Distribution of Al and Heavy Metals in Bulk Soil and Aggregates at Three Sites Contaminated by the Emissions of a Central Slovak Al Smelter

Large spoils of metal-rich filtercake from the Port Kembla BHP steelworks were characterised by certain physical, chemical and biological parameters. The vegetation was assessed for potential metal hyperaccumulators and the presence of arbuscular mycorrhizae in the rhizospheres. Fresh filtercake (<2 yr old) was charcoal in colour and had a fine (clay loam) texture. Its composition was distinctly different to the older filtercake (3–4 yr) which was similar to the reference soil, being lighter in colour, loamy textured, more aggregated and with higher organic matter. Variability between the two filtercake types also occurred for electrical conductivity and pH. Total trace metal concentrations (Cd, Cu, Pb and Zn) were high and although only minor proportions were in bioavailable forms, the greater percentages in the older filtercake suggested temporal changes in metal speciation. Fresh filtercake was devoid of any plant life and fungal communities. The older material, however, was able to sustain a reasonable environment for plant, bacterial and fungal growth. The vegetation was dominated by Ricinus communis, along with species belonging to the families Asteraceae, Solanaceae, Malvaceae and Apiaceae. Rhizosphere of all these plants harboured mycorrhizae belonging to the Gigaspora and Glomus strains and while trace metal accumulation was observed no plant was a hyperaccumulator. The reference site was principally inhabited by certain Poaceae, Asteraceae and Verbenaceae species. All were mycorrhizal (principally Glomus strains), but no plant was represented on the contaminated site. Here also trace metal accumulation was taking place. The absence of hyperaccumulation in the filtercake was considered a consequence of low levels of bioavailable trace metals. However, as such metal forms may increase over time, particularly for copper and lead, cultivation of known hyperaccumulators could become worthwhile after prolonged exposure (>4 yr). Among the naturally colonising plants, Ricinus communis and Sonchus oleraceus are regarded the most suitable options for zinc and cadmium removal, respectively. Arbuscular mycorrhizal infection (particularly with Glomus and Gigaspora strains) should be promoted for optimum soil reclamation.