Metal Flux and Dynamic Speciation at (Bio)interfaces. Part I:  Critical Evaluation and Compilation of Physicochemical Parameters for Complexes with Simple Ligands and Fulvic/Humic Substances

Abstract

In the computation of metal flux in aquatic systems, at consuming surfaces like organism membranes, diffusion processes of metal ions, ligands, and complex species, as well as the kinetic and thermodynamic aspects of their chemical interactions, must be considered. The properties of many natural ligands, however, are complicated (formation of successive complexes for simple ligands, polyelectrolytic properties and chemical heterogeneity for macromolecular ligands, large size distribution and fractal structure for suspended aggregates). These properties should be properly modeled to get the correct values of the chemical rate constants and diffusion coefficients required for flux computations. The selection of the most appropriate models and parameter values is far from straightforward. This series of papers discusses the various models and compiles the parameters needed for the three most important types of complexants found in aquatic systems: the small, simple ligands, the fulvic and humic compounds, and the colloidal "particles" or aggregates. In particular, new approaches are presented to compute the rate constants of metal complex formation, with both fulvics/humics and particles/aggregates. The method to include the site distribution of fulvics/humics and the size distribution of particles/aggregates in metal flux computation at consuming interfaces is also discussed in detail. These models and parameters are discussed critically and presented in the same framework, forthe computation of metal flux in presence of any of the above complexants or mixtures. Such parameters, largely spread in the literature, are gathered here and selected specifically for environmental applications. The focus in Part I of the series is on simple ligands and fulvic/humic compounds. Part II deals with particulate and aggregate complexants.

When are metal complexes bioavailable?

“…As seen above, our knowledge with respect to metal bioavailability has greatly evolved over the past 25 years, progressing largely (but not entirely) from equilibrium concepts that mainly considered the contribution of the free ion [1] to dynamic systems where several factors, including the intrinsic properties of the metal and ligand, [34,80] their respective concentrations, organism characteristics such as size, [64,81] media properties and the kinetic behaviour of the metal-ligand system [78,82] are considered. In many cases, equilibrium models are a reasonable simplification of the real-world system, such that simple relationships should be obtained that relate metal speciation to biological effects.…”

Climate Change Impacts on Sediment Quality of Subalpine Reservoirs: Implications on Management

“…In fact, the direct relation to fine sediments (<2 mm) and TOC indicates that ligands can influence their distribution. The inverse relation to depth confirms that their fate is largely conditioned by the presence of natural simple or complex ligands (like fulvic and humic compounds) and colloidal particles [62][63][64].…”

A theoretical and experimental study of calcium, iron, zinc, cadmium, and sodium ions absorption by aspartame

“…This fact shows that there was a low drift in the total energy during MD simulations and that the simulation times were sufficient and stable under convergence conditions. The computational and experimental diffusion coefficients [46] of all ions are shown in Table 2. As shown, in spite of the simplicity of the water model and the small number of ions, the simulation of the Brownian motion of the ions is realistic and theoretical and experimental diffusion coefficients are compatible.…”