Bentonite application in the remediation of copper contaminated soil

The concern on heavy metals from commercial fertilizers for fertilization of crops when they are intended for human consumption has increased specifically, horticultures and grains. Several procedures have been proposed to reduce the concentration of heavy metals in the soil; among these are, the application of materials that are able to adsorb these elements, making them less available to plants. This study aimed to evaluate the bentonite for remediation of artificially copper contaminated soils, grown with beets, radish and corn. The experiment was conducted in a greenhouse in a completely randomized design, with four replicates. A loamy sand soil planted with radish and corn was contaminated with 100 mg kg-1of copper, while for beets, the soil was contaminated with 250 mg kg-1 of copper as copper sulphate (Cu2SO4). Bentonite treatments consisted of four doses of bentonite: 0, 30, 60 and 90 t ha-1. The copper content in the soil and in plants, as well as the translocation index in the plants was evaluated. The results were analyzed by the F test and polynomial regression was used for adjustment of significant data. Bentonite decreased the copper content in the dry phytomass of the plants, affected significantly the copper accumulated in the roots of beets and radish, and in the aerial part of radish. The copper translocation index in beets reduced with bentonite doses, and consequently the quantity of copper on beets was higher than those levels permitted for human consumption. Application of bentonite in contaminated soils grown with radish and corn improved their amelioration; on the other hand, the soil grown with beets did not present any amelioration.   Key words: Heavy metal, accumulation, vegetables.