Cadmium fractions in an acid sandy soil and Cd in soil solution as affected by plant growth

Abstract

In a previous experiment, plants were able to immobilize or solubilize Cadmium (Cd) in a sandy acid soil enriched with 40 μmol Cd kg–1, because Cd solution concentration was decreased by maize (Zea mays) and sunflower (Helianthus annuus), and increased by flax (Linum usitatissimum L. ssp. usitatissimum) and spinach (Spinacia oleracea). It is assumed that the equilibrium with Cd fractions in the soil solid phase and the chemical form of Cd in the soil solution were affected. In the present study, the effect of the four plant species mentioned above on Cd binding in soil was investigated by means of a fractionation of soil Cd with a sequential extraction of seven steps. The seven fractions of Cd are operationally defined by the extraction sequence that follows the order of increasing acidity with extractants of different complexing and redox properties. In the unplanted soil, Cd was predominantly present in the exchangeable Fraction I (F. I) and easily mobilizable Fraction II (F. II) (64%). Significant concentrations of Cd were found in F. III (occluded in Mn oxides; 22%) and F. IV (organically bound; 10%). Fractions V (occluded in poorly crystalline Fe oxides), F. VI (occluded in well crystallized Fe oxides), and F. VII (residual fraction) amounted to less than 5% of the total soil Cd concentration. The plants changed the binding of Cd in soil in a different manner. All plants decreased F. I, but F. II was increased by maize and spinach, decreased by flax or remained unaffected by sunflower. Fraction III was not affected by maize and flax, but decreased by sunflower and spinach, and F. IV was not affected by sunflower and spinach, but was increased by maize and flax. These changes of Cd fractions were not related to the changes the plants had caused in total Cd or Cd2+ concentration of the soil solution. These results show that plant species differ in how they affect Cd binding to the soil solid phase, but this effect is not related to how they affect Cd in soil solution. The mechanisms by which plants affect the relationship between the soil solid and liquid phase are still unclear.

Application of white mustard and oats in the phytostabilisation of soil contaminated with cadmium with the addition of cellulose and urea

“…The findings of this study confirm it. According to literature reports (Bolan et al 2014;Stritsis et al 2014;Li et al 2016), the level of cadmium in a soil solution depends on the balance between processes of mobilisation and the immobilisation of metals. These processes are controlled by the physicochemical properties of soil (such as pH, exchangeable cation capacity), activity and diversity of soil microorganisms, and the growth and development of plants.…”

Calorific Value of Festuca rubra Biomass in the Phytostabilization of Soil Contaminated with Nickel, Cobalt and Cadmium Which Disrupt the Microbiological and Biochemical Properties of Soil

“…For this reason, heavy metal concentrations in the bioavailable fraction can differ in soils with similar pollution levels. Numerous research studies have demonstrated that microorganisms play an important role in phytoremediation by secreting specific metabolites, siderophores and ligands [31][32][33].…”

Mobilization of cadmium from festuca ovina roots and its distribution between operational fractions in soil

“…Hence, measurements of total metal concentrations are not enough to specify their mobility, bioavailability and toxicity (Conesa et al 2010, Bolan et al 2014. Based on ways of their binding by soil constituents and the strength of the created bounds, seven geochemical fractions of metals can be described: (1) a mobile fraction containing soluble and non-specifically sorbed metals, as well as metal-organic complexes, (2) an easily mobilizable fraction including metals specifically sorbed on the particle surface and bound to carbonates, (3) occluded in manganese oxides, (4) bound to soil organic matter, (5) occluded in amorphous iron oxides, (6) occluded in crystalline iron oxides, and (7) structurally bound in soil minerals (Conesa et al 2010, Stritsis et al 2014). Chemical speciation of metals determined in soil changes over time, and their redistribution between operational fractions is possible (Majewska and Kurek 2007, Kabata-Pendias 2011, Oves et al 2012).…”

“…This is influenced by the physico-chemical properties of the soil (e.g. pH, cation exchange capacity, particle size, content and type of soil organic matter), activity and diversity of soil microorganisms, and growth of plants (Stritsis et al 2014, Li et al 2016.…”