Mercury released into the atmosphere by mainly thermic industrial processes is transported via different ways to the sea where it enters the marine food web. Now a study directed by the University of Basel has revealed how the harmful pollutant is transported to the sea in the first place. The main path is not primarily via rainfall, as previously assumed, but rather also involves gas exchange as an important process. Measures to reduce mercury emissions could therefore take effect faster than previously thought.
Mercury emissions to the atmosphere by human activities such as coal power plant operation, waste incineration or cement production outweighs natural emissions five- to tenfold.
Every year, about 2000 tons of gaseous mercury are released into the atmosphere by such activities. The harmful substance than is partly transformed to various species as it circulates between the air, soil and water in a complex biogeochemical cycle. Reaching finally the sea, it gets particularly dangerous, entering the marine food web where it accumulates in fish in the form of methylmercury. Human exposure is mainly via the consumption of contaminated fish, creating adverse effects on brain development in children or causing cardiovascular diseases in adults.
The knowledge about the transfer of mercury from the atmosphere to the sea is somehow limited, since there are no collector stations for precipitation over the sea. However, experts assumed that atmospheric mercury entered the ocean primarily via rainfall.
Photo: Rain over the sea (Photo by Auro Queiroz from FreeImages)The new study:
Now a team of researchers from University of Basel, Aix-Marseille University and Paul Sabatier University, Toulouse aimed at closing this knowledge gap. They did this by analyzing seawater samples using the technique known as fingerprinting that is based on the measurement of the distribution of the different mercury isotopes. By using the tiny weight differences between the naturally occuring mercury isotopes, the researchers can distinguish whether mercury in the seawater originates from precipitation or entered the sea via gas exchange.
For collecting the samples, the researchers embarked on several boat trips on the Mediterranean Sea 20 km offshore of Marseille. 20-L water samples were collected at depth ranging up to 1,400 m. Additional data was obtained from samples collected by research vessels in the North Atlantic.
The analyses revealed that - contrary to previous assumptions - only about half of the mercury present in the sea originates from precipitation , while the other half enters the ocean due to the uptake of gaseous mercury.
"At present, the contribution due to precipitation is probably overestimated,” says the lead author 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. The original publication
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.”
Martin Jiskra, Lars-Eric Heimbürger-Boavida, Marie-Maëlle Desgranges, Mariia V. Petrova, Aurélie Dufour, Beatriz Ferreira-Araujo, Jérémy Masbou, Jérôme Chmeleff, Melilotus Thyssen, David Point, Jeroen E. Sonke, Mercury stable isotopes constrain atmospheric sources to the ocean,
Nature, 597 (2021) 678-682. DOI: 10.1038/s41586-021-03859-8
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Related EVISA Resources October 13, 2017: Seabass populations can be differentiated by their Mercury Isotope Distribution
January 29, 2017: Toxic Mercury in Aquatic Life Could Spike due to Climate Change January 14, 2013: Mercury Levels in Humans and Fish Around the World Regularly Exceed Health Advisory Levels June 17, 2012: Factors Affecting Methylmercury Accumulation in the Food Chain
December 21, 2011: Tracing the source of mercury pollution June 28, 2010: New Study Examines Why Mercury is More Dangerous in Oceans August 21, 2009: USGS Study Reveals Mercury Contamination in Fish Nationwide May 3, 2009: Ocean mercury on the rise February 11, 2009: Mercury in Fish is a Global Health Concern October 9, 2006: Linking atmospheric mercury to methylmercury in fish February 9, 2006: Study show high levels of mercury in women related to fish consumption
last time modified: October 10, 2021