Beneath the Surface: How Soil Mercury is Fueling a Climate Crisis

By Vivek Saini

In recent years, the link between mercury pollution and climate change has garnered increasing attention, with new research shedding light on how soil mercury contributes to global warming. Traditionally viewed as a toxic contaminant primarily affecting aquatic systems, mercury in soil has now emerged as a critical factor in climate dynamics. As climate change accelerates, rising temperatures and changing precipitation patterns are triggering the release of mercury from soils into the atmosphere, exacerbating global warming. This intricate relationship between mercury and climate change poses significant challenges for environmental management and public health, underscoring the need for comprehensive strategies to address both issues.

How mercury in soil is worsening climate change

Mercury, recognised for its toxicity in aquatic ecosystems, has recently been shown to have significant implications for climate change when present in soil. Soil acts as a vast reservoir for mercury, absorbing it through atmospheric deposition, plant decay, and human activities like industrial emissions. However, this mercury does not remain trapped indefinitely. Climate change, through mechanisms such as rising temperatures and altered precipitation patterns, can trigger the release of mercury from soils into the atmosphere. This release is facilitated by soil warming, which increases microbial activity and chemical reactions that volatilise mercury, converting it from a solid or liquid state into a gaseous form that quickly escapes into the atmosphere.

This atmospheric mercury then contributes to global warming by absorbing and re-emitting solar radiation, known as radiative forcing. In this way, mercury directly and indirectly contributes to climate change. The research highlights that this problem is exacerbated by vegetation greening, which is a response to warming temperatures. As plants grow more vigorously due to warmer conditions and higher carbon dioxide levels, they absorb more mercury from the atmosphere. When these plants decay, the mercury is deposited into the soil, increasing the soil’s mercury content. This cycle continues, creating a dangerous feedback loop where climate change leads to more mercury release, accelerating climate change.

“Mercury pollution in soil is a growing concern, especially concerning climate change. Increasing global temperature can volatilise the mercury accumulated in the soil, especially in the Arctic Zone, where permafrost thaw is increasing mercury release,” explains Alokya Kanungo, a PhD scholar at Kalinga Institute of Industrial Technology, while interacting with CFC India. “This will elevate the methylmercury level, which has significant ecological and health implications and potentially intensifies a feedback loop that contributes to further atmospheric warming.”

A study from MIT found that deforestation releases around 200 tons of mercury into the atmosphere annually, representing about 10% of human-made emissions. This is particularly relevant in tropical regions, where land clearing for agriculture can exacerbate mercury release from soils, compounding the effects of climate change​. Furthermore, another Environmental Science & Technology study underscores that it is not a localised problem at all. The global nature of atmospheric circulation means that mercury released from soils in one part of the world can travel vast distances, affecting ecosystems and human health far from the source. This underscores the global nature of mercury pollution, a concern that needs to be addressed alongside other climate-related issues.

The complex relation between mercury and global warming

The relationship between mercury in soil and global warming is complex. It involves a series of complex interactions between biological, chemical, and physical processes. Mercury deposited in soils can remain trapped for decades, even centuries, but changes in environmental conditions, particularly those driven by climate change, can destabilise this storage. For example, as temperatures rise, the increased soil temperatures can enhance microbial activity, converting mercury into more volatile forms that can be released into the atmosphere. This process is particularly concerning in regions with large amounts of stored mercury, such as areas with heavy industrial legacies or regions where mercury naturally accumulates in the soil.

Once mercury is released into the atmosphere, it doesn’t remain stationary. It becomes part of the global mercury cycle, where it can travel across continents, eventually depositing far from its source. This process of long-range atmospheric transport means that even remote areas can be affected by mercury pollution. For instance, mercury released in industrial regions of Asia can end up in the Arctic, posing severe risks to local wildlife and indigenous communities. Mercury contributes to global warming in the atmosphere by interacting with other greenhouse gases and atmospheric particles, further complicating the already complex climate system.

Kanungo emphasises the global priority, stating, “Globally, the priority should be given to mitigate mercury emissions from anthropogenic sources and to advance research on mercury cycling to develop effective management and remediation strategies.”

