New Microbial Pathway Identified as Major Source of Atmospheric Mercury

A study conducted by researchers at Nankai University in China has identified a microbial process that may contribute significant amounts of mercury to the air annually.

This newly recognized mechanism could help explain previously unaccounted-for levels of atmospheric mercury.

Elemental mercury (Hg 0) is a toxic air pollutant known for its global travel. While current known sources, such as coal burning, mining, and industrial processes, contribute significantly, they do not fully explain detected atmospheric mercury levels, leading scientists to suspect an important missing source.

Microbial Mechanism

The study reveals a novel interaction where microbes consume tiny mineral particles containing mercury. Notably, mercury sulfide, typically considered chemically stable, behaves differently when present as nanoparticles (billionths of a meter).

Laboratory experiments successfully demonstrated that certain chemolithoautotrophic microbes, specifically sulfur-oxidizing and iron-oxidizing types, can utilize these mercury sulfide nanoparticles as their sole energy source. As these microbes metabolically break down the nanoparticles for growth, they actively release elemental mercury (Hg 0).

This volatile form of mercury can then readily escape into the atmosphere, spread globally, and eventually settle back into various ecosystems. Once in these environments, it can convert into methylmercury—a potent neurotoxin that bioaccumulates in fish and consequently poses significant health risks to humans.

Particle size is a critical factor in this process; nanoscale mercury sulfide particles are able to enter microbial cells more readily than dissolved forms. Once inside, the powerful microbial metabolism effectively breaks down the mineral, transforming the mercury into its elemental form for subsequent release.

Estimated Global Impact

To assess the importance of this process beyond the controlled environment of the laboratory, researchers meticulously combined experimental data with extensive global information on soils, nanomineral occurrence, and microbial activity. Their comprehensive estimate suggests that this newly identified microbe-driven mechanism could release approximately 272 ± 135 tonnes of elemental mercury per year worldwide.

This significant figure is comparable to emissions from global cement production, which is currently ranked as the fourth-largest human-made source of mercury.

If these findings are accurate, they indicate that natural soil processes involving nanoparticles and microbes represent a substantial, previously overlooked component of the global mercury cycle. The results strongly suggest a critical need to re-evaluate how mercury moves through the environment. Current emission inventories and atmospheric models may not adequately account for these nanomineral–microbe interactions, especially in soils and other environments rich in chemolithoautotrophic microbes.

Incorporating this newly identified pathway into future models could enable scientists to better explain existing atmospheric mercury levels and significantly improve predictions regarding mercury pollution's response to environmental changes. This discovery undeniably adds another layer of complexity to the global mercury cycle, powerfully highlighting that even microscopic particles and life forms can exert planet-wide effects.