Crescimento inicial de eucalipto em solo contaminado por Cd, Pb e Zn e tratado com lodo de esgoto e biochar

Abstract

The inadequate disposal of steel slag with high levels of heavy metals, such as lead (Pb) and cadmium (Cd), in the city of Santo Amaro, Bahia, caused the pollution of the environment and the people who live there. Today the city is known to contain the largest Pb contamination in the world. The objective of this work was to evaluate the effects of sewage sludge and its biochar in remediating the levels of Cd, Pb and Zn and the initial development of eucalyptus seedlings in the contaminated soil of the municipality of Santo Amaro. These studies aim to contribute to the determination of remediation methods and suggestion of alternative economic activities for these impacted areas. For this, an experiment was carried out in a greenhouse using a eucalyptus hybrid and application of three treatments to the soil: sewage sludge (40 t ha-1) and biochar (40 t ha-1) and a mixture of 20 t ha-1 of sewage sludge + 20 t ha-1 of biochar, in addition to the negative control (soil without addition of sludge/biochar). After the cultivation period, the available and environmentally available levels of Cd, Pb and Zn in the soil and total levels in the plants were evaluated. The application of biochar promoted better development of eucalyptus seedlings, presenting better results in the production of dry matter of the aerial part, height and diameter. Biochar + sewage sludge considerably reduced (60%) the availability of Zn in the soil, compared to the control. The use of biochar in the soil was efficient in reducing the environmentally available levels of heavy metals, immobilizing them and making them less available to the plant. Eucalyptus seedlings were more efficient in translocating Zn to the shoot in the sewage sludge treatment, showing a better index, while for Cd and Pb the seedlings were more efficient in immobilizing metals in the roots, especially Pb, which showed higher value. The results showed that biochar can be indicated as a remediation agent in the contaminated soil of Santo Amaro, since it promoted a decrease in the mobility and availability of metals in the soil. The sewage sludge can be indicated as a nutritional contribution in the cultivation of seedlings and the eucalyptus seedlings were presented as potential phytoremediation plants of the contaminated soil.