Extraction and bioavailability of heavy metals in response to the addition of sewage sludge to the soil

Diante dos riscos ambientais relacionados ao uso agrícola de lodo de esgoto contendo metais foi realizado um experimento, com o objetivo de avaliar o efeito do lodo, combinado ou não com P, K e PK, sobre o acúmulo de metais na parte aérea das plantas e comparar a eficiência de extratores na fitodisponibilidade de metais. Amostras da camada de 0-20 cm de um Argissolo Vermelho Amarelo eutrófico foram transferidas para vasos e tratadas com doses equivalentes a 0, 10, 20, 30, 40 e 50 Mg ha-1 de lodo (base seca). Após 30 dias de incubação, determinou-se os teores de Fe, Mn, Cu, Zn, Cd, Ni, Cr e Pb (extraídos por HCl 0,1 mol L-1, Mehlich-3 e DTPA pH 7,3), procedeu-se aplicação de duas doses de P (0 e 100 mg kg-1) e duas dose de K (0 e 100 mg kg-1). Cultivaram-se plantas de milho (Zea mays L.) durante 50 dias, coletando-se a parte aérea para determinação de metais. A aplicação de lodo aumentou o teor de Fe, Mn, Zn e Cu no solo e o acúmulo pelas plantas, enquanto a complementação do resíduo com potássio aumentou a produção de matéria seca e diminuiu o acúmulo de Zn. A redução do pH e o Mn nativo do solo influenciaram no aumento da disponibilidade Mn. Todos os extratores foram eficientes para predição da fitodisponibilidade de Zn e Cu. Para o Mn e Fe, os mais eficientes foram: HCl e Mehlich-3, HCl e DTPA, respectivamente. Para os demais metais, os extratores se mostraram pouco eficientes.To evaluate environmental risk of sludge application in agriculture, a greenhouse experiment was carried out in Piracicaba, SP, Brazil, to compare the efficiency of extractors in the availability of heavy metals to plants, in soil treated with sewage sludge. The effect of the sludge was also evaluated combined or not with P, K and PK, on the accumulation of metals in the shoot. Soil samples, collected from the 0-20 cm layer of a Typic Hapludalf were placed in pots and mixed with 0, 10, 20, 30, 40 and 50 Mg ha-1 (dry-basis) of sludge. Thirty days after incubation, soil samples were taken from each pot for determination of Fe, Mn, Cu, Zn, Cd, Ni, Cr and Pb (extracted by HCl 0.1 mol L-1, Mehlich-3 and DTPA pH 7.3). Two Rates of phosphate as were applied (0 and 100 Mg ha-1) as well as two rates of potassium (0 and 100 Mg ha-1). Maize (Zea mays L.) plants were grown for 50 days, collected and submitted to heavy metal determination. The application of sewage sludge increased the amounts of Fe, Mn, Cu and Zn accumulated in plants, whereas the addition of potassium increased dry matter yield and decreased the accumulation of Zn. The pH reduction and soil native metal influenced the availability of Mn. All extractors were efficient in predicting the Zn and Cu availability to plants. For Mn and Fe the most efficient solutions were: HCl and Mehlich-3, HCl and DTPA, respectively. For the other metals, none of the extractors was efficient