DISTRIBUCIÓN DE ELEMENTOS METÁLICOS (Cr, Mn, Ni, Cu, Zn, Pb, Th) Y ARSÉNICO EN DOS SUELOS POLICÍCLICOS PODSÓLICOS

R. PIÑEIRO REBOLO, E. PEITEADO VARELA Y A. MARTÍNEZ CORTIZAS

Departamento de Edafología y Química Agrícola, Universidad de Santiago de Compostela, Campus Sur s/n, 15782 Santiago de Compostela

Abstract

The fine earth (FE, <2mm) and silt+clay (SC, <50 µm) fractions of two polycyclic podzolic soils, Pena Cebral (PC) and Curro Vello II (CVII), from northwestern Spain were analyzed for some metalic elements (Cr, Mn, Ni, Zn, Pb, Th) and As. The vertical distribution was studied using detailed concentration profiles, concentration ratios between fractions and enrichment factors. The concentrations obtained for the fine earth of Pena Cebral are: Cr below or close to the detection limit (DL, <50 mg kg-1); Mn <30-373 mg kg-1; Ni <3-27 mg kg-1; Cu 3-14 mg kg-1; Zn 22-52 mg kg-1; As <5-13 mg kg-1; Pb 19-75 mg kg-1; and Th 10-23 mg kg-1. For Curro Vello II are: Cr below DL in all fine earth samples; Mn 40-285 mg kg-1; Ni <5-15 mg kg-1; Cu <3-12 mg kg-1; Zn 15-88 mg kg-1; As <5-11 mg kg-1; Pb 24-56 mg kg-1; and Th 10-32 mg kg-1. All the elements showed higher concentrations in the SC than in the FE and also than those estimated for the sands (up to 4.5 times). Moreover, those elements with concentrations below DLs showed detectable contents in the fine fractions. The distribution of the elements was found to be affected by podzolisation (Zn, As and Pb) and deposition of atmospheric pollutants (Mn, Zn, Cu and Pb). The chronology of Zn, Cu and Pb enrichments in both soils suggests a direct influence of atmospheric pollution by mining and metallurgy since ancient times, which is consistent with the findings of other studies using ice cores, lake sediments and peat bogs in Europe and particularly in NW Spain, stating the importance of human activities in the cycles of these elements. On the other hand, the higher enrichment found in the Curro Vello II soil for elements which are tracers of the emissions of a nearby coal-fired power station and vehicles, shows the incidence of recent point sources of atmospheric pollution in the area where this soil is located. The Th profile seems to be independent of podzolisation, but it probably is related to the leaching of the element due to disolution of the host minerals under an extremely acid environment with high sulphate availability.

Key words: polycyclic soils, podzolisation, metallic elements, arsenic, atmospheric pollution.