Mineral bioavailability behavior

Phenomena such as chemical and biological transformations, metal mobility, bioavailability, bioaccumulation, toxicity, and persistence in the environment frequently depend on the chemical form or speciation of a given ion, especially the metallic ions. For example, there is normally a great difference between the sorption behavior of a free metal cation and that of its anionic complexes onto mineral oxides and hydroxides. 

In addition to complexing metals in the aqueous phase, humic materials can also remove metals and radionuclides contained within the mineral matrix (18). The factors that control this behavior are not well understood however, it has direct implications on waste storage and containment strategies. The binding of organic and inorganic contaminants to humic substances is known to alter their bioavailability (41). Organic contaminants that are associated with humic substances are essentially unavailable for uptake by biota. In most cases studied, toxic metals associated with humic materials also have reduced uptake. With the new focus on bioremediation of polluted are as, the effect of the association of pollutants with humic materials on their phytotoxic properties must be considered, particularly for bound metals and radionuclides. 

In sulfate-dominated wetlands, production of sulfide (through biological reduction of sulfate) and formation of ferrous sulfides may preclude phosphorus retention by ferrous iron in regulating phosphorus bioavailability (Caraco et al., 1991). In iron- and calcium-dominated systems, Moore and Reddy (1994) observed that iron oxides likely control the behavior of inorganic phosphorus under aerobic conditions, whereas calcium phosphate mineral precipitation governs the solubility under anaerobic conditions. This difference is in part due to a decrease in pH under aerobic conditions as a result of oxidation of ferrous iron compounds, whereas an increase in pH occurs under anaerobic conditions as a result of reduction of ferric iron compounds. The juxtaposition of aerobic and anaerobic interfaces promotes oxidation-reduction of iron and its regulation of phosphorus solubility. 

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