Phytoremedial assessment of flora tolerant to heavy metals in the contaminated soils of an abandoned Pb mine in Central Portugal

Significant accumulation of heavy metals in soils and flora exists around the abandoned Barbadalhos Pb mine in Central Portugal. Soil and plant samples [49 species] were collected from two line transects, LT 1 and LT 2, in the mineralized and non-mineralized area, respectively to gain a comprehensive picture of heavy metals in soils and flora to assess its potential for phytoremediation. Phytosociological inventories of the vegetation were made using the Braun-Blanquet cover-abundance scale. Metal concentrations in soil ranged from (in mg kg−1): 98–9330 [Pb], 110–517 [Zn], 7.1–50 [Co], 69–123 [Cr], 31–193 [Cu], 33 400–98 500 [Fe], 7.7–51 [Ni], 0.95–13 [Ag], 2.8–208 [As], and 71–2220 [Mn] along LT 1; and 24–93 [Pb], 30–162 [Zn], 3.7–34 [Co], 61–196 [Cr], 21–46 [Cu], 24 100–59 400 [Fe], 17–87 [Ni], 0.71–1.9 [Ag], 4.3–12 [As], and 44–1800 [Mn] along LT 2. Plant metal content ranged from (in mg kg−1): 1.11–548 [Pb], 7.06–1020 [Zn], 0.08–2.09 [Co], 0.09–2.03 [Cr], 2.63–38.5 [Cu], 10.4–4450 [Fe], 0.38–8.9 [Ni], and 0.03–1.9 [Ag] along LT 1; and 0.94–11.58 [Pb], 2.83–96.5 [Zn], 0.12–1.44 [Co], 0.21–1.49 [Cr], 1.61–22.7 [Cu], 4.6–2050 [Fe], 0.51–4.81 [Ni], and 0.02–0.31 [Ag] along LT 2. Plants with highest uptake of metals were: Cistus salvifolius (548 mg Pb kg−1), Digitalis purpurea (1017 mg Zn kg−1 and 4450 mg Fe kg−1). Mentha suavolens and Ruscus ulmifolius were seen to hyperaccumulate Ag (1.9 and 1 mg Ag kg−1, respectively). More metals and higher concentrations were traced in plants from LT 1, especially for Pb and Zn.

► Metal content of Pb mine soils quantified and assessed by contamination indices.
► Pb mine flora evaluated as plants tolerating high contamination and poor soils are vital for phytoremediation.
► Phytosociological studies combined with metal analysis of plants for a complete picture.