Fjölrit RALA - 15.06.2004, Blaðsíða 130

Mercury accumulation in European volcanic soils with special reference to
the role of the properties of andic horizons
J.C. Nóvoa; X. Pontevedra; A. Martínez-Cortizas and E. García-Rodeja
Dep. de Edafoloxía e Q. Agrícola, Fac. Bioloxía, Univ. de Santiago de Compostela. Galicia, Espana.
Mercury is considered to be a global pollutant due to its ability to undergo long distance
transportation in the atmosphere and because is able to promote adverse effects on
environment and human health. Volcanoes represent a significant natural source of Hg in the
atmosphere and some estimates range from 20 to 2000 t of Hg per year for global flux (Nriagu
& Becker, 2003). Mercury emitted from volcanoes reaches the atmosphere through
cataclysmic eruptions, supplying enough volatile Hg to change the global and regional cycle
of Hg in a few years (Coffey, 1996), and through passive degassing and moderate eruptions
which can have long-term effects on the local environments. In both cases volcanogenic Hg
can readily enter into the ecosystem and thus, can constitute a hazard to the environment and
to human health.
More than 90% of the released Hg enters the terrestrial ecosystems (Lindqvist et al., 1991)
being the soils the largest Hg sink. Nevertheless, the Hg content of volcanic soils cannot be
used as an indirect estimate of the amount of Hg emitted for volcanoes. Hg accumulation in
volcanic soils results from complexes interactions between atmospheric deposition, soil
retention and Hg released from soil (Gustin et al., 2002).
In Europe, the volcanic activity is or was present in different areas like the Mediterranean
Sea (Italy and Greece), the Atlantic Ocean (Azores Islands, Portugal; Iceland and Canary
Islands, Spain) and in continental areas (France and Hungary). Twenty COST 622 reference
soil profiles (94 soil horizons) were selected in these volcanic regions to determine the total
Hg content, the degree of soil Hg accumulation using enrichment factors and the relationships
between total Hg and outstanding volcanic soil properties, in order to provide an insight on
Hg geochemistry in these soils in Europe. Mercury concentrations were measured, by
duplicate, in air dried and ground soil samples of the fine earth fraction using an LECO-
ALTEC AMA-254 Hg Analyzer (detection limit: 0,05 ng; working range: 0,05-600 ng of Hg
g 1 dry matter). Standard reference materials (NIST 1547 and NIST 1633b) were run within
each set of analysis and the values obtained were in the precision range for each standard.
Differences between soil replicates are less than 1 %.
The highest total Hg values were found in soils from Italy (profile Nl), Azores Islands
(profiles N5 and N6) and Canary Islands (profile N10). Most of the horizons of these soils
have Hg concentrations above 200 ng g"1 of dry soil. The lowest values were measured in
horizons from Iceland (N7, N8 and N9), Greece (N13, N14 and N14a) and Hungary (N17,
N18 and N19) soils, for which total Hg content is below to 100 ng g'1 of dry soil. These
results show that a clear trend between total soil Hg content and the volcanic activity for
different geographical areas (Atlantic Ocean, Mediterranean basin or continental Europe)
cannot be established.
Regarding to Hg content, some of the horizons presented values higher than those recently
published by Tomiyasu et al (2003) for Japanese volcanic soils, although most of them are in
the range published by these authors (6.5-229 ng g"1 dry matter).
Vertical profiles of total Hg in the soils revealed a strong Hg accumulation in the upper
horizons (O and A horizons). This trend in Hg distribution with depth is probably associated
to soil organic matter, which has been considered a strong Hg adsorbant (Lindqvist, 1991;
Tomiyasu et al., 2003).
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