Arsenic, a toxic element from human-made and natural sources, enters the environment through air circulation and deposition (both dry and wet). Biomethylation turns Arsenic into a gas, which then cycles back to the surface, impacting soil and plants.
Understanding the chemical forms of Arsenic that land on the surface is key to knowing how it behaves in soils and affects organisms. However, how arsenic species travel in the atmosphere and their sources have been poorly studied.
Researchers from ETH Zurich analyzed particulate matter, clouds, and rainwater for arsenic traces on Pic du Midi in the Pyrenees. Using new measurement techniques, they have uncovered the transport pathways of this environmental toxin in the atmosphere.
The researchers conducted an extensive measurement campaign at the Pic du Midi research station, located 2,877 meters above sea level, where measurements are mostly unaffected by local pollution sources.
At the Pic du Midi, they found that clouds contain significantly more Arsenic on average than rainwater. However, there’s no need to worry about being poisoned by the next rainfall.
Lenny Winkel, a Professor at the Institute of Biogeochemistry and Pollutant Dynamics at ETH Zurich, said, “The Arsenic is very diluted in the atmosphere. The researchers had to optimize their measurement method to detect Arsenic. The measurement limit is now 1 to 2 nanograms per liter, up to twenty times lower than the measurement limit of previous methods.”
Using a sophisticated model of air mass movements and chemical analyses of cloud and rainwater, the researchers identified different transport patterns of Arsenic. By examining the composition of each sample, they could trace the source of the Arsenic. For example, if a sample had high sodium levels, they concluded that the Arsenic had likely mixed with sea salt (sodium chloride) during its journey to the Pyrenees.
Esther Breuninger, the first author of the scientific paper, said, “We found dissolved organic carbon in other samples. It can come from natural sources such as plants and pollen. But it can also be due to human-induced environmental pollution from transport or industry.”
“In any case, the dissolved organic carbon indicates that the arsenic must have traveled over land masses before it ended up in our sample.”
The team found arsenic in the rainwater samples and so-called methylated arsenic compounds. These compounds form when bacteria, algae, plants, or fungi absorb inorganic Arsenic and then release it in a converted form, potentially to protect themselves. The researchers’ analyses revealed that Arsenic undergoes conversion both in the sea and on land.
Winkel said, “Until now, it was assumed that human activities such as burning coal or smelting ores were mainly responsible for atmospheric Arsenic. However, in some cloud samples, methylated compounds comprised most of the Arsenic detected. These results show that biological processes are more important than previously assumed.”
“Now, the influence of biological processes on the global arsenic cycle needs to be considered more in the models. Living organisms contribute to mobilizing historical arsenic pollution and its global distribution through their metabolism.”
Journal Reference:
- Breuninger ES, Tolu J, Aemisegger F, Turnherr I, Bouchet S, Mestrot A, Ossola R, McNeill K, Tukhmetova D, Vogl J, Meermann B, Sonke JE, Winkel LHE. Marine and terrestrial contributions to atmospheric deposition fluxes of methylated arsenic species. Nature Communications 2024. 15: 9623, DOI: 10.1038/s41467-024-53974-zcal
