A newly identified microbial process may be secretly adding large amounts of mercury to the air every year, according to a study conducted by researchers at China’s Nankai University.
Elemental mercury (Hg⁰) is a toxic air pollutant that can travel thousands of miles and circulate around the world. For years, scientists have struggled to fully explain the levels of mercury measured in the atmosphere. Known sources such as coal burning, mining, and industrial processes do not fully explain what monitoring stations detect. Researchers suspect they are missing a key source of information.
A new study points to an unexpected culprit: microorganisms that feed on small mineral particles containing mercury.
Mercury often exists in the environment as mercury sulfide, and mercury sulfide has long been thought to be a chemically stable and relatively immobile mineral. However, the researchers found that mercury sulfide behaves very differently when formed as very small particles, one billionth of a meter in size.
Scientists have shown in laboratory experiments that certain chemoautotrophic microorganisms (organisms that obtain energy by oxidizing inorganic compounds) can use mercury sulfide nanoparticles as their sole energy source. These included sulfur-oxidizing microorganisms and iron-oxidizing microorganisms.
When microorganisms break down nanoparticles to promote growth, elemental mercury (Hg⁰) is released. Mercury is a volatile substance that escapes into the atmosphere, spreads throughout the Earth, and eventually returns to ecosystems. Here it can be converted to methylmercury. Methylmercury is a powerful neurotoxin that accumulates in fish and poses a serious risk to human health.
Particle size appears to be important. The researchers found that nanoscale mercury sulfide particles can enter microbial cells more easily than dissolved forms of mercury, which typically require tightly controlled uptake systems. Once inside cells, minerals are broken down by microbial metabolism. The mercury is then converted to elemental mercury and released.
In other words, microbes are not only interacting with mercury in the soil, but may also be actively converting it into a form that can re-enter the atmosphere.
To understand how important this process is beyond the laboratory, the team combined experimental data with global information on soil, nanomineral presence, and microbial activity.
They estimate that this microbial mechanism could release approximately 272 ± 135 tons of elemental mercury per year worldwide, a figure comparable to emissions from global cement production, which is currently the fourth largest source of man-made mercury in the world.
If accurate, this finding means that natural soil processes involving nanoparticles and microorganisms may be a previously overlooked but important component of the global mercury cycle.
The authors say the results highlight the need to rethink how mercury moves through the environment. Current emissions inventories and atmospheric models may not take into account interactions between nanominerals and microorganisms, especially in soils and other environments where chemoautotrophic microorganisms thrive.
Incorporating this newly identified pathway could allow scientists to better explain mercury levels in the atmosphere and improve predictions about how mercury pollution will respond to environmental change.
The discovery adds further complexity to the global mercury cycle, suggesting that even the smallest particles can act through microscopic life forms and affect the entire planet.
complete research You can read it here.
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