Microbial infestation: a pathway of fluorine enrichment in bone apatite fragments (Negev phosphorites, Israel)

Backscattered electron (BSE) imaging and electron probe-coupled analysis of bone debris in the Negev phosphorites (Israel) show that F concentrations vary considerably in these components, and that these variations are driven by microbial activity. The bone debris are microbially tunneled, commonly with a micritic carbonate fluorapatire (CFA) phase filling the tunnels and gradually replacing the bone matrix. As a rule, the micritic CFA within the microbial tunnels is significantly much more F-enriched (F/P2O5-0.106-0.12 5) than the bone matrix (F/P2O5-0.083-0.104). Similar results are obtained in bones at final stages of microbial infestation and micrite phosphate rep lacement. The infested-replacing envelope invading the bone debris is much F enriched (enrichment factor of about 1.27 on average) than the surviving bone that escaped boring. These results are explained by redeposition as CF A of the microbially bored and dissolved hydroxyapatite, presumably fostere d by microbial F transfer from porewaters to the sites of CFA precipitation in bone microborings. This pathway of F-enrichment driven by microbial act ivity may also explain the enigmatic differential U-enrichment previously o bserved in Negev phosphorite bones. (C) 2000 Elsevier Science B.V. All righ ts reserved.