Aplicações de técnicas espectroscópicas e polarográficas para caracterização e avaliação da reatividade do húmus com o herbicida atrazina. / Application of spectroscopic and polarographic methods to characterize and evaluate the reactivity between humus and atrazine.

AUTOR(ES)

Marcelo Luiz Simões

DATA DE PUBLICAÇÃO

1999

RESUMO

One alternative to disposal of urban residues is recycling through composts and earthworm composts (humus production). The absence of a quality standard of these materials however brings limitations to commercial development with damage to producers and consumers. In this work was proposed a strategic parameter to be used as standard. From Electron Paramagnetic Resonance (EPR) analysis samples of humus with level semiquinone free radicals of 1017 spin/g of sample and 1018 spin/g of carbon, or higher, indicated good quality of product, with adequate humification degree. Also were studied mechanisms of interaction between humus and the herbicide Atrazine (AT). The proposal was evaluate potential of AT sorption by humus and possible catalytic effect in the degradation and photodegradation of this herbicide. Data from Ultraviolet and Visible Spectroscopy (UV-Vis) showed that for pHs close to AT pKa (1.68) the humus showed catalytic effect in degradation of AT similar as those observed in literature with purified humic and fulvic acids. However for neutra1 pHs AT degradation was not observed even in the presence of high humus concentrations and long periods of interaction (262 days). Using Differential Pulse Polarography (DPP), combined with data of UV-Vis Spectroscopy, an AT sorption curve on humus was obtained showing a maximum value of 20% around pH 4.0, decreasing for less than 5% of sorption for other pHs analyzed (2.0; 6.0; 7.0; 8.0 and 10.0). Data from EPR gave no evidence of electron transfer reaction. So from the kind of sorption curve, obtained by DPP, the major mechanism of reaction between AT and humus was suggested to be hydrophobic bonding. Experiments of AT photodegradation using UV-Vis light (300-450 nm) showed larger efficiency of the process in the presence of the humus. This occurred probably due action of photo-oxidants on AT, originated from excitation of humus by the UV radiation. It was also observed, dependence with the humus concentration, and in the range 10 to 1800 mg.L-1 there was larger photodegradation of the AT for values around 300 mg.L-1.

ASSUNTO(S)

humus espectroscopia spectroscopy polarografia atrazina polarography atrazine húmus

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