|Characterisation Method Name:|
|Hg air emissions impact on NEX|
|Principal Method Name:|
|EPS: empirical method|
|NEX is Normalised EXtinction of species.|
The characterisation factor is determined by the empirical method.
Category indicator value in system considered
Hg’s impact on bio-diversity is perhaps the most difficult part to evaluate The global
threat to bio-diversity is only to a small part coming from mercury. In Sweden the Fauna
Preservation Committee estimated (1988) that 13 out of 140 NEX was in danger because
of toxic substances in the environment. The best knowns of these are PCB, DDT and
mercury. A rough guess is that 1% of the NEX on the globe are threatened by mercury.
Contribution to category indicators value from a flow unit
The global anthropogenic emission of Hg is estimated to 8600 tons per year (UNEP, 1992) and the bio-geochemical is around 70000 ton (Fergusson, 1989). The atmosphere is the main transport route for mercury and the run-off from the lithosphere to the oceans is
only 3800 – 5000 ton compared to the mercury from precipitation, 25000 ton annually.
Totally the emissions contributing to the population exposure via fish is 8600 + 70000 + 4600 = 83200 ton.
Calculation of characterisation factor
The characterisation factor is thus 0.01/83200000 = 1.20E-10 /kg Hg.
|1. UNEP Environmental data report 1991/92 p. 36, 1992. 2. Fergusson, J.E., “The heavy elements: Chemistry, Environmental Impact and Health Effects”, Pergamon Press, Oxford, 1990.|
|Having the global extension of the emission flow group, there will also be a global extension of the environment system. The time borders may be considerable as Hg has a tendency to "move around" in the environment. After having been deposited it may be re-emitted again as it may be chemically transformed from volatile to non-volatile compounds. The knowledge about these processes is however very limited as far as quantitative aspects are concerned. We therefore assume a "steady state" and make the analysis on one-year basis. The reference year will be the same as for emissions, 1985.|
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