How The Mercury Reaches The Sea

November 3, 2021

Mercury released into the atmosphere by industry enters the sea and from there it passes into the food chain. Now, an analysis by the University of Basel (Switzerland) has revealed how this harmful substance enters seawater.

It is not mainly through precipitation, as was supposed until now, but gas exchange also intervenes. Therefore, measures to reduce mercury emissions could take effect faster than previously thought.

Every year, coal-fired power plants and mining activities emit 2,000 tons of mercury gas into the atmosphere. The harmful substance then takes various chemical forms as it circulates between air, soil and water in a complex cycle.

Mercury is especially dangerous in the sea, where it accumulates in fish in the form of highly toxic methylmercury. When this compound enters the human body due to the consumption of fish, it can have an adverse effect on children and adults.

“It is estimated that human activities have tripled the amount of mercury on the ocean surface since the beginning of industrialization,” says biogeochemist Martin Jiskra , from the Department of Environmental Sciences at the University of Basel.

Previously, experts assumed that mercury entered the ocean primarily through precipitation. “However, they are only assumptions, since there are no rainfall collecting stations over the sea.”

The chemical fingerprint reveals the origin

As Jiskra reports in a study published in the journal  Nature , he has analyzed seawater samples with a new method that allows researchers to distinguish whether the mercury comes from precipitation or has entered the sea through gas exchange.

Known as “fingerprinting,” this technique is based on the measurement of minute differences in weight between natural mercury atoms, known as isotopes.

20-liter water samples were collected at depths of up to 1,400 meters off the coast of Marseille. Additional data was obtained from samples collected by research vessels in the North Atlantic.

Better understand the mercury cycle

The analyzes revealed that only half of the mercury present in the sea comes from rainfall. While the other half enters the oceans due to the absorption of gaseous mercury. At present, the contribution due to precipitation is probably overestimated.

It is suspected that the absorption of mercury by plants causes more of the heavy metal to be deposited in the ground, where it is sequestered safely and poses less risk to humans.

Jiskra adds that the new findings are also important for the implementation of the 2013 Minamata Convention, whereby 133 countries committed to reducing mercury emissions:

“If less mercury enters the sea through precipitation, a reduction in emissions could cause the levels of mercury in seawater to fall faster.”

Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
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