Mobility of trace elements in arable soils from the Bobov dol valley, Bulgaria
Ivona Nikova, VeneraTsolova
Abstract: Soils in the Bobovdol valley are influenced by a complex anthropogenic impact that increases the geochemical and pedo-morphological diversity in the region. In order to assess the mobility of some essential trace elements and toxicants three soil types used for agriculture were studied. They are located at a different distance from the coal fired Bobovdol Thermoelectric Power Plant (Bulgaria) and thence diversely enriched with Cu, Zn, Pb and Mn. The local geochemical particularities, profile distribution of elements and key soil features are used to assess the mobility of Cu, Zn, Pb and Mn.
According to the results obtained studied soils are characterized by low total and mobile content of Pb, Cu, Zn, and Mn. Their total contents are lower than the background values in bulgarian soils but lithic discontinuity or fly ash admixtures entail higher amounts. All elements are mainly concentrated in the silt fractions but river sediments (in Gleyic Fluvisol – profile 7) are richer in clays and clay-metal complexes. Organo-metal complexes of the elements are more typical of the strongly altered anthropogenic horizons in Pretic-Carbic Luvisol (profile 6).
Despite of all various geochemical and physicochemical conditions in soils, studied elements form stable associations with soil components which determine their slight mobility and strong competition.
There is a well-pronounced antagonism among the mobile forms (water-soluble and ion-exchangeable) of Cu, Zn, Mn and Pb and the most competitive ions are: Cu-Pb and Zn-Mn in reducing environment of river`s sediments while in the case of preferential adsorption of lead onto the mineral colloids: Zn-Pb and Mn-Pb. Copper is the least mobile element in the studied soils regardless of soil type and features while the bioavailability of lead is the most dependent on the soil type.
The content of mobile forms of the elements in studied soil types is non-toxic and decreases in the following order of average concentrations: Mn (0.72 mg/kg) > Pb (0.55 mg/kg) > Zn (0.09 mg/kg) > Cu (0.05 mg/kg).
According to the results obtained studied soils are characterized by low total and mobile content of Pb, Cu, Zn, and Mn. Their total contents are lower than the background values in bulgarian soils but lithic discontinuity or fly ash admixtures entail higher amounts. All elements are mainly concentrated in the silt fractions but river sediments (in Gleyic Fluvisol – profile 7) are richer in clays and clay-metal complexes. Organo-metal complexes of the elements are more typical of the strongly altered anthropogenic horizons in Pretic-Carbic Luvisol (profile 6).
Despite of all various geochemical and physicochemical conditions in soils, studied elements form stable associations with soil components which determine their slight mobility and strong competition.
There is a well-pronounced antagonism among the mobile forms (water-soluble and ion-exchangeable) of Cu, Zn, Mn and Pb and the most competitive ions are: Cu-Pb and Zn-Mn in reducing environment of river`s sediments while in the case of preferential adsorption of lead onto the mineral colloids: Zn-Pb and Mn-Pb. Copper is the least mobile element in the studied soils regardless of soil type and features while the bioavailability of lead is the most dependent on the soil type.
The content of mobile forms of the elements in studied soil types is non-toxic and decreases in the following order of average concentrations: Mn (0.72 mg/kg) > Pb (0.55 mg/kg) > Zn (0.09 mg/kg) > Cu (0.05 mg/kg).
Keywords: agricultural soils; antagonism; physicochemical conditions; trace elements
Date published: 2017-11-03
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