coal-fired power plants which are responsible for 48% of US mercury emissions, in addition to 80% of CO2 from US power generation.  Additionally, the health care sector is working to reduce its own contributions to mercury pollution and climate change. A new initiative lead by the World Health Organization (WHO) and Health Care Without Harm, is aiming to end the manufacture, import and export of mercury-based medical devices by 2020. Learn more about this initiative and other global efforts to address mercury in health care at www.mercuryfreehealthcare.org. HCWH has also recently released Health Care & Climate Change: An Opportunity for Transformative Leadership, a report offering guidelines and case studies to help hospital leaders and facilities’ staff develop comprehensive strategies to reduce their reliance on fossil fuels through the use of clean technology.

Jack Thorndike is a freelance environmental journalist who writes about interactions between public health, ecosystems, and climate change.