HEAVY METALS IN SOILS OF A LEAD MINING AND METALLURGY AREA. II - FORMS AND PLANT AVAILABILITY

The forms and availability of heavy metals in contaminated soils determine the uptake potential of plants and water contamination by leaching. In this study different methods of chemical extraction were used, in order to identify the forms of Pb, Cd, Cr, Ni, Cu, and Zn and evaluate the availability of these pollutants for sunflower (Helianthus annuus L.), black oat (Avena strigosa Schreber) (exotic species) and Bahiagrass (Paspalum notatum Flugge) (native Species), as indicators, in soils of Pb mining and metallurgy in Adrianopolis, state of Parana, Brazil. Soil samples were collected in the 0-40 cm layer in four environments of the area: soil 1 - control (native forest); soil 2 - waste in soil profile,- soil 3 - near the factory chimney (deposition of particulate material); soil 4 - heavy deposition of waste. The following extraction methods were used: DTPA-TEA pH 7.3; Ca(NO3)(2) 0.5 mol L-1; HNO3 0.5, 1.0 and 4.0 mol L-1, and concentrated HNO3/HCl (3:1). The plants were grown in a greenhouse, with three replications. The increase of pseudo-total, exchangeable and non-exchangeable heavy metal contents was verified; the highest contents of Pb and Zn Were extracted by HNO3/HCl; 9,678.2 and 894.8 mg kg(-1), respectively. Soil heavy metals based on acid extractors HNO3 0.5, 1.0 and 4.0 mol L-1 and HNO3/HCl were strongly correlated with each other. The extractor based on chelation (DTPA-TEA pH 7.3) was not efficient to predict the availability of heavy metals for plants under the study conditions. The nitric extractions should be preferred to determine Pb and Zn plant availability in the area.