IMPACT OF SUBSTRATE ACIDIFICATION ON THE PLANT AVAILABILITY OF SOME TRACE ELEMENTS IN A COAL WASTE MATERIAL

Abstract

Coal waste dumps present potential sources of toxic elements, which may enter surrounding soils, water bodies, and can be transferred into plants. Acidification of the dump material as a consequence of sulphide mineral oxidation can foster element mobilization and plant uptake. In the present study we explored the elemental composition (Co, As, Cu, Pb, Mn, Zn and Cr) of substrate from the waste heap of the coal mine "Heroiv Kosmosy", Ukraine and investigated effects of substrate acidification on leaching and plant accumulation of the elements, considering two native grass species wall barley (Hordeum murinum) and japanese brome (Bromus japonicus). Both species were cultivated in a greenhouse experiment on substrate from the waste dump. The plants were watered with acidic treatment solutions at a pH range from pH 2–7. Element concentrations in leachate solutions, plant biomass and aqua regia extracts of the substrate were analyzed by ICP-MS. The pH of the substrate collected from the coal dump was 7.68 ± 0.02 the value and the electrical conductivity was 1200 ± 25 μS/cm. The substrate contained low concentrations of plant available (mineral) N (0.09 ± 0.01 mg/kg), and low concentrations of DL-extractable phosphate (0.016 ± 0.01 mg/kg). The aqua regia extractable concentrations of the investigated elements exceed the maximum allowable concentration in 59; 38; 47; 11.5; 2.5; 25 and 64 times, respectively. Decreasing the pH in the substrate significantly increases the concentrations of all studied elements in leachate solutions. The growth experiment showed that both H. murinum and B. japonicus, respectively germinated and grew on the substrate. After 21 days of plant growth H. murinum developed 7 ± 2 cm roots, and average shoot size was 20 ± 1 cm. In contrast, B. japonicus showed a root length 4 ± 0.5 cm and shoots were 8 ± 0.5 cm (pH=2). Decreasing the pH-values in the substrate led to increased element abortion in both plant species. However, H. murinum preferably accumulated the investigated elements in the roots while B. japanicus showed a substantially higher root–shoot transfer. The calculated translocation factors ranged between TF = 0.4–6.6 (B. japanicus) and between TF = 0.1–1.7 in H. murinum. We could demonstrate that substrate acidification strongly impacts plant availability in coal waste material. Both plant species are meaningful candidates for a phytoremediation of soil waste heaps in the Western Donbas.