Variation of PCB congener levels during lactation period and relationship to their molecular structure

The levels of 22 polychlorinated biphenyl (PCB) congeