MILK TRANSFER AND NEONATAL UPTAKE OF COPLANAR POLYCHLORINATED BIPHENYL (PCB) CONGENERS IN MICE

The selective accumulation of 3,3',4,4'-tetrachlorobiphenyl metabolite s in late gestational foetal blood and soft tissues in mice as a resul t of administration of different coplanar polychlorinated biphenyl (PC B) congeners, is reported elsewhere. The situation in the nursing neon ate after maternal exposure to the same congeners is now studied: The C-14-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 co ngeners) and 2,3,3',4,4'-pentachlorobiphenyl (IUPAC number CB-105) (mo no-ortho congener) were injected intravenously in lactating mice at da y 11 post partum. One day and four days later, milk and neonatal/mater nal tissues and plasma radioactivity was monitored by liquid scintilla tion counting (dose: 2.0 mu mol (20-50 mu Ci)/kg body weight). In milk , CB-126, -169 and -105 showed higher levels (1450-2520 pmol/ml; one d ay after administration) than did CB-77 (580 pmol/ml), and in neonates , the relative whole-body levels of radioactivity (CB-169 and -105 hig hest) were related to the levels seen in milk (probably the consequenc es of their metabolic persistence). The comparably high C-14-concentra tion found in neonatal liver (about 15000 pmol/kg) after CB-126 admini stration and in plasma (880 pmol/ml) after CB-77 administration could be explained by binding to specific proteins. In general, neonatal mic e had two to seven times higher plasma levels than those of their moth ers. These results indicate that CB-126, -169 and -105 are transferred via milk to neonates in considerable quantity and are deposited mainl y in neonatal liver, whereas CB-77 is transferred in a comparably lowe r amount and accumulated in neonatal plasma. The lower C-14-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.