Milk transfer and neonatal uptake of coplanar polychlorinated biphenyl (PCB) congeners in mice

The selective accumulation of 3,3',4,4'-tetrachlorobiphenyl metabolites in late gestational foetal blood and soft tissues in mice as a result of administration of different coplanar polychlorinated biphenyl (PCB) congeners, is reported elsewhere. The situation in the nursing neonate after maternal exposure to the same congeners is now studied: The 14C-labelled congeners 3,3',4,4'-tetrachlorobiphenyl (IUPAC number CB-77),3,3',4,4'5-pentachlorobiphenyl (IUPAC number CB-126), 3,3',4,4',5,5'-hexachlorobiphenyl (IUPAC number CB-169) (all three non-ortho congeners) and 2,3,3',4,4'-pentachlorobiphenyl (IUPAC number CB-105) (mono-ortho congener) were injected intravenously in lactating mice at day 11 post partum. One day and four days later, milk and neonatal/maternal tissues and plasma radioactivity was monitored by liquid scintillation counting (dose: 2.0 mumol (20-50 microCi)/kg body weight). In milk, CB-126, -169 and -105 showed higher levels (1450-2520 pmol/ml; one day after administration) than did CB-77 (580 pmol/ml), and in neonates, the relative whole-body levels of radioactivity (CB-169 and -105 highest) were related to the levels seen in milk (probably the consequences of their metabolic persistence). The comparably high 14C-concentration found in neonatal liver (about 15,000 pmol/kg) after CB-126 administration and in plasma (880 pmol/ml) after CB-77 administration could be explained by binding to specific proteins. In general, neonatal mice had two to seven times higher plasma levels than those of their mothers. These results indicate that CB-126, -169 and -105 are transferred via milk to neonates in considerable quantity and are deposited mainly in neonatal liver, whereas CB-77 is transferred in a comparably lower amount and accumulated in neonatal plasma. The lower 14C-levels in the NMRI mothers and offspring (about half of C57BL values in maternal and neonatal plasma), could possibly be explained by a differentiated metabolism of CB-77 in these two strains.