Fjölrit RALA - 15.06.2004, Síða 131

Mercury enrichment factors (HgFE), which were calculated by normalizing to total A1
content in the deepest mineral horizon, showed values above 10 in upper horizons of the
profiles N-2, N-3 and N-4 (Italy), N-5 (Azores Islands), N-7 (Iceland), N10 (Canary Islands),
N-14 (Greece) and N-15 (France). It is in the latest soil where HgFE reach the highest value,
30. On the other hand, HgFE lower than 5 were found in soils from Hungary (N-17, N18 and
N-19), Canary Islands (N-12), Greece (N-13 and N-14a), Iceland (N-9) and France (N-16).
The mean value of HgFE for upper horizons of all the studied profiles is 7.4 ±6.8 and the
vertical profile of HgFE is quite similar to the vertical distribution of total Hg content,
according with the strong Hg accumulation that was observed.
The maximum concentrations of total Hg found in upper horizons can be related to a
higher degree of soil evolution. It means that, during long periods without significant volcanic
activity, the pedogenetic processes can lead the soil towards an increase of soil organic matter
content as a consequence of the establishment and development of vegetation. This idea was
exposed by Tomiyasu et al. (2003) to explain the similarities between total Hg and soil
organic matter distribution in volcanic soil from Japan. In addition, other properties of soils
developed from volcanic materials, as the presence of components like Al(Fe)-humus
complexes, allophane and/or imogolite, can also promote Hg accumulation. However in
periods with important volcanic activity, new erupted inorganic material (sand, pumice,
volcanic ash, etc.) could be deposited over the old soil given a new pedogenetic cycle. In
these new conditions, the lower degree of soil evolution may explain the lower total Hg
values observed in some of the studied soils.
For all soil significant correlations (p<0.01) between total Hg content and several A1 and Fe
extractions were found (0.62 for A1 extracted with CuC^; 0.50 and 0.47 for A1 and Fe
extracted with Na-pyrophosphate; 0.42 and 0.34 for A1 and Fe extracted using ammonium-
oxalate, and 0.49 and 0.46 for A1 and Fe extracted with NaOH and Na-dithionite
respectively). Correlation coefficients showed a small increase when andic horizons (as
defined by García-Rodeja et al, 2004) were considered separately. Stepwise regression
analysis was performed to identify the most significant properties of andic horizons related to
total Hg content. The model obtained, which includes reactive A1 and Fe forms, explains 90%
of the variance. The results of this statistical approach suggests that, in addition to soil organic
matter, the presence of amorphous (organic and/or inorganic) A1 and Fe components may be
important for Hg accumulation in volcanic soils.
References
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Tomiyasu, T., M. Okada, R. Imura, and H. Sakamoto. 2003. Vertical variations in the
concentratoion of mercury in soils around Sakarajima Volcano, Southem Kyushu, Japan.
The Sci. Tot. Environm. 304:221-230.
Coffey, M.T. 1996. Observations of the impactt of volcanic activity on stratospheric
chemistry. J. Geophys. Res. 101:6767-6780.
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mercury from naturally enriched substrate. Atmos. Environm. 36:3241-3254.
García-Rodeja, E., J.C. Nóvoa, X. Pontevedra, A. Martínez-Cortizas, and P. Buurman. 2004.
Catena 56:155-183.
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