Fábio Cesar da Silva

Efeito do período de incubação e de doses de composto de lixo urbano na disponibilidade de metais pesados em diferentes solos

-1 de composto de lixo, em periodos de 0, 16, 32, 64 e 150 dias. A maioria dos metais pesados teve sua disponibilidade reduzida nos primeiros periodos de incubacao, sendo esse efeito dependente de textura, pH e teor de materia orgânica do solo. O uso continuado de composto de lixo, principalmente nas doses mais elevadas, pode resultar em riscos de contaminacao do ambiente pelo efeito cumulativo, em especial nos solos Latossolo Vermelho-Amarelo distrofico, Chernossolo Haplico ortico e Nitossolo Vermelho eutroferrico, cujo periodo para reducao da disponibilidade dos metais pesados varia de 6 a 12 meses. Termos para indexacao: residuo solido, propriedade fisico-quimica, utilizacao de residuos, toxicidade do solo. Effect of incubation period and doses of urban trash compost on the readiness of heavy metal in different soils

Evaluation of chemical extractants to assess metals phytoavailability in Brazilian municipal solid waste composts

Municipal solid wastes (MSW) can be composted to become an organic fertilizer. However, besides plant nutrients, it can also contain high concentration of some toxic metals than can pollute agricultural soils, contaminate food, animals and human being. A greenhouse experiment was carried out for two purposes: i) to evaluate the concentrations of cadmium, copper, chromium, nickel, lead and zinc in four Brazilian MSW composts, and, ii) to know which is the best solution for extracting those metals in phytoavailable form from the composts. In order to evaluate the phytoavailability of metals, they were extracted with six chemical extractants: i) water, ii) 0.05 mol L-1 Ca(NO3)2, iii) 0.1 mol L-1 HCl, iv) 0.005 mol L-1 DTPA at pH 7.3, v) 0.05 mol L-1 CaCl2 and vi) Mehlich 3 solution. In addition, lettuces were cultivated as a test plant in pots containing 1.8 kg of MSW compost as substrate. Fifty-six days later, lettuce plants were harvested. New lettuces were then planted for a second cycle, and then harvested after fifty-six days. Semi-total concentration of metals in composts and total in plants was also determined through an extraction with nitric-perchloric acid. Semi-total concentration of Cd and Pb exceeded the intervention limits from Brazil in the four studied composts, and lettuce plants were polluted by those two elements. Therefore, compost made of MSW must be characterized before being used for agricultural soils. Copper and nickel in phytoavailable were effectively extracted with the strongest chelating agents used, HCl and Mehlich 3, probably because most metal is bound to organic matter in the compost. Cadmium, chromium, lead and zinc were no efficiently extracted with any of the tested extractants.

Disponibilidade de micronutrientes em cinco solos em função do tempo de incubação de um composto de lixo

The agricultural use of urban waste compost (WC) is an alternative for a better environmental-economic viability, because this organic residue is a source of nutrients and organic matter. This study was carried out in a greenhouse at the Brazilian Agricultural Research Corporation/National Soil Research Center. It had the objective of evaluating the effect of WC doses (0; 25; 50 and 100 Mg ha-1) and incubation periods (16; 32; 64 and 150 days) on micronutrients availability Cu, Fe, Mn and Zn by Mehlich-1, in Rio de Janeiro and Sao Paulo soils (Red-yellow Latosol, Red-yellow Podzol, Chernossolo Haplico Ortico, Planosol and Red Dusky Podzol). Most of the micronutrients had their availability reduced at the beginning of incubation, which was dependent of the texture, pH and organic matter content in the soil. Continued use of WC, mainly in the highest doses, and especially for the Mn and Zn, can result in risks of soil contamination, in periods more than 6 months with reduction of availability of the elements.