Plants play a key role in cycling toxic mercury levels in the environment

Scientists investigating gaseous mercury in the atmosphere in an attempt to reduce global pollutants have now discovered that a large amount of this harmful element is consumed by plants, causing it to accumulate in soils.

Every year, hundreds of tons of mercury are released into the atmosphere in the form of gas as a result of mining, burning coal, and other natural and industrial activities. Plants absorb these gas emissions in a manner similar to how they absorb carbon dioxide.

When the plants die or shed their leaves, the mercury is shifted to the soil, where huge quantities of the same element end up in watersheds, endangering animals and humans who consume contaminated fish.

According to Daniel Obrist, professor and chair of the Department of Environmental, Earth, and Atmospheric Sciences at the University of Massachusetts Lowell (UMass Lowell), long-term exposure to high levels of mercury can cause cardiovascular and neurological issues in humans. Obrist is heading the research team.

Obrist is also an expert on the cycling of environmental mercury. In his new research work, he and Jun Zhou, a Research Associate from UMass Lowell, collected over 200 published studies that contained information about mercury levels in vegetation from over 400 sites worldwide.

During the analysis of this data, the researchers found that about 88% of the mercury present in plants comes from plant leaves that absorb mercury gas from the air. According to Zhou, vegetation around the world can absorb over 1,300 tons of mercury every year, which accounts for 60% to 90% of the accumulation of this element on land.

The study results were recently published in the academic journal, Nature Reviews Earth & Climate. According to the team, the new study provides the most comprehensive review of mercury uptake in vegetation and its effect on mercury cycling across the world.

When I walk outside here in New England, I am always amazed at the greenness of our forest, grasslands and salt marshes. One goal of my research is to determine how strongly vegetation controls the cycling of elements—some of which can be toxic pollutants—so we can better mitigate damaging effects.”

Daniel Obrist, Professor and Chair of Department of Environmental, Earth and Atmospheric Sciences, University of Massachusetts Lowell

According to Zhou, the study offers scientists a better understanding of the mechanism of mercury cycling.

Researchers have worked on the role that vegetation plays on cycling of mercury for over 30 years now, but the full extent of these impacts are still not yet fully realized. It was timely to write this comprehensive review and communicate to colleagues and the public about the current state of knowledge in this area.”

Jun Zhou, Research Associate, University of Massachusetts Lowell

Researchers from the Environment and Climate Change Canada’s Air Quality Research Division in Quebec and the University of Basel in Switzerland have also contributed to the research work. The study was funded by the U.S National Science Foundation and the Swiss National Science Foundation.

In another but related project work headed by Obrist, researchers continue to assess how vegetation has an impact on mercury cycling in New England forests, targeting those in Massachusetts and Maine.

Obrist’s research team is now using a wide range of sensors and instruments to quantify the uptake of atmospheric mercury by forests at numerous heights from above the tree canopy close to the forest floor, enabling regular monitoring of how the deposition of mercury is likely to differ in each forest and tend to change with the seasons.