Human activity is one of the major causes of climate change, and the introduction of the 2013 Minamata Convention, its subsequent ratification, and global legal enforcement aimed at mitigating global mercury (Hg) emissions have further highlighted this. Researchers found that atmospheric mercury levels have decreased by almost 70% in the last 20 years, mainly because human-caused emissions have been reduced.
Despite the decline in human-driven mercury emissions, re-emission from soil due to climate change presents a new challenge. According to research published in ACS ES&T Air, scientists discovered that currently, the soil emits significantly more mercury (62%) than human-related sources (28%).
Released by human activities and natural processes, mercury in its organic form, methylmercury, is highly toxic, and exposure, often through contaminated air, water, or food, can damage the nervous system, particularly in unborn children and young infants.
Over the decades, industrial activities like the burning of coal, waste incineration, and mining activities have created a persistent global mercury footprint, dispersing it far beyond urban centers and industrial zones.
The Breakthrough Discovery
To distinguish between new, human-caused emissions and re-emissions of terrestrial mercury stored in the soil, researchers can look at patterns of isotopes in the atmosphere. But regular atmospheric isotope measurements have been collected for only about a decade.
To look back in time, the researchers turned to the leaves of a tiny, low-to-the-ground perennial plant (Androsace tapete) growing at high elevations on Mount Everest. Much like the rings in a tree trunk, this plant grows a new layer of outer leaves every year, and they reflect what the plant’s surrounding environment was like. By sampling older leaves from the center of two plants on Everest, the team gained a sense of atmospheric mercury levels as far back as 1982.
They found that between 2000 and 2020, the total atmospheric concentration of elemental mercury decreased by 70%, with terrestrial mercury emissions making up a larger fraction of total emissions year over year at 62%.
“By tracking mercury pollution over four decades at the top of the world, we show that global efforts to reduce pollution are working; levels in the air around Mount Everest have dropped significantly in the last two decades,” explains Yindong Tong, the corresponding author on the study.
The Climate-Mercury Connection
Over time, as pollutants pile up, soil acts as a reservoir. The rising temperatures and changing climate patterns are triggering the release (re-emission) of this mercury. For instance, rising CO2 levels and temperatures can stimulate vegetation growth. As this vegetation decomposes, it can release mercury that was stored within the plant matter into the soil and the surrounding environment.
Moreover, as the Arctic warms, permafrost, which is permanently frozen ground, thaws. These thawing releases pollutants trapped within the permafrost, making it available to be released into the atmosphere and waterways.
Despite these emissions are not directly caused by new human activities, they are still dangerous. This calls for global cooperation in continuous monitoring and research. Such efforts are crucial for informing policy decisions and ensuring the protection of human health and the environment from mercury pollution. The Minamata Convention emphasizes the importance of research and monitoring to assess the effectiveness of measures taken to reduce emissions.
