Distribution of polychlorobiphenyls in pregnant mice and fetuses on various days of gestation.

14C-2,4',5-trichlorobiphenyl (test series A) and a laboratory mixture of 14C-PCBs, which in addition to 2,4',5-trichlorobiphenyl, contained dichlorobiphenyl and other trichlorobiphenyl isomers (test series B), were administered orally to pregnant mice on the 13th, 15th and 17th day post conceptionem (p.c.), respectively. The development of the fetuses was accompanied by increasing activity concentrations and changes in the distribution patterns of the radioactive PCBs (and/or metabolites). In either test series, one day after administration the 18-day old fetus showed approximately a 2.5 times higher activity concentration than the fetus of an earlier developmental stage (14th day p.c.). Considering the weight gain, the quantity of activity per fetus increased almost tenfold. PCBs were concentrated only in the intestine of the terminal fetus, probably because of an increased intake of PCB-containing amniotic fluid. The affinity of the PCBs, especially of the 2,4',5 trichlorobiphenyl, to lipids, and the increasing lipid content of the fetal tissue may offer an additional explantation of the increase in activity concentration during the fetal development.