Dynamics of potencially toxic metals in soil after sewage sludge application / Dinamica de metais potencialmente toxicos no solo apos aplicação de lodo de esgoto

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The present research aims at studying the dynamics of six potentially toxic metals ? Cd, Cr, Cu, Ni, Pb and Zn ? on a clay loam soil, where sewage sludge was incorporated in a single application. The soil under analysis was contained in six fiberglass prototypes (1.2 m high x 1.0 m in diameter); inside each prototype, free-drainage collectors were installed at 0.25, 0.50, 0.75 and 1.0 meter deep to collect leachate. The prototypes had received during 20 months regular applications from sludge in previous research, remaining in rest for 20 months more, until its use in the present research. Three sludge application rates were adopted (dry basis) in soil that had no application of lime ? 100, 67 and 33 t ha-1 ? and one in soil with lime application ? 67 t ha-1. The lime had been applicated in previous studies. The analysis of the soil before the new sludge incorporation revealed the influence of applications performed 20 months earlier; when comparing with the control prototypes, we found lower pH values, higher levels of organic matter and electric conductivity of the saturated stratum in the superficial layers, and higher real acidity in the prototypes without lime. Higher CEC values were found only in the 0 to 0,05-m soil profile in those soils that had lime application. With the sludge incorporation, that presented acid conditions, the level of pseudo-total metals in the soil significantly increased in the 0 to 0,05-m profile, in proportion to the percentage of organic matter in the soil. The analysis of the metal bioavailability percentage showed that the commonest decreasing sequence for HCI extraction was Zn = Cu = Pb >Cr, whereas the commonest sequence for DTPA was Zn >Cu >Pb = Cr. In the analysis for HCL, the rate of 33 t ha-1 was considered the most adjusted for an application of sludge with agricultural ends, while in the extration for DTPA the three application rates can be used in agriculture. With regard to sequential extraction, Zn appeared mostly in soluble and exchangeable form, whereas Cr was mostly found in the form of insoluble precipitates; Pb showed greater affinity with organic matter, being found both in soluble and insoluble form, depending on the pH of the soil and the predominant fraction of humus in the organic matter; Cu appeared linked to organic matter in the soil and in the form of insoluble precipitates; Ni was found in the prototype with higher sludge application rate, present in the reducible fraction; Cd was not detected in the soil. The study of metal mobility in soil only revealed the mobility of zinc, even at an acid pH level; this metal was found in layers up to 0,50 m deep

ASSUNTO(S)

heavy metals metais pesados quimica do solo lodo de esgoto soil chemistry sewage sludge

ACESSO AO ARTIGO

Documentos Relacionados