Changes in the carbonate ion concentration in seawater can affect the saturation state (and
hence biological availability) of several types of calcium carbonate (e.g., calcite, aragonite, or high - magnesian calcite.
In the absence of recent human interference in the biogeochemical cycle of aluminium the reaction of silicic acid with aluminium has acted as a geochemical control of
the biological availability of aluminium.
Studies suggest that selenium binds to mercury, potentially reducing
the biological availability of mercury, while n - acetyl - l - cysteine (NAC) promotes urinary excretion of methylmercury.
We have also learned that
the biological availability of certain protein sources actually determines how easy or difficult they are to metabolize.