A BIOGECHEMICAL APPROACH FOR THE ENVIRONMENTAL CHARACTERISATION OF MINE LANDS

Abstract The determination of PTE environmental impacts at mine lands is a complex issues, since it regards different environmental matrix, as earth material (soils and waste-rocks), superficial and underground waters and also living beings. All of these can be investigated by biogeochemical tools, as they are very useful to understand how PTE move from waste-rocks to the surrounding ecosystems and how a careful mine land management can control their impacts. This project was carried out in order to check and develop analytical methodologies for the evaluation of: 1. PTE contamination of earth materials (soil or waste rock), with a special care for arsenic, one of the most dangerous elements for human health; 2. AMD evaluation, by the application of different analytical methodologies (static and kinetic tests); 3. biogeochemical features of wild flora growing on mine sites, in order to collect useful information for mine lands remediation. AMD evaluation was done by the applications of AMIRA procedure (IWRI & EGI, 2002), that allowed to identify the acid production or neutralising potential of earth materials. Moreover, an important tool for geochemical assessment of abandoned mine-waste dumps was applied, as it is a quick, cost-effective and qualitative leach procedure, designed by the Environmental Protection Agency (1994) to evaluate the impact of contaminated earth material on groundwaters. This kinetic test provides an insight into the behaviour of the waste-rocks during the interaction with meteoric water and gives useful indication of the potential chemical composition of the run-off from the weathered surface of mining areas. Moreover, the relationship between earth materials and plants growing on mine areas were investigated and metal tolerance strategies were identify by the calculation of the appropriate biogeochemical parameters as Bioaccumulation Factor and Traslocation Factor. These approaches have been developed on two ancient mine sites, with different geo-environmental setting: Rosia Montana mining area (Romania) and Gromo-Gandellino mining area (Valseriana, Northern Italy). Rosia Montana mining area (Romania) is a hydrothermal gold deposit hosted in andesites and dacites of Neogene age, piercing the pre-volcanic sedimentary basement as breccia pipes, that host polymetallic sulphides and Au-Ag-Te mineralisations. Century of exploitation caused a significant environmental damage and the excavation and exploitation of tunnels and open pits has generated a large amount of waste-rocks dumps, some of them located close to villages. Private company provided remediation plans for the past mining activity and mitigation plans for reopening. Gromo-Gandellino ancient mining area is a Ag – Fe ore deposit made up mainly by sulphide, sulphosalts and carbonate, intensely exploited in the medieval epoch and abandoned in the early decades of 20th century. The area is not exploited at the present time, but the numerous underground cavities and waste-rock dumps, some of them located very closed to villages, testify the historical activities linked to the exploitation of Fe, Zn, Pb, Ag and Cu mineralisations. At Hop waste-rock dump (Rosia Montana mine site, Romania) the spatial heterogeneity is well represented. Earth material is composed by two different rock types: (1) the so-called WR1 samples, a source of acid drainage ; and (2) the WR2 samples, able to buffer the production of acidic water. On the whole, Hop waste rock dump is however a source of acid drainage, as showed both by static and kinetic tests. These last have confirmed to be an important tools for geochemical assessment of abandoned mine-waste dumps, as they are a quick, cost-effective and qualitative leach procedure to evaluate the impact of contaminated earth material on groundwater and to assess metal mobilisation from waste-rocks. The tree species growing on Hop waste-rock dump, belonging to Salix spp., B. pendula and P. tremula, are able to tolerate limiting conditions (such as acid pH values and mean As content of 80 mg/kg), as known from the literature. They actively accumulate Cu and Zn in their tissues, specially in leaves, although they can not be considered as hyper-accumulators. On the other hand, the same species act as excluders for As, whose concentration in plant tissues are lower than in soils, exceeding however toxic values.Salix spp. represents the species more able to tolerate different environmental situations and to grow on strong acid substrates, acting as a pioneer species that could be used for revegetation of mine lands and stabilization of dump slopes, even on the area still not vegetated. At Gromo-Gandellino mine site, the occurrence of waste-rock dumps represents an environmental hazard for the area: soil heavy metal concentrations is about one order of magnitude higher than in natural soils, specially at Coren del Cucì site, located in the vicinity of Gromo village. The mining area is colonised by the metal tolerant species C. vulgaris and D. filix-mas. These plants behave as excluders and accumulation occurs only in roots, where internal metal detoxification mechanisms might exist in addition to exclusion strategies. So, they can be used surely as slope dump “stabilizators” and, in particular, C. vulgaris appears interesting for mine land restoration and soil stabilization of Cu, Zn, Pb, Ni, Cd and As. The biogeochemical characterisation of these mine lands gave useful information to support their management, as it provided information for the choice of sites that need priority remediation activities, and identified, within these sites, the areas responsible for contamination. Moreover, the identification of metal tolerance species and their strategies provided useful information for project of rehabilitation, but also highlighted how PTE move through food webs.