Keywords: environmental pollution, sewage sludge, heavy metals, chemical changes, Oxisol, maize grains, Zea mays L, agriculture, soil changes, tropical areas, soil contamination, Brazil, fertilizers, zinc, copper, nickel, cadmium, lead, chromium
Chemical changes in an Oxisol cultivated with maize (Zea mays, L.) after six years disposal of sewage sludge
Sewage sludge is composed of predominantly organic matter and can be used to improve soil characteristics, such as fertility. Therefore, its application in agriculture is an adequate alternative for its final disposal. However, there is a lack of information on its long–term effects on soil changes in tropical areas. Thus, the objectives of this study were to determine: (a) the effect of sewage sludge application on heavy metal build–up in soil and maize grains and (b) the effects of soil amendment with sewage sludge on the chemical properties of a Brazilian Oxisol. Besides the increasing levels of Zn, Cu, Ni, Cd, Pb and Cr, amending soil with sewage sludge also alters the distribution of these metals by increasing the mobile phases, which correlated significantly with the increase in metal extraction with two single extractants, Mehlich 1 (HCl 0.05 mol L−1 + H2SO4 0.0125 mol L−1) and DTPA (Diethylenetriaminepentaacetic acid). Nevertheless, metal build–up in soil and plants was within the allowed limits. The data obtained does not indicate any expressive drawbacks in the use of sewage sludge as a soil amendment, as the heavy metal concentrations observed are unlikely to cause any environmental or health problems, even overestimated loadings.