Indicators of matrix dependent variation in effective dose for chromium and nickel aerosol exposures

Inhaled particulates containing Cr and Ni are partially cleared or dissolved thus contributing to short-term internal exposures and partial retention in airways and airspaces. The retained fraction may continuously contribute to internal exposure after external exposure has ceased, through intra- and extracellular chemical processes which continuously liberate various metallic species; i.e. via an active deposit. Recent experiments with Ni and Cr compounds, and freshly produced welding fumes, which contain Ni and Cr, demonstrate a strong dependence of the distribution of these metals on oxidation state, solubility, bioavailability and toxicity as measured by in-vitro bioassay, depending on the collection, storage and analytical technique. It is suggested that exposure limits must consider the wide variation in short- and long-term delivered dose of toxic metals to target tissue with matrix, and that current protocols may be inadequate to protect workers in different industries involving exposures to widely different types of aerosols having only the same chemical element in common.