Biomineralization studies of a recently discovered 2,000-year-old bronze sculpture may help modern scientists understand how to prevent metal corrosion, discover the safest ways to permanently store nuclear waste, and understand other perplexing problems. [Lyons et al., Cryst. Growth Des., DOI: 10.1021/cg900402b].
Best known as "The Scraper," the statue of Apoxyomenos depicts the athlete scraping sweat and dust from his body with a small curved instrument and may prove the answer to many unanswered questions surrounding biomineralisation, which is the process by which animals and plants use minerals from their surroundings and form shells and bone. Apoxyomenos was encrusted with such deposits. Both the long-term influence of the bronze material of the sculpture on the biomineralization process and mineral composition of marine organisms and the effects of attached calcareous structures on the reduced deterioration of the sculpture surface were analysised.
Studies of samples from Apoxyomenos by inductively coupled plasma atomic emission spectroscopy analysis showed all samples to have a high metal content, with the specific metals and their concentrations being consistent with the sculpture as the source rather than normal seawater. No metal-based crystalline phases were found by powder X-ray diffraction apart from the presence of iron and copper hydroxides in one sample that showed a distinctly green coloration. X-ray diffraction analysis indicated that calcite, magnesium calcite, and aragonite were the dominant phases in all cases, with minor or trace phases of albite, microcline, and mineral quartz. The phase compositions of these biomineralized structures were significantly different from those of the same organisms living in unpolluted environments. The accumulation of non-native metals in the calcareous structures of these organisms and the unusual phase compositions of the latter suggest metal-induced changes to the biological pathways controlling the transport of calcium and magnesium and incorporation of heavy metals at inorganic matrix growth sites.
The level of heavy metal incorporation in the inorganic matrices and the changes to the crystallographic phase content, in spite of the organisms not being in direct contact with the surface, have shown the sequestration abilities of these organisms and the impact of metal uptake on the metabolic pathways used in biomineral formation.
More detailed studies need to be carried out to resolve the mechanisms controlling trace element incorporation before biomineralization can provide broader benefits in diverse areas including paleoclimatic and ecological studies, as bioindicators in environmental monitoring, and in corrosion mitigation and nuclear waste storage strategies.