Potencial de resíduos orgânicos na atenuação de contaminação por cobre de solo e água
Cipoleta, Nathalia Sprovieri
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The aggravation of environmental problems has stimulated discussion about new ways of producing in the field. The term alternative agriculture covers non-conventional agricultural systems, such as natural, ecological, biodynamic, permaculture, biological, organic and agroecological systems. In addition to organic inputs for fertilization and soil conditioners, crops grown in alternative systems also require natural products to combat pests and plant diseases. Heavy metals such as arsenic, cobalt, copper, lead, and zinc, which occur as impurities in these products, can reach undesirable levels and cause contamination of soil, water, and sediments. The Bordeaux mixture is a fungicide composed of hydrated copper sulphate (CuSO4.5H2O) and quicklime (CaO) and is legalized for use in alternative agricultural systems, but may increase copper (Cu) contents in the soil and affect soil and water quality. The objective of this work was to evaluate the soil and water contamination potential of copper contained in the Bordeaux mixture; ii) to evaluate the retention of Cu in clay soil fertilized with waste and organic conditioners; and iii) estimate the potential for soil and water contamination. Copper contamination potential was evaluated based on a literature review focused on articles, dissertations and theses published, focusing on alternative agricultural production systems. The retention of Cu and its soil and water contamination potential were evaluated by means of a laboratory test using clay tubes filled with clay soil treated with three types of organic materials (Bokashi, coconut fiber, and leonardite) in three doses of Bordeaux mixture. The test lasted 47 days and regular percolate samplings were performed. At the end of the experiment, the content of Cu retained in the soil was determined. Residues and organic conditioners, in all tested doses, retained more than 55% of the applied Cu, even after extraction with strong acid. Bokashi presented the lowest concentration of Cu in the percolate (0.621 mg L-1) and the lowest concentrations retained in the soil, after extraction with weak acid (68.4% in the lowest dose) and with strong acid (59.9% in the highest dose ). Leonardite showed the highest concentration of Cu in the percolate (1.4% in the highest dose) and the highest concentrations retained in the soil, after extraction with weak acid (98.2% in the medium dose) and with strong acid (94.1% in the lowest dose). It is concluded that leonardite, a material rich in humic substances, has high Cu adsorption capacity and may be useful in organic production systems to mitigate contamination of soils and water with Cu.