Programa e Resumos - I Congresso Ibérico de Ciência do Solo 2004

I Congresso Ibérico da Ciência do Solo – 15 a 18 de Junho de 2004, Bragança, Portugal
Total Hg content in acid forest soils nearby a coal-fired power-plant in
Galicia (NW Spain).
1 Nóvoa-Muñoz, Juan Carlos; Pontevedra-Pombal, Xabier; Martínez-Cortizas, Antonio &
Eduardo García-Rodeja.
1 Dpto. Edafología y Química Agrícola. Fac. Biología. Universidad de Santiago de Compostela.
Rúa Lope Gómez de Marzoa s/n, 15782 Santiago de Compostela, Galicia, España.
Resumo
Comunicação: Painel
Total Hg contents were measured in five soil profiles, nearby a coal-fired power plant
located in Galicia (NW Spain), sampled between 1992 and 2001. Previous studies have
shown that lignite burning in the power plant results in the emission of 95% of Hg
contained in the coal. Mercury concentrations were measured in air dried soil samples
using an ALTEC AMA-254 mercury analyzer. The aim of this work is to use natural
soils as geochemical indicators to study the degree of Hg contamination in terrestrial
ecosystems.
The results revealed that surface soil horizons (O, A) have the highest Hg contents, up
to 300 ng g -1 soil, although it was observed a subsurface maximum in Bs horizons (80-
250 ng g -1 ). Mercury enrichment factors, calculated by normalizing to the total Hg
content of the soil parent material, are above 50 in most surface horizons, suggesting a
strong Hg accumulation in the upper part of the soils probably due to the power plant
emissions.
Using a multiple regression analysis, a combination of soil organic matter content
(SOM), pyrophosphate extracted Fe (Fep) and ammonium oxalate Al (Alo) could
explain 88% of the variance of Hg content of these soils. (Hg = 8.2 SOM + 51.1 Fep -
43.8 Alo). Whereas SOM can be regarded as a soil capacity factor to bound Hg, Fep
may indicate a quality factor associated with geochemically active SOM. The negative
load of Alo could be explained through the competition between Al and Hg for SOM
binding sites.
Regarding the temporal trend, Hg contents measured in 1992 were significantly higher
than those measured in the following years. This can be the result of two processes:
losses of soil Hg and a lower Hg deposition due to recent changes in the coal mixture
burnt in the power plant.
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