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Research Project: Integrated Field Scale Management Systems for the Use of Degraded Waters

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Title: Modeling selenium (IV and VI) adsorption envelopes in selected tropical soils using the constant capacitance model

Author
item GABOS, MARIANA - Universidad De Sao Paulo
item Goldberg, Sabine
item ALLEONI, LUIS - Luiz De Queiroz College Of Agriculture (ESALQ)

Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2014
Publication Date: 8/7/2014
Citation: Gabos, M.B., Goldberg, S.R., Alleoni, L.R.F. 2014. Modeling selenium (IV and VI) adsorption envelopes in selected tropical soils using the constant capacitance model. Environmental Toxicology and Chemistry. 33(10):2197-2207.

Interpretive Summary: Selenium is a trace element that is toxic to animals at elevated concentrations. Toxic concentrations can occur in agricultural soils and irrigation waters. A better understanding of the adsorption behavior of this ion is necessary. Adsorption of selenate and selenite by 15 Brazilian soils was investigated under changing conditions of solution pH. The adsorption behavior was evaluated and described using a chemical surface complexation model. Our results will benefit scientists who are developing models of selenium movement in soils. The results can be used to improve predictions of selenium behavior in soils and thus aid action and regulatory agencies in the management of soils which contain elevated concentrations of selenium.

Technical Abstract: The adsorption of selenium (Se) on soil is important due to the relevance of Se to environmental and health issues. The adsorption of Se(IV) and Se(VI) was evaluated on soil samples from São Paulo state, Brazil, as a function of varying pH, and the experimental data were fitted to the constant capacitance model (CCM). Adsorption experiments were conducted for 15 soil samples, after the addition of 20 µmol L/1 of either Se(IV) or Se(VI), and the adjusted pH ranged between 2.5 and 10. Se(IV) adsorption was high for all soils, decreased with increasing pH and, was strongly correlated to Fe and Al oxide contents. On the other hand, Se(VI) adsorption was very low at pH values commonly found in agricultural soils, except for the highly weathered Rhodic Acrudox. The CCM fitted the Se(IV) and Se(VI) adsorption data well. Optimizations of mono and bidentate complexation and surface protonation constants were used for the Se(IV) adsorption data. For Se(VI), optimizations for the two monodentate species were employed.