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Gossan wastes represent one of the most hazardous mine wastes in several mining areas from the Iberian Pyrite Belt. Phytostabilisation of mine wastes with Cistus ladanifer L. could be a good option, but its growth and germination are impaired by substrata conditions. To overcome these limitations, application of organic and inorganic amendments may speed up the growth of C. ladanifer while improving the mine wastes. This study evaluated the simultaneous influence of different application rates of amendments and growth of C. ladanifer on chemical and biological properties of gossan wastes. Amendments used were mixtures (30, 75, 150 Mg/ha, 1:1:1) of rockwool, agriculture wastes and wastes from liquor distillation of Arbutus unedo L. fruits. A microcosm assay with four treatments was carried out (control and three amended treatments) under controlled conditions in a greenhouse during 505 days. Cistus ladanifer was sown in half of the pots from each treatment while the remainder was left bare. Gossan wastes had large total concentrations of several elements (g/kg; Al: 24.8, As: 3.03, Cu: 0.23, Pb; 9.21) whereas the available concentrations of these elements were small (< 5.7 % of total). The amendments applied (in particular at 75 and 150 Mg/ha) improved the structure and increased the water-holding capacity, pH and nutrient concentrations in the available fraction of the gossan materials. They also led to increases in dehydrogenase and β-glucosidase activities and in plant growth (plant cover, plant height, length of young leaves, fresh biomass). In addition, plants from amended treatments presented lower concentrations of hazardous elements in shoots than plants from unamended control. The presence of the plant did not increase the available concentrations of hazardous elements in wastes, except for As when 150 Mg/ha of amendments was applied. Phytostabilisation with C. ladanifer using a Technosol, resulting from the application of the studied amendments at 75 and 150 Mg/ha to gossan materials, seems a promising solution for rehabilitation of this type of mine wastes. [ABSTRACT FROM AUTHOR]

Abstract: The rhizosphere is a narrow zone of soil influenced by plant root and their exudates and its extent varies with soil type, plant species, age and many other factors. The rhizosphere microenvironment therefore has different characteristics from those of bulk soils. In the present study, the physicochemical parameters, exchangeable micronutrients (extracted with 1M NH4Cl), available micronutrients (extracted with Mehlich-III: Fe, Mn, Cu, and Zn), toxic metals (Cr, Pb, Ni, Cd), the Fe associated with the organic matter (extracted with Na-pyrophosphate) and the poorly crystalline Fe (extracted with 0.2M oxalic acid) were studied in the bulk soil and in the rhizosphere of the spontaneous vegetation growing at an abandoned copper mine. The natural vegetation colonising the mine dump included two species of Ericaceae (Erica cinerea, Calluna vulgaris) and Salix atrocinerea, whereas only the first two grew on the mine slope. The results showed that plants influence the physicochemical conditions of the rhizosphere, although not all in the same way. Thus the pH of the rhizosphere of the ericaceous species was extremely low, approximately 2–3units lower than the pH of the bulk soil, whereas the pH of the Salix rhizosphere remained close to the respective bulk soil, which has a pH of 6.6. Furthermore, the concentration of organic matter was higher in the rhizosphere than in the bulk soil. In general the same pattern was observed for the most labile fractions of the micronutrients and toxic metals, with higher concentrations in the rhizosphere than in the bulk soil. However, there were clear differences between the ericaceous species and Salix, which prevents general conclusions being reached about the processes to which trace metals are submitted in the rhizosphere. On the other hand, although the elements under study are included in the term trace metals, they display different geochemical behaviour. Thus the exchangeable fraction was clearly correlated with the TOC for all micronutrients except Cu, presumably because the organic matter selectively adsorbs this element, thereby reducing its mobility. Finally, as regards the potential toxicity, only the concentrations of Cu and Fe surpassed the limits above which phytotoxicity may occur, while toxic metals were present at very low concentrations. [Copyright &y& Elsevier]