The amount of
mercury near the surface of many of the world’s
oceans
has tripled as the result of our polluting activities, a new study has
found, with potentially damaging implications for marine life as the
result of the accumulation of the
toxic metal.
Mercury
is accumulating in the surface layers of the seas faster than in the
deep ocean, as we pour the element into the atmosphere and seas from a
variety of sources, including mines,
coal-fired power plants
and sewage.
Mercury is toxic to humans and marine life, and accumulates
in our bodies over time as we are exposed to sources of it.
A sewage drain floods into the Mediterranean Sea off the coast of Gaza, in Nuseirat.
Photograph: Warrick Page/Getty Images
Since the industrial revolution, we have tripled the mercury content of shallow ocean layers, according to the
letter published in the peer-review journal Nature on Thursday.
Mercury can be widely dispersed across the globe when it is deposited
in water and the air, the authors said, so even parts of the globe
remote from industrial sources can quickly suffer elevated levels of the
toxic material.
Mercury in the open ocean : sources to seafood
For several years, scientists have warned that pregnant women and small children should
limit their consumption of certain fish,
including swordfish and king mackerel, because toxic metals including
mercury and lead have been accumulating in these species to a degree
that made their over-consumption dangerous to human health.
Pregnant
women are particularly at risk because the metals can accumulate in the
growing foetus, and in sufficient quantities can cause serious
developmental disorders.
Environment officials are in Geneva to work out a new treaty to cut mercury levels in the ocean. The United Nations says mercury in the world's oceans has doubled over the past century, causing serious health concerns. (Jan 2013)
The scientists behind Thursday’s letter to
Nature, including researchers from the prestigious
Woods Hole Oceanographic Institution
in the US, stopped short of warning on the dangers to human health from
our pouring of mercury into the oceans.
However, they said, further
research could yield more advice on the potential impacts: “This
information may aid our understanding of the processes and the depths at
which inorganic mercury species are converted into toxic methyl mercury
and subsequently bioaccumulated in marine food webs.”
Styrofoam models of dead fish placed by Greenpeace environmental activists float near a ship moored in Argentina's most polluted river, the heavy-metal laced, reeking Riachuelo, November 28, 2000.
Simon Boxall,
lecturer on ocean and Earth science at the University of Southampton,
said it was “hard to say” from the research how much damage had already
been done to marine life, including edible fish species, and how quickly
any such damage would become apparent.
“I would not stop eating ocean
fish as a result of this,” he said.
“But it is a good indicator of how
much impact we are having on the marine environment. It is an alarm call
for the future.
GeoTraces is an international programme which aims to improve the understanding of biogeochemical cycles and large-scale distribution of trace elements and their isotopes in the marine environment.
Deep waters in the North Atlantic showed more
mercury content than similarly deep waters of the South Atlantic and the
Southern and Pacific Oceans, the authors of the report said.
Mercury at
the surface will disperse to lower layers in time, but this can take
decades.
However, the process of the damage to marine life becoming
apparent can be faster in some areas, such as those closer to the poles,
than areas nearer the equator, said Dr Boxall.
Mercury in fish
The north pole and the Arctic circle, because of the winds and ocean currents, is an area where
many pollutants released elsewhere across the globe accumulate:
top predators such as polar bears have been found to have high levels
of toxins in their bodies as a result.
These animals are sometimes eaten
by indigenous Arctic peoples.
“In the Arctic and Antarctic, you
will be starting to see some of this now,” he said.
“But with deep-sea
fishing in the tropics you will not see it yet, but you will see it
within a hundred years.”
Mercury emissions from coal-fired power plants
can be reduced by using chemical filters, but while this is
increasingly the norm in the rich world many developing countries have
yet to catch up. Another source of the metal is from sewage.
Developed
countries have means to reduce this impact, but again developing
countries are less likely to have in place the treatment systems
necessary.
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