Assessing the control exerted by soil mineralogy in the fixation of potentially harmful elements in the urban soils of Lisbon,Portugal |
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| Authors: | C Costa A P Reis E Ferreira da Silva F Rocha C Patinha A C Dias C Sequeira D Terroso |
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| Institution: | (1) GEOBIOTEC, Geosciences Department, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal |
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| Abstract: | The main purposes of this study are the textural, chemical and mineralogical characterization of the urban soils of Lisbon
and the identification of probable relations between the several soil properties. The results are used to infer which soil
properties control the superficial dispersion of potential harmful elements to human health. Soil sampling was carried out
in 51 selected sites all through the city, under the criterion that such sites should be spaces usually frequented by children.
The concentrations of 42 elements in the >2 mm soil size fraction were determined at a commercial laboratory in Canada (ActLabs,
LTD), by ICP-MS/ICP-OES after an acid digestion with aqua regia. The soil mineralogy was determined by X-ray diffraction in
the <2 and <62 μm size fractions. The results indicate that the urban soils have mainly a sandy texture and a main mineralogical
assemblage of quartz, K-feldspar, plagioclase and calcite. In terms of clay minerals, smectite, illite and kaolinite are the
main clays in the soil. Smectite and illite show a dichotomy in their distribution, with the smectites prevailing in the soils
of the volcanic complex of Lisbon, which are classified as being residual, and illite prevailing in the remaining soils, which
are considered mainly as man-made soils. Smectite seems to exert an important role in the fixation of Ni and Cr. The results
of the geochemical study show that Ni and Cr have concentrations above the soil guideline value established to the UK and
pose a probable risk to human health. |
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