Abstract
ABSTRACTBiogenic hydroxyapatite (bio-HA) has the potential for radionuclide capture and remediation of metal-contaminated environments. Biosynthesis of bio-HA was achieved via the phosphatase activity of a Serratia sp. supplemented with various concentrations of CaCl2 and glycerol 2-phosphate (G2P) provided at pH 7.0 or 8.6. Presence of hydroxyapatite (HA) was confirmed in the samples by X-ray powder diffraction analysis. When provided with limiting (1 mM) G2P and excess (5 mM) Ca2+ at pH 8.6, monohydrocalcite was found. This, and bio-HA with less (1 mM) Ca2+ accumulated Eu(III) to ∼31% and 20% of the biomineral mass, respectively, as compared to 50% of the mineral mass accumulated by commercial HA. Optimally, with bio-HA made at initial pH 7.0 from 2 mM Ca2+ and 5 mM G2P, Eu(III) accumulated to ∼74% of the weight of bio-HA, which was equal to the mass of the HA mineral component of the biomaterial. The implications with respect to potential bio-HA-barrier development in situ or as a remediation strategy are discussed.
Highlights
Anthropogenic radionuclides are responsible for contamination of a range of environments as a result of nuclear activities
With Biogenic hydroxyapatite (bio-HA) made at initial pH 7.0 from 2 mM Ca2C and 5 mM glycerol 2-phosphate (G2P), Eu(III) accumulated to »74% of the weight of bio-HA, which was equal to the mass of the HA mineral component of the biomaterial
40-mM G2P was provided to samples A and D over the period of 8 days (Table 1), negligible residual inorganic phosphate (Pi) was found in the solutions
Summary
Anthropogenic radionuclides are responsible for contamination of a range of environments as a result of nuclear activities. A deep GDF, while containing potential nutrients, would comprise an extreme environment with stresses to the local biota including, in addition to high radiation, highly alkaline waters arising from contact with cementitious material used as backfilling around steel containers containing stored waste (Berner 1992). An alkali degradation product of cellulose, isosaccharinic acid (ISA) in addition to chelating agents like EDTA and nitrilotriacetic acid (used in decontamination processes) presents available nutrients for alkaliphilic bacteria; these compounds, if allowed to persist, would complex with radionuclides and assist their mobility (Bassil et al 2015; Bouchard et al 2006; Glaus and Van Loon 1999; Van Loon and Glaus 1997). The pH will fall with time and distance from the GDF; the formation of barriers to local, as well as wider nuclide dispersion at less extreme alkaline pH, as well as in neutral environments in other situations like the FDNPP, or in groundwaters, should be considered
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