The impact of former mining activity on soils and plants in the vicinity of an old mercury mine (Vallalta, belluno, ne italy)

Abstract

Exploitation of ore minerals (cinnabar, chalcopyrite, sphalerite) from the old mine in Vallalta (Belluno, NE Italy) has resulted in serious environmental impacts, including the acidification of water, and the contamination of soils and plants. Forty-eight soil samples and four wild plants were examined at four sites in the vicinity of the mine (<100 m), where mine waste was discharged. After digestion with aqua regia, chemical analyses were carried out on both soils and plants by inductively coupled plasma-optical emission spectroscopy (ICP-OES) for potentially harmful elements (Cr, Cu, Ni, Pb, Zn, Fe, Mn); the mercury concentration was directly ascertained by atomic absorption spectrometry (AAS). The levels of Ni, Cr, Mn and Zn in the soils were generally below the ‘normal’ levels for uncontaminated sites. Conversely, more than 50% of the examined samples presented Cu and Pb concentrations higher than the phytotoxic level (10 mg kg−1). Iron concentrations exceeded normal values (<300 mg kg−1) in 65% of the examined samples. The mercury concentration was high (6–21 mg kg−1) in all soil samples, mostly above the phytotoxicity limit (10 mg kg−1). Chaerophyllum hirsutum presented the highest Hg levels in roots, up to the phytotoxicity level (10 mg kg−1). Micronutrients Cu, Zn, Fe and Mn showed translocation factors (TFs) of between 0.5 and 1, suggesting that these elements are taken up to a critical concentration and are then arrested in the roots. Iron is less mobile, particularly in C. hirsutum, with the lowest TF of 0.38. The TF for Mn and Hg is >1 in S. nemorum and C. hirsutum; a TF of <0.5 in P. braunii, and particularly in T. officinale, suggests that these metals are most likely to be arrested in their roots. Soil contamination is confined to the proximity (<100 m) of the mine waste. Among the investigated plants, Chaerophyllum seems to be most suitable for phytoremediation of Hg-contaminated sites.