Much mercury enters the oceans via atmospheric gas exchange. (Image: Keystone)
Basel
Contrary to what was previously assumed, only about half of the mercury reaches the seas through rain. This is what a Basel research team reports.
The oceans swallow just as large a portion via atmospheric gas exchange as a team by a Basel researcher reported on Wednesday in the specialist magazine “Nature” .
Mercury is a neurotoxin that enters the body primarily through the consumption of seafood and fish. The organisms accumulate the heavy metal in their tissues in the form of highly toxic methylmercury.
The biogeochemist Martin Jiskra and his French colleagues have now used isotopes to investigate the routes through which mercury enters the oceans . Their conclusion: “The contribution of precipitation is currently probably overestimated,” said the researcher according to a communication from the University of Basel.
Instead, the gas exchange at the air-water boundary plays a much larger role than previous Earth system models would suggest. The entry from rain has so far been difficult to quantify because “there are no collecting stations for precipitation above the sea”, says Jiskra.
Both entries equally important
The team analyzed samples from the Mediterranean and the North Atlantic that contained water from a depth of 1400 meters. According to this, 42 percent of the mercury got into the oceans through rain, 58 percent through gas exchange. On the basis of this data, the researchers estimated that, on a global basis, the input from rain and gas exchange is balanced at 50 percent each.
According to Jiskra, human activities have estimated the amount of mercury in the surface ocean since the beginning tripled during industrialization – especially through coal-fired power stations and mining.
Plants absorb more mercury
The newly gained knowledge is encouraging, because: «A low entry of mercury through rain means that the mercury has to be dumped elsewhere, since globally speaking the emissions and Keeping entries in balance, ”Jiskra told the Keystone-SDA news agency.
New findings indicate that more mercury than previously thought is deposited on land and stored in the soil through plant uptake. This means that anthropogenic mercury emissions are stably bound in soils relatively quickly and withdrawn from the global cycle. A reduction in emissions could therefore lead to a faster decline in the mercury concentration in the atmosphere and also in the sea than previously assumed.
In 2013, 133 states signed up to the Minamata Convention obliged to reduce mercury emissions.
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