The use of indigenous plant species and calcium phosphate for the stabilization of highly metal-polluted sites in southern Poland

Highly metal-polluted (Pb, Cd, Zn) soil from a non-ferrous mine and smelter site in southern Poland, further referred to as Warynski 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 Warynski 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.