Highly metal-polluted (Pb, Cd, Zn) soil from a non-ferrous mine and smelter site in southern Poland, further referred to as ''Waryn´ski'' soil, was used to test indigenous plant species for stabilization effectiveness of heavy metals in soils. Results of pilot investigations with commercially available cultivars of plant species showed that these cultivars could not grow on this highly polluted soil even with the application of soil amendments to stabilize the heavy metals. Based on these results, mesocosm and field experiments with an indigenous, metal-tolerant ecotype of Deschampsia cespitosa from the Warynski site were carried out. The mesocosm experiment showed that applications of calcium phosphate (3.8% w/w) as a heavy metal-stabilizing amendment decreased Cd and Zn concentrations 2 and 3-fold respectively in leachates, whereas lead content was not significantly changed. This decrease in the concentration of heavy metals in leachates was correlated with a lower accumulation of Pb, Cd and Zn in the roots and shoots of D. cespitosa, ecotype Warynski. In the field experiment, lower accumulations of Cd in roots and shoots and Zn in shoots in the amendment added plot were observed during the second year of investigations. In the first growing season, D. cespitosa plant cover in the amendment enriched mesocosms ranged from 95 to 100%, compared to 10% in mesocosms without calcium phosphate. In the second year of the experiment, in non-amendment enriched mesocosms D. cespitosa was substituted with Cardaminopsis arenosa (95% cover). C. arenosa is an undesirable species for phytostabilization, as it accumulates high amounts of zinc and cadmium in its shoots, even thought it provided better growth cover in not amended soils. However, in amended mesocosms, soil surface cover by D. cespitosa was still very high (90%). Similar results were obtained in field experiments. Addition of calcium phosphate to the soil also resulted in excellent D. cespitosa root system development when compared to soils without amendment. In amended mesocosms, high plant cover and root system development significantly decreased the volume of leachates and improved water retention. These results indicate that the use of D. cespitosa, ecotype Waryn´ski in combination with calcium phosphate as a heavy metals immobilizing agent is sufficient to restore a dense vegetative cover to highly heavy metal-polluted soil.
Phytoremediation, an approach that uses plants to remediate contaminated soil through degradation, stabilization or accumulation, may provide an efficient solution to some mercury contamination problems. This paper presents growth chamber experiments that tested the ability of plant species to stabilize mercury in soil. Several indigenous herbaceous species and Salix viminalis were grown in soil collected from a mercury-contaminated site in southern Poland. The uptake and distribution of mercury by these plants were investigated, and the growth and vitality of the plants through a part of one vegetative cycle were assessed. The highest concentrations of mercury were found at the roots, but translocation to the aerial part also occurred. Most of the plant species tested displayed good growth on mercury contaminated soil and sustained a rich microbial population in the rhizosphere. The microbial populations of root-free soil and rhizosphere soil from all species were also examined. An inverse correlation between the number of sulfur amino acid decomposing bacteria and root mercury content was observed. These results indicate the potential for using some species of plants to treat mercury contaminated soil through stabilization rather than extraction. The present investigation proposes a practical cost-effective temporary solution for phytostabilization of soil with moderate mercury contamination as well as the basis for plant selection.
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