Comparative study of 3,4,3',4'-tetrachlorobiphenyl in male and female rats and female monkeys.

3,4,3',4'-Tetrachlorobiphenyl (TCB) is thought to be the most toxic chlorinated biphenyl present in commercial polychlorinated biphenyl (PCB) formulations. A comparative study of the distribution and excretion of TCB has been done in made and female rats and female rhesus monkeys in an effort to account for the toxicity of this PCB. The distribution and clearance of TCB were similar in male and female rats, and although TCB was cleared more slowly by monkeys than by rats, the monkeys were able to clear it at an appreciable rate so that tissue levels were negligible 6 wk after TCB administration. The results indicate that the toxicity of TCB cannot be attributed to inability of the animals to metabolize and excrete it or to its persistence in any tissue, with the possible exception of blood. TCB and/or TCB metabolites appear to be more persistent in blood than any PCB studied to date.