Manganese bioavailability

In order to determine the independent effect of cellulose on manganese bioavailability, manganese tolerance tests were administered with 15 g of alpha cellulose (Sigma Co., Inc., St. Louis, MO) to six human subjects. The cellulose was given in gelatin capsules in addition to a 40 mg dose of manganese as MnCl. and 200 ml of deionized water. As seen in Figure 4, the addition of cellulose to... 

Soil pH affects the transformation of Cr between Cr(III) and Cr(VI) in soils. Since Cr(VI) has greater bioavailability and mobility in soils than Cr(III), which is strongly bound by soil solid matrix (Han and Banin, 1997). Cr(III) can be oxidized by soil manganese oxides into Cr(VI), while Cr(VI) can be reduced by organic matter, Fe(II) and microorganisms in soils. Reduction of Cr(VI) has been found to occur much slower in alkaline soils compared to acid soils (Cary et al., 1997). 

In Limnodrilus sp., an oligochaete worm, copper bioavailability from surhcial freshwater sediments is associated with the amount of copper present in the manganese oxide fraction of the sediment. The redox potential and pH in the gut of Limnodrilus allows the dissolution of the manganese oxide coating, making copper and other metals available for uptake (Diks and Allen 1983). 

The first consideration was the speciation and distribution of the metal in the sediment and water. Benthic organisms are exposed to surface water, pore water and sediment via the epidermis and/or the alimentary tract. Common binding sites for the metals in the sediment are iron and manganese oxides, clays, silica often with a coating of organic carbon that usually accounts for ca. 2% w/w. In a reducing environment contaminant metals will be precipitated as their sulfides. There is not necessarily a direct relationship between bioavailability and bioaccumulation, as digestion affects the availability and transport of the metals in animals, in ways that differ from those in plants. 

In discussing nickel exposure, it is important to consider what form of nickel a person is exposed to and its bioavailability. Such information is not often available. Although high concentrations of nickel may be found in contaminated soil and sediment, it may be embedded in a crystalline matrix or bound to hydrated iron, aluminum, and manganese oxides and, therefore, not bioavailable. 

Nutritional Bioavailability of Manganese Kies, C., Ed. ACS Symposium Series 354 American Chemical Society Washington, DC, 1987. 

Manganese was readily bioavailable in seawater at the time of the evolution of photosynthesis (about 3 X 109 years ago) and now abounds on the sea bottom in the form of oxidic manganese nodules with about 20 per cent Mn content. 

Cobalt is well known as having its bioavailability controlled by manganese oxides (Jarvis, 1984). 

A wide range of research publications has identified various soil properties and their potential influence on substance behavior. Soil properties such as organic matter, iron, manganese, and aluminum (hydro)oxide concentrations, cation exchange capacity, and pH can all affect the bioavailability, form, and toxicity of substances. 

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