Naturally occurring apatite as a source of orthophosphate for growth of bacteria and algae.

Several naturally occurring calcium-phosphate apatites which varied in crystalline structure and ionic composition were added as crystals of different particle size to P-free (<1μg/liter total P) nutrient media. Sufficient ortho-PO 4 (3-) was released by the partial dissolution of apatite crystals at limnetic pH levels (pH 7.8) to support growth of several unialgal-mixed bacterial cultures. The biomass produced by mixed populations increased as the amount of available apatite was increased and as the pH of the media and the particle size of the apatite crystals were decreased. These findings suggest that although apatite characteristically displays reduced solubility under alkaline conditions, the tons of apatite which are continuously entering aquatic environments as erosion material may be contributing to the P loading of those ecosystems.