The study also underscores that while reducing mercury emissions from industrial sources is crucial, more is needed to mitigate mercury’s impact on climate change. The remobilisation of mercury from soils due to climate change represents a significant and often overlooked source of mercury emissions. This makes it essential to incorporate soil mercury management into broader climate strategies. The research calls for a more integrated approach that considers the interplay between mercury pollution and climate change, recognising that addressing one issue without considering the other may lead to unintended consequences.

The mercury-climate feedback loop

As highlighted in this study, one of the most troubling aspects of mercury pollution is the positive feedback loop it creates with climate change. This feedback loop begins with rising global temperatures, which increase the release of mercury from soils into the atmosphere. As mercury enters the atmosphere, it contributes to the greenhouse effect, which further warms the planet. This warming then releases more mercury from the soil, creating a self-perpetuating cycle that is difficult to break.

This feedback loop is particularly concerning in regions where the effects of climate change are most pronounced, such as the Arctic. In these areas, permafrost thawing releases vast amounts of mercury locked away for millennia, a phenomenon called ‘legacy mercury‘. The release of this ‘legacy mercury’ is accelerating climate change and posing significant risks to local ecosystems and human health. The study points out that even regions that have not traditionally been considered mercury hotspots are now at risk due to this feedback loop. For example, temperate areas of North America and Europe, where warming increases vegetation growth, also see rises in soil mercury levels.

The research suggests that breaking this feedback loop will require more than reducing mercury emissions. It will also require addressing the underlying drivers of climate change, such as greenhouse gas emissions, and developing strategies to manage the remobilisation of mercury from soils. This could include land-use changes, reforestation efforts, and improved pollution control technologies. Without such interventions, the mercury-climate feedback loop could continue exacerbating global warming, leading to more extreme climate impacts and significant health risks for people worldwide.

“A multifaceted approach at local and global levels can reduce the risk of mercury pollution in soil and its contribution to the climate change feedback loop,” suggests Kanungo. “Locally, mercury emissions can be reduced by practising farming methods that improve soil stability and minimise disturbances. Phytoremediation techniques can be used for mercury removal from contaminated areas.” “To understand the dynamics of mercury under climate change scenarios and to create mitigation technologies and policies, we should focus on strengthening the framework of the Minamata Convention and conducting collaborative research on a global level,” she added.

Regional Hotspots: Where Mercury Pollution Could Hit Hardest

The study identifies several regions worldwide that are particularly vulnerable to the effects of mercury pollution, both due to their environmental characteristics and exposure to climate change. One of the most significant findings is identifying temperate areas in East Asia, North Europe, and North America as potential hotspots for mercury pollution by the year 2100. In these regions, warming-induced vegetation greening is expected to lead to substantial increases in soil mercury levels, with some areas projected to see increases of over 20 ng/g. This is particularly concerning for regions with dense human populations and significant agricultural activities, where mercury can quickly enter the food chain.

The study by Guo et al. also identified the Arctic as a major hotspot. The thawing of permafrost in this region releases vast amounts of mercury stored in frozen soils for thousands of years. This release contributes to climate change and poses significant risks to local ecosystems and communities. Indigenous populations in the Arctic, who rely on local wildlife for food, are particularly vulnerable to the effects of mercury pollution. The study highlights the need for targeted interventions in this region to mitigate the impacts of mercury release and protect both human and environmental health.

In addition to the Arctic and temperate regions, the study also points to tropical areas, such as the Amazon and Central Africa, as being at risk. These regions are experiencing changes in precipitation patterns due to climate change, which can lead to increased mercury release from soils. The study suggests that increased rainfall and higher temperatures could lead to significant mercury mobilisation in some tropical areas, potentially devastating local ecosystems. Given the importance of these regions for global biodiversity and the livelihoods of millions of people, the study calls for urgent action to address mercury pollution in these hotspots.

References:

https://pubs.acs.org/doi/10.1021/acs.est.4c01923

https://phys.org/news/2024-08-mercury-pollution-soil-climate.html

https://news.mit.edu/2024/study-global-deforestation-leads-more-mercury-pollution-0212

https://www.sciencedaily.com/releases/2024/08/240814124536.htm

https://link.springer.com/article/10.1007/s00128-022-03544-0

https://link.springer.com/chapter/10.1007/978-3-030-55635-8_3

Image: https://pubs.acs.org/cms/10.1021/acs.est.4c01923/asset/images/large/es4c01923_0004.jpeg

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