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

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 ΔE, ΔH, and ΔS are also estimated from these latter experiments to explain the relative importance of Cr⁶⁺, Cr⁴⁺, Cr³⁺ in chromium carcinogenesis among exposed industrial workers.