The potential of Lolium perenne for revegetation of contaminated soil from a metallurgical site.

A greenhouse study was carried out to determine the possibility of using Lolium perenne for revegetation of soil from a former ferrous metallurgical plant (Naples, South Italy) contaminated by Cu, Pb and Zn at levels above current Italian regulatory limits. Surface soil samples (0-40 cm) from the facility area where raw minerals were disposed (RM1 and RM2), from a nearby unpolluted cultivated soil (C) as control and a 1:3 mixture of the control with the polluted ones (RM1+C and RM2+C) were utilized for the experiment. Revegetation trials were conducted in the greenhouse. At 90 days from seeding, shoot length, chlorophyll content, biomass yield, plant metal uptake and changes of organic carbon content and metal distribution among soil extractable phases defined by sequential extraction were determined. In the mixed substrates (RM1+C and RM2+C) concentrations of Cu, Pb and Zn were still two to three times higher than the Italian regulatory limits. Plants were healthy with 100% survival in all substrates, with no macroscopic symptoms of metal toxicity. The high pH of the soil could be one of the most important parameters responsible for the limited plant availability of the metals. On RM1, RM2 and mixed media, plants experienced retarded growth, reduced shoot length and biomass yield and higher total chlorophyll content compared to those cropped on the control soil, without any evident phytotoxic symptoms. In RM1 and RM2, the plant contents of Cu (19.3 and 12.6 mg kg(-1)), Pb (0.98 and 0.67 mg kg(-1)) and Zn (99 and 88 mg kg(-1)) were higher than that of plants grown on non-contaminated soil (Cu 10.1, Pb < 0.2, Zn 79 mg kg(-1)), but still in the range of physiologically acceptable levels. The distribution of metals in soil was slightly affected by Lolium growth with changes only regarding the organic-bound Cu and Zn pool, with reduction up to 24%. Results indicated that an acceptable healthy vegetative cover can be achieved on the contaminated soil by the proposed revegetation approach and that metals will remain stable over the study period with slight variation of the more available metal forms.