Heavy metal accumulation and tolerance in plants from mine tailings of the semiarid Cartagena–La Unión mining district (SE Spain)

Mine tailings are a characteristic of landscapes where mineral extraction has occurred. These tailings usually contain high heavy metal concentrations and have low fertility. In arid and semiarid zones, erosion may be an additional problem. The removal of these tailings is often impractical due to their large volumes. Therefore, a need exists to develop in situ low cost technologies to effect surface stabilization. The use of vegetation can be an attractive option, since there are some native plant species that can colonize parts of these polluted sites unaided. Some edaphic factors were investigated, including heavy metal concentrations, in three mine tailings from a semiarid mining zone in Southeast Spain. High total metal concentrations were found: 5000–8000 mg/kg for lead and 7600–12300 mg/kg for zinc. Two of these mine tailings had pH values between 6 and 7, while the other was acidic, with a pH of 2.5. Metal solubility was pH dependent, with more than 10% of the total zinc soluble in the acid substrate and less than 1% in the neutral substrates. The metal concentrations (copper, lead and zinc) in shoots of native vegetation colonizing in these sites were studied. No species of hyperaccumulators were found. The highest concentrations were found in Zygophyllum fabago, with 530 mg/kg zinc, Helichrysum decumbens with 390 mg/kg lead, and Tamarix sp. with 11 mg/kg copper. An analysis of the rhizospheric soil of these plants indicated that Lygeum spartum grew in pH 3 soil and had low metal concentration in shoots (40 mg/kg zinc and 41 mg/kg lead).