Ácidos húmicos e carvão vegetal ativado na redução da disponibilidade de metais pesados em solo contaminado

Abstract

Lead contamination in Santo Amaro, Bahia, Brazil, originated from the installation of a metallurgical industry in the 60´s. Since its abandonment, atmospheric deposition, and overflow of the tailings reservoir, the highest urban Pb contamination in the world has been observed, leading to serious human health and environmental effects. This study aimed to evaluate the effect of humic acid extracted from vermicompost (AHv), commercial humic acid (AHc) and activated charcoal (CV) carbon sources to reduce the heavy metal toxicity in maize plants. The experiment was carried out in a greenhouse, in pots containing 1 kg of multicontaminated soil, collected in Santo Amaro city, in the 0-20 cm layer, with total Pb, Cd, Ni, Cu and Zn content of 11,707; 50.2; 28.4; 227.7 and 2,154.5 mg kg-1 respectively. The pots were cultivated for 43 days with corn. The doses were based on carbon content (AHV - 50 dag kg-1 AHC - 40 dag kg-1, CV - 55 dag kg-1), corresponding to 0; 0.75; 1.5; 3 and 7.5 g C kg-1 of soil. The metal content available in the soil solution was extracted by Mehlich 1, DTPA pH 7,3 and CaCl2 10 mmol L-1. The soil partial fractionation was performed and the metal fraction in the exchangeable and organic matter fraction was determined. Metal availability in the rhizosphere, and the pH of rhizosphere soil and non-rhizospheric soil, was also evaluated. In the plant, we determined the chlorophyll a and b, yield of shoot and root, and quantification of metals in shoots and roots. In general the application of carbono source study provided a reduction in the available concentration of metals measured by different extractants. In partial fractionation was found increased levels of Pb, Cd and Zn bound to exchangeable fraction of soil, the treatments with HAv and CV, and Ni only in CV. In the organic matter fraction there was an increase of Pb and Ni content according to the increased doses of the carbon. The Pb, Cd, Cu and Ni concentration determined by Mehlich 1 in the rhizospheric soil was higher than the same extraction performed in non-rhizospheric soil for all treatments. The addition of carbon the soil had a strong influence on dry matter production of shoot and root of maize, which were increased according to the increased the doses of organic materials. The content of chlorophyll a and b increased in response to increasing doses of carbon. The highest content of chlorophyll a was due to higher dose of HAv. At the root decreased the content of Pb, Cd and Cu, in the shoot the carbono source caused a reduction in the levels of Cd, Ni and Cu. Results obtained in this work, it was concluded that the AHv and CV can be used in phytostabilization techniques of contaminated sites.