Mercury Emissions in China: Progress, Challenges, and the Role of Urban Reservoirs
China has made substantial strides in improving air quality and reducing environmental mercury (Hg) pollution in recent years. Following the enactment of the Clean Air Action plan and participation in the global Minamata Convention on Mercury – an international treaty designed to protect human health and the surroundings from anthropogenic releases of this toxic metal – atmospheric mercury concentrations across the nation have decreased by roughly 39% (1).this positive shift is largely attributable to stringent controls placed on industrial emissions, specifically targeting coal-fired power generation facilities and industrial boilers situated in densely populated urban centers (2). Though, emerging research indicates that mercury released from surface reservoirs, and notably urban soils, presents a potential obstacle to sustaining these gains.
The Impact of Policy and Industrial Regulation
the chinese government’s commitment to environmental remediation, particularly as the early 2010s, has been pivotal in curbing mercury emissions. Prior to these initiatives, coal combustion was a dominant source of atmospheric mercury, with power plants and industrial facilities contributing the vast majority of releases. The implementation of advanced pollution control technologies - such as flue gas desulfurization (FGD) systems coupled with activated carbon injection – in these sectors has demonstrably lowered direct emissions.
According to a report released by the Ministry of Ecology and environment in November 2024, the average mercury concentration in ambient air across 337 major Chinese cities decreased by 15% between 2020 and 2024. This betterment aligns with the goals outlined in the 14th Five-Year Plan (2021-2025),which prioritizes ecological conservation and pollution reduction.However, the success of these top-down regulations hinges on continued enforcement and the proactive addressing of secondary sources of mercury.
urban Reservoirs: A Hidden Source of Mercury Re-emission
While industrial controls have effectively reduced direct emissions, the focus is now shifting to understanding and mitigating mercury’s behavior within the environment. Surface reservoirs, including rivers, lakes, and crucially, urban soils, are increasingly recognized as significant sources of mercury re-emission.
urban soils, in particular, accumulate mercury through atmospheric deposition from historical industrial activity, vehicle emissions, and the use of mercury-containing products. This accumulated mercury can undergo various transformations, including methylation - a process that converts inorganic mercury into methylmercury, a highly toxic form that bioaccumulates in the food chain.
“The long-term storage capacity of mercury in urban soils represents a substantial, yet frequently enough overlooked, environmental risk.Changes in land use,soil disturbance,and climate factors can trigger the re-release of this stored mercury,potentially negating the benefits of emission control measures.”
recent investigations conducted by the Research Institute of Environmental Sciences in Beijing have revealed that mercury concentrations in some urban soils exceed permissible levels by a factor of five. This is particularly concerning in older industrial areas and near historically contaminated sites.
The Role of Methylation and Bioaccumulation
The change of inorganic mercury into methylmercury is a critical process driving environmental risk. Methylmercury is far more readily absorbed by organisms and accumulates in tissues, leading to biomagnification – the increasing concentration of a substance as it moves up the food chain.This poses a significant threat to aquatic ecosystems and human health, particularly through the consumption of contaminated fish.
A study published in Environmental Science & Technology in October 2024 demonstrated a strong correlation between methylation rates in urban soils and proximity to historical industrial sites. The researchers found that soils with higher organic matter content and anaerobic conditions (often found in waterlogged areas) exhibited the highest methylation rates. This highlights the importance of managing soil conditions to minimize mercury transformation.
Addressing the Challenge: A Multi-faceted Approach
Mitigating mercury re-emission from urban reservoirs requires a comprehensive and integrated strategy. This includes:
* Soil Remediation: Implementing targeted soil remediation techniques, such as stabilization or phytoremediation (using plants to absorb contaminants), in heavily contaminated areas.
* Stormwater Management: Improving stormwater management practices to reduce runoff and prevent the mobilization of mercury-laden sediments.
* Land Use Planning: Incorporating mercury considerations into
