Elemental mercury (Hg 0 ) is a toxic air pollutant that can travel long distances and circulate globally. Scientists have long suspected that today’s emission inventories do not fully explain measured mercury levels in the atmosphere, pointing to missing sources.
Now, a study published in National Science Review reports a previously overlooked natural mechanism that could contribute substantially to global mercury emissions. The researchers show that chemolithoautotrophic microbes can use mercury sulfide nanominerals as an energy source and, in the process, release volatile Hg 0 into the air.
“Mercury sulfide is often considered chemically stable in the environment,” the authors note, “but when it exists as nanoparticle, it becomes much more accessible to microbes.” In laboratory experiments, the team found that representative sulfur-oxidizing and iron-oxidizing microbes could grow with mercury sulfide nanoparticles as their sole energy source while producing substantial Hg 0 .
Particle size plays a key role. The study suggests that nanoscale mercury sulfide particles can enter microbial cells more readily than dissolved mercury species, which typically require tightly controlled uptake. Once inside the cell, microbial metabolism breaks down the mineral, releasing mercury that is ultimately converted into Hg 0 and emitted into the atmosphere.
To assess how important this pathway could be at the global scale, the researchers combined experimental results with global information on soils, nanomineral occurrence, and microbial activity. Their estimate suggests that this nanomineral-driven microbial process could release approximately 272 ± 135 tonnes of Hg 0 per year, comparable to mercury emissions from cement production, which is currently ranked as the world’s fourth-largest anthropogenic mercury source.
The authors say the findings highlight a missing but potentially significant component of the mercury cycle, and that future mercury budgets and atmospheric models should consider nanomineral–microbe interactions, especially in environments where chemolithoautotrophic microbes thrive.
National Science Review
Experimental study