Laser ablation ICP-MS analysis of incremental biological structures: archives of trace-element accumulation

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Abstract
Incremental growth layers occur in the hard structures of many types of organisms (tree xylem, mollusc shells, vertebrate teeth, otoliths, scales, etc.). Microprobes have previously shown that these layers contain archival information about an organism's chemical environment. However, trace elements, including metals, are generally undetectable with these instruments. A relatively new technique, laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) promises multielement analytical capability with extremely low detection limits (conservatively, <1 ppm), combined with very fine spatial resolution (down to 30–100 μm beam diameter). Fish otoliths and vertebrate tooth cement and dentin offer the greatest potential for retrieving element archival information, because they are not subject to resorption, and reflect the organism's exposure to or accumulation of trace elements from the ambient environment. Other structures are less promising, because they exhibit element mobility between growth layers (tree rings), or are subject to metabolic turnover and resorption (scales, bones, shells). While the LA-ICP-MS technique is novel in the biological sciences, the few studies available indicate that reproducible, year-by-year data on metal accumulation or exposure will probably be retrievable from many types of incremental structures. The main problem currently is the lack of solid standard reference materials which match the physicochemical properties of hard biological tissues.Key words: laser ablation, mass spectrometry, trace metals, environmental pollution, calcified tissues.