Nature
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Researchers at ETH Zurich have found traces of arsenic in particulate matter, clouds, and rainwater. Using new optimized measurement techniques, they have identified various ways that the toxic substance is transported into the atmosphere. Among these is a surprising route that involves previously underappreciated biological processes.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.Arsenic is a naturally occurring but highly toxic element that is classified as a Group 1 carcinogen – meaning there is enough evidence to demonstrate it can cause cancer – by the International Agency for Research and Cancer (IARC).
For years, Lenny Winkel, a professor at the Institute of Biogeochemistry and Pollutant Dynamics at ETH Zurich, and colleagues have been exploring the presence of this element in the atmosphere. Although arsenic is widely distributed across the Earth’s crust, it is also present in the air, on land, and in water. At present, it is estimated that around 31 tonnes of it is in the atmosphere, the majority of which has been put there by human activity – from minding, landfills, and the burning of fossil fuels that produce inorganic arsenic.
However, air pollution controls introduced to North America and Europe during the last few decades have led to a decrease in the amount of arsenic emissions being produced. Still, the long-term effects of it in the atmosphere remain a concern and need monitoring.
During their latest research, Winkel and colleagues carried out extensive measurements at the Pic du Midi research station located 2,877 meters (9,439 feet) above sea level in the Pyrenees mountains. At this height, it becomes possible for researchers to examine arsenic in the atmosphere without worrying about the influence of local sources of pollution.
The team found that, on average, the clouds surrounding Pic du Midi contained significantly higher levels of arsenic on average than rainwater. But while this may be an alarming result, it is not likely enough to cause individuals any harm.
“The arsenic is very diluted in the atmosphere,” Winkel explained in a statement. The level is so low, in fact, that the researchers had to adjust their measurements to detect it.
So how is this lower level of arsenic getting into the atmosphere? The team created a model of air mass movement and conducted an analysis of clouds and rainwater, which led to a range of transport patterns being identified. This allowed them to figure out where the arsenic in each sample came from.
For example, for samples that contained large amounts of sodium, the researchers believe it likely came from the sea where it was mixed up with sodium chloride as it traveled towards the Pyrenees.
They also found samples with organic carbon dissolved in them.
“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,” Esther Breuninger, the first author of the team’s new paper added.
"In any case, the dissolved organic carbon indicates that the arsenic must have travelled over land masses before it ended up in our sample."
In addition, the team found rainwater samples with methylated arsenic compounds in them. These compounds are produced when organisms like bacteria, algae, plants, or fungi absorb inorganic arsenic and then excrete it in an organic form. The new research indicates that this conversion takes place in both the sea and on land.
"Until now, it was assumed that human activities such as the burning of coal or the smelting of ores were mainly responsible for atmospheric arsenic," said Winkel. However, in some cloud samples, methylated compounds made up the majority of the arsenic detected. "These results show that biological processes play a more important role than previously assumed," Winkel added, concluding that factoring this finding into future modeling will be essential.
The study is published in Nature Communications.
