Arsenic contamination in groundwater: some analytical considerations.

For countries such as Bangladesh with a significant groundwater arsenic problem, there is an urgent need for the arsenic-contaminated wells to be identified as soon as possible and for appropriate action to be taken. This will involve the testing of a large number of wells, potentially up to 11 million in Bangladesh alone. Field-test kits offer the only practical way forward in the timescale required.

Modeling the interactions between humics, ions, and mineral surfaces.

Model VI and the NICA-Donnan model are two successful models presently available for describing metal ion binding by humic materials. Both models deal with the complexity of the underlying processes (intrinsic heterogeneity, partial correlation between affinity distributions, variable stoichiometry, electrostatics) in a pragmatic way. The parameters of the NICA-Donnan model and their determination are discussed.

Codeposition of organic carbon and arsenic in Bengal Delta aquifers.

We present data showing that arsenic (As) was codeposited with organic carbon (OC) in Bengal Delta sediments as As and OC concentrations are highly (p < 0.001) positively correlated in core profiles collected from widely dispersed geographical sites with different sedimentary depositional histories. Analysis of modern day depositional environments revealed that the As-OC correlations observed in cores are due to As retention and high OC inputs in vegetated zones of the deltaic environment.

Predominance and mineral stability diagrams revisited.

Predominance and mineral stability diagrams are most useful if they are based on a full chemical speciation. The diagrams can then include a wide range of reactions of importance in environmental chemistry including adsorption and ion exchange reactions. They can also take into account the possible interactions between a large number of components and are able to model changes at a fixed total concentration of each component rather than under the commonly used but less realistic assumption of a fixed activity.

Generic NICA-Donnan model parameters for metal-ion binding by humic substances.

A total of 171 datasets of literature and experimental data for metal-ion binding by fulvic and humic acids have been digitized and re-analyzed using the NICA-Donnan model. Generic parameter values have been derived that can be used for modeling in the absence of specific metalion binding measurements. These values complement the previously derived generic descriptions of proton binding.