A coplanar polychlorinated biphenyl (PCB) when eaten by test animals i
ncreased the rate of recombination in somatic cells, indicating a new
mechanism of action for these compounds. Using the eye-mosaic test a h
igh bioactivation strain of Drosophila that consumed 4,4'-dichlorobiph
enyl (4,4'-DCB) manifested a genotoxicity rate that was three-fold gre
ater than that in animals fed the solvent-spiked medium. This compound
was not genotoxic in a suppressed bioactivation strain indicating tha
t genotoxicity requires bioactivation of the compound. High bioactivat
ion test strains made heterozygous for a paracentric inversion, a chro
mosomal rearrangement that suppresses homologous recombination, exhibi
ted significantly reduced genotoxicity after treatment.