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Environmental contextStudying the mechanism of binding between metals and natural organic matter is fundamental to understanding the transport and availability of these contaminants in the environment. The influence of sample treatment on the purification of organic matter showed significant differences in the interaction with metals. The results will contribute to improved modelling of metal binding to organic matter in soils, thereby providing a basis for a more realistic risk assessment. AbstractWe studied the changes in metal binding characteristics of extracted humic acids induced by HF/HCl treatment followed by dialysis, i.e. the last step of the International Humic Substances Society (IHSS) extraction protocol. We performed metal binding experiments with both the alkaline-extracted material (AE) and the fully purified (FP) humic acid using the electrochemical stripping technique (AGNES) and modelled the results using the NICA-Donnan model. The results showed an increase of free Zn, Cd and Pb concentrations of ~1 order of magnitude for the AE compared with the FP. These differences may be mostly explained by the different carbon content (51.3 % FP and 36.5 % AE) associated with an AE/FP carboxyl ratio of 0.5. Simulations using the NICA-Donnan model showed that halving the amount of carboxylic groups (Qmax,1) for the FP reduced this difference to 0.25 log units for Cd and Zn and to 0.15 log unit for Pb. There is a clear need for further research on the differences between purified v. less-disturbed natural organic material, which will contribute to improved modelling of metal binding to organic matter in soils, hence providing a basis for a more realistic risk assessment.

Environmental contextThe environmental behaviour of trace metals in soils and waters largely depends on the chemical form (speciation) of the metals. Speciation software programs combining models for the binding of metals to soil and sediment constituents are powerful tools in environmental risk assessment. This paper describes a new combination of speciation software with a fitting program to optimise geochemical model parameters that describes proton and metal binding to humic substances. AbstractHere we describe the coupling of the chemical speciation software ORCHESTRA with the parameter estimation software PEST. This combination enables the computation of optimised model parameters from experimental data for the ion binding models implemented in ORCHESTRA. For testing this flexible tool, the NICA-Donnan model parameters for proton-, Cd- and Zn-binding to Laurentian fulvic acid were optimised. The extensive description of the method implementation and the examples provided facilitate the use of this tool by students and researchers. Three procedures were compared which derive the proton binding parameters, differing in the way they constrain the model parameters and in the implementation of the electrostatic Donnan model. Although the different procedures resulted in significantly different sets of model parameters, the experimental data fit obtained was of similar quality. The choice of the relation between the Donnan volume and the ionic strength appears to have a strong influence on the derived set of optimal model parameters, especially on the values of the protonation constants, as well as on the Donnan potential and Donnan volume. Optimised results are discussed in terms of their physico-chemical plausibility. Coherent sets of NICA-Donnan parameters were derived for Cd and Zn binding to Laurentian fulvic acid.

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Recebido em 11/7/08; aceito em 13/4/09; publicado na web em 17/9/09 CHARACTERIZATION OF SLUDGE GENERATED IN WATER TREATMENT PLANTS: PROSPECTS FOR AGRICULTURAL APPLICATION. The work reported here involved the characterization of sludges produced at water treatment plants in Jaboticabal-SP using FeCl 3 as flocculant, and in Taquaritinga-SP and Manaus-AM using Al 2 (SO 4 ) 3 as flocculant. An evaluation was also made of the interaction of organic matter extracted from the sludges with different metal species. The results indicated that all the sludges produced at water treatment plants have an important agricultural potential and that their use depends on the characteristics of the raw water and the type of flocculant employed in conventional treatment. The humic substances extracted from the sludges showed different affinities for metal species, favoring eventual exchanges between potentially toxic metals and macro-and micronutrients. An alternative for the use of sludge in agriculture is to pretreat it to remove potentially toxic metals and enrich it with micro-and macronutrients that can be released to the plant.Keywords: humic substances; WTP sludge; agricultural. INTRODUÇÃOA potabilização das águas naturais para fins de abastecimento público tem como principal função adequar a água bruta afluente à estação ao padrão de potabilidade vigente estabelecido pela Portaria 518 de 25 de Março de 2004.1 O tratamento de água consiste basicamente na remoção de partículas suspensas e coloidais, matéria orgânica, micro-organismos e outras substâncias possivelmente deletérias à saúde humana presentes nas águas. 2Existem no Brasil cerca de 7.500 estações de tratamento de água (ETAs) e aproximadamente 75% destas, utilizam processo denominado convencional para tratamento da água. Este consiste em operações de coagulação, floculação (as quais utilizam sulfato de alumínio e/ou cloreto férrico como floculantes), decantação e filtração para a clarificação da água, seguida de correção de pH, desinfecção e, em alguns casos, de fluoretação. 2,3Na etapa de floculação e decantação é gerado um resíduo rico em matéria orgânica, micro e macro-nutrientes e metais potencialmente tóxicos, denominado lodo de estação de tratamento de água (LETA).4 Durante anos, o destino deste material vinha sendo os próprios mananciais de captação, agregando a estes uma elevada carga poluidora.3 A NBR 10.004/87 e a Lei Estadual de São Paulo 12.493/92 restringem e, até mesmo, proíbem essa prática, sugerindo que esses lodos devam ser reciclados e/ou reutilizados. Recentemente a fiscalização se tornou mais efetiva e as ETAs devem reutilizar esses lodos.Diversas alternativas econômicas e tecnicamente viáveis, além de ambientalmente vantajosas para o destino final desse resíduo têm sido propostas, como disposição em aterros sanitários, uso na formação de biosólido, 3 emprego na construção civil 5-7 e aplicações industriais diversas. [8][9][10][11][12][13][14] Uma das possibilidades de reutilização do LETA é seu emprego como aditivo em setores agrícolas. Por ser ri...

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A capacidade de complexação de substâncias húmicas extraídas de amostras de turfa coletadas na região do Rio Mogi em Ribeirão Preto, SP, Brasil, foi determinada utilizando Al(III), Pb(II), Cr(VI) e Cd(II). A seguinte ordem de afinidade foi observada: Cr(VI)< Cd(II)