Intra-ring variability of Cr, As, Cd, and Pb in red oak revealed by secondary ion mass spectrometry: Implications for environmental biomonitoring

Reconstructing the history of ambient levels of metals by using tree-ring c hemistry is controversial. This controversy can be resolved in part through the use of selective microanalysis of individual wood cells. Using a combi nation of instrumental neutron activation analysis and secondary ion mass s pectrometry. we have observed systematic inhomogeneity in the abundance of toxic metals (Cr, As, Cd, and Pb) within annual growth rings of Quercus rub ra (red oak) and have characterized individual xylem members responsible fo r introducing micrometer-scale gradients in toxic metal abundances. These g radients are useful for placing constraints on both the magnitude and the m echanism of heavy metal translocation within growing wood. It should now be possible to test, on a metal-by-metal basis, the suitability of using tree -ring chemistries for deciphering long-term records of many environmental m etals.