Evaluation of diffusive gradients in thin films technique (DGT) for measuring Al, Cd, Co, Cu, Mn, Ni, and Zn in Amazonian rivers

Programa de Pós-Graduação em Geociências e Meio Ambiente, Instituto de Geociências e Ciências Exatas - IGCE, Universidade Estadual Paulista - UNESP, Avenida 24-A, 1515, 13506-900, Rio Claro, São Paulo, Brazil.
Environmental Monitoring and Assessment (Impact Factor: 1.68). 09/2013; 186(2). DOI: 10.1007/s10661-013-3430-x
Source: PubMed


Studies concerning the lability and bioavailability of trace metals have played a prominent role in the search for contamination of water resources. This work describes the first application yet of the diffusive gradients in thin films technique (DGT) to the determination of the fraction of free plus labile metals in waters from the Amazon Basin. Due to the complexity of the use of DGT for samples with low ionic strength and high organic matter content (characteristic of Amazonian rivers), a new analytical procedure was developed. The method is based on the determinations of apparent diffusion coefficients (Dap) in the laboratory, by performing deployments in samples collected in the corresponding sites of study. The Dap thereby determined is then used for in situ measurements. The suitability of the proposed approach for determination of labile Al, Cd, Co, Cu, Mn, Ni, and Zn in the Amazon River and Rio Negro (English: Black River) was evaluated. Except for Co, Mn (in a deployment at Rio Negro), Ni and Zn (in a deployment at Amazon River), labile in situ measurements were lower or similar to dissolved concentrations, indicating suitability of the proposed approach.

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    ABSTRACT: Gaining insight into the physicochemical processes integrated in a DGT (diffusion gradients in thin films) measurement and combining them in a model can assist in retrieving fundamental information, both qualitative and quantitative, on the probed system. New experiments (such as varying the thicknesses of the gel or the resin layer) and their mathematical treatment to extract meaningful parameters have been suggested from theoretical considerations. The concept of lability degree is useful in describing an interpretation of the DGT concentration as the summation of the free metal concentration plus the labile fraction of all complexes multiplied by a ratio of diffusion coefficients. In some cases, the lability degree can be directly estimated with specific measurements and a very simple expression. We review the current status of these interpretations, including numerical simulations, with special focus on analytical expressions, because they can be more accessible to the standardDGTpractitioner. Present limitations and challenges for future work in DGT interpretation are also discussed.
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