In 2017, the Minamata Convention on Mercury was implemented to help reduce mercury emissions and limit exposure worldwide. However, a recent study analyzing mercury levels in soil indicates that the measures outlined in the treaty might fall short. This research, published in ACS’ Environmental Science & Technology, suggests that soil holds significantly more mercury than previously believed, and it warns that climate change-driven increases in plant growth could further elevate these levels.
In 2017, the Minamata Convention on Mercury was implemented to help reduce mercury emissions and limit exposure worldwide. However, a recent study analyzing mercury levels in soil indicates that the measures outlined in the treaty might fall short. This research published in ACS’ Environmental Science & Technology suggests that soil holds significantly more mercury than previously believed, and it warns that climate change-driven increases in plant growth could further elevate these levels.
Mercury is a long-lasting environmental contaminant that travels through the air, water, and soil, building up in plants and animals. Soil acts as the main reservoir for mercury, retaining three times more than what is found in oceans and 150 times more than in the atmosphere. Under normal conditions, this heavy metal cycles naturally through various reservoirs, but human activities have disrupted this process. Climate change, driven by human actions, increases carbon dioxide levels, encouraging plant growth which likely leads to more mercury deposits in the soil as plant matter decomposes. While earlier studies focused on mercury levels in specific regions, researchers Xuejun Wang, Maodian Liu, and their team sought to create a more comprehensive global model that accounts for the warming climate’s impacts on soil mercury levels.
The researchers gathered nearly 19,000 previous soil mercury measurements, assembling one of the most extensive databases on this topic. They applied machine learning techniques to estimate the global distribution of mercury in both topsoil and subsoil. Their findings reveal that approximately 4.7 million tons of mercury are stored within the first 40 inches (about 1 meter) of soil, which is double prior estimates, though some earlier analyses considered a shallower soil depth. Their model showed the highest mercury concentrations in densely vegetated regions, particularly in low tropical latitudes, along with areas of permafrost and regions with high human populations. In contrast, areas with sparse vegetation, such as shrublands or grasslands, displayed significantly lower soil mercury levels.
To determine the potential effects of climate warming on mercury levels in soil, the researchers integrated their initial model with environmental datasets that reflect future climate scenarios. Their projections suggest that as global temperatures rise, increased vegetation growth could lead to elevated mercury levels in the soil. This interconnected effect could surpass the reductions anticipated from current global initiatives, including those set out in the Minamata Convention. While further research and monitoring are required, the study highlights the urgent need for more stringent, long-term strategies to manage both mercury and carbon dioxide emissions simultaneously.
