MICRO-SPATIAL VARIATIONS OF HEAVY-METALS IN THE TEETH OF WALRUS AS DETERMINED BY LASER-ABLATION ICP-MS - THE POTENTIAL FOR RECONSTRUCTING AHISTORY OF METAL EXPOSURE

This study explored the possibility of using laser ablation inductivel y-coupled plasma-mass spectroscopy to measure trace metals and other e lements within the annual growth layers of the teeth of walrus harvest ed from the Canadian Arctic. Using sample ablation ''footprints'' of 1 25 mu m diameter on transects across the exposed cross-sections of tee th, this technique detected Pb, Cu, Zn and Sr, but not Cd, in tooth ce mentum. The micro-spatial patterns of elements were consistent among d ifferent transects on the same tooth, and revealed subtle differences between animals of different ages. The youngest walrus in the sample ( 4 yr) contained higher concentrations of Pb and Cu than older animals in the growth layer deposited during the first year of life, while the oldest animal (33 yr) exhibited higher Pb and Zn than younger animals in the outer layer corresponding to the year 1988. The differences be tween animals and across annual layers may reflect both life history a nd metal exposure phenomena, including high amounts of metals transfer red from mothers to pups in maternal milk. The ability to detect metal s in a repeatable fashion within annual growth layers suggests that me tal exposure histories accurate to within a year might be re-construct ed for the lifetimes of long-lived animals, and that a series of such individual studies would allow exposure histories covering centuries t o be quickly assembled. These data may suggest the most likely explana tion for the currently high levels of some metals observed in certain Arctic marine mammals, i.e., natural phenomenon or anthropogenic conta mination.