Environmental Engineering Reference
In-Depth Information
gical sources, and the rest (60%) is from reemissions of previously released mercury that
has built up over decades and centuries in surface soils and oceans.
Most of the anthropogenic mercury found in the Arctic has originated from emission
sources in mid-latitudes. Historically, this was from industrial Eurasia and North America,
but the 2013 UNEP
Global Mercury Assessment
concludes that about 40% of all global
anthropogenic atmospheric emissions now comes from East and Southeast Asia. China
alone is thought to be responsible for about one-third of the global total. The same report
also showed that artisanal and small-scale gold mining in South America and Sub-Saharan
Africa is responsible for a greater proportion of global emissions than was previously be-
lieved. Back trajectory analysis (a technique we met in the context of transport of POPs)
has shown pulses of mercury being imported to the Arctic from these areas. Although
reductions in emissions since the 1950s and 1970s have been achieved in the European
Union, countries of the former Soviet Union and North America, they are being offset by
increased emissions from elsewhere, particularly Southeast and East Asia. This is consist-
ent with the results from a number of regional and global air-monitoring programmes that
allow us to detect regional trends in atmospheric concentrations. For example, from the re-
port, we can see that in parts of Western Europe, atmospheric levels have been declining
by 1.4-1.8% per year over the period 1996-2011, presumably reflecting reduced region-
al emissions. In North America, the Mercury Deposition Network and the Canadian Air
and Precipitation Monitoring Network suggest a decrease of 2.2%-17.4% in rural levels
between 1995 and 2005. Mercury levels in Mediterranean seawater have shown a decrease
between 1990 and 2004 and a similar trend has been seen in the North Atlantic. Taken to-
gether, it appears that air and surface oceanic levels of mercury have been falling, while
the mercury emissions in North America and Europe have declined from their peak values
of the mid-twentieth century. In the Pacific Ocean, levels are increasing, presumably in re-
sponse to the increasing emissions from East and Southeast Asia.
Thenetresult ofhumankind's “overloading” ofthenatural cycling mechanism ofmer-
cury has been the accumulation of increasing concentrations in surface soils, aquatic sed-
iments and the oceans. In the oceans, the mercury loading in the upper 100 metres has
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