How mercury gets into the sea

Date:
September 29, 2021
Source:
University of Basel
Summary:
Mercury released into the atmosphere by industry enters the sea
and from there makes its way into the food chain. Now, an analysis
by the University of Basel has revealed how the harmful substance
enters seawater in the first place. This is not primarily via
rainfall, as previously assumed, but rather also involves gas
exchange. Measures to reduce mercury emissions could therefore
take effect faster than previously thought.



FULL STORY ========================================================================== Mercury released into the atmosphere by industry enters the sea and
from there makes its way into the food chain. Now, an analysis by the University of Basel has revealed how the harmful substance enters seawater
in the first place. This is not primarily via rainfall, as previously
assumed, but rather also involves gas exchange. Measures to reduce mercury emissions could therefore take effect faster than previously thought.


========================================================================== Every year, 2,000 metric tons of gaseous mercury are released into the atmosphere by coal-fired power stations and mining activities. The harmful substance then adopts various chemical forms as it circulates between
the air, soil and water in a complex cycle. Mercury is particularly
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 brain development in children and cause cardiovascular diseases in adults.

"It's estimated that human activities have tripled the amount of mercury
in the surface ocean since the onset of industrialization," says the biogeochemist Martin Jiskra from the Department of Environmental Sciences
at the University of Basel. Previously, experts assumed that mercury
entered the ocean primarily via rainfall. "Those are just assumptions,
however, as there are no collector stations for precipitation over
the sea." Chemical fingerprint reveals origin As Jiskra reports in a
study published in the journal Nature, he has now closed this knowledge
gap in collaboration with colleagues from Aix-Marseille University,
Paul Sabatier University Toulouse, and the French National Centre for Scientific Research (CNRS). He did this by analyzing seawater samples
using a new method that allows researchers to distinguish whether mercury originates from precipitation or entered the sea via gas exchange. Known
as "fingerprinting," this technique is based on the measurement of
tiny weight differences between naturally occurring mercury atoms,
known as isotopes.

To collect the samples, Jiskra embarked on several boat trips on
the Mediterranean Sea, where he collected a series of 20-liter
water samples at depths ranging up to 1,400 meters off the coast
of Marseille. Additional data was obtained from samples collected by
research vessels in the North Atlantic.

Gaining a better understanding of the mercury cycle The analyses revealed
that -- contrary to previous assumptions -- only about half of the
mercury in the sea originates from precipitation, while the other half
enters the oceans due to the uptake of gaseous mercury. "At present, the contribution due to precipitation is probably overestimated," says Jiskra.

Instead, he suspects that mercury uptake by plants drives more of the
heavy metal to be deposited on land, where it is safely sequestered in
soils and poses less of a risk to humans.

Jiskra adds that the new findings are also important for the
implementation of the Minamata Convention of 2013, whereby
133 countries committed to reducing mercury emissions: "If less
mercury enters the sea via rainfall, a reduction in emissions could
cause mercury levels in seawater to drop faster than anticipated." ========================================================================== Story Source: Materials provided by University_of_Basel. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Martin Jiskra, Lars-Eric Heimbu"rger-Boavida, Marie-Mae"lle
Desgranges,
Mariia V. Petrova, Aure'lie Dufour, Beatriz Ferreira-Araujo,
Je're'my Masbou, Je'ro^me Chmeleff, Melilotus Thyssen, David Point,
Jeroen E.

Sonke. Mercury stable isotopes constrain atmospheric sources to the
ocean. Nature, 2021; 597 (7878): 678 DOI: 10.1038/s41586-021-03859-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210929124357.htm

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