Combining Drosophila melanogaster somatic-mutation-recombination and electron-spin-resonance-spectroscopy data to interpret epidemiologic observations on chromium carcinogenicity.

Lung cancers are significantly increased among workers exposed to chromate (Cr6+, Cr3+), chromium pigments (Cr6+) and chromium plating (Cr6+). Chromium lung burdens and cancer risk increase proportionately with duration of employment at long latencies. However, this epidemiologic information alone is insufficient in determining whether Cr6+ or Cr3+ are equally important in causing cancer. We have attempted to combine epidemiologic data with data from the Drosophila melanogaster somatic-mutation-recombination-test and from the in vitro electron-spin-resonance spectroscopy study to demonstrate that following somatic recombination plays a more important role than somatic mutation in chromium carcinogenesis. Cr4+ is more important than Cr5+ or Cr6+ in inducing somatic recombination while Cr6+ produces more and bigger clones than Cr4+ in somatic mutation. Cr3+ produces negative results in this fruit-fly wing-spot-assay. When the larvae and flies exposed to Cr6+ and Cr4+ are examined by ESR, only Cr5+ and Cr3+ are found. Thermodynamic parameters deltaE, deltaH, and deltaS are also estimated from these latter experiments to explain the relative importance of Cr6+, Cr4+, Cr3+ in chromium carcinogenesis among exposed industrial workers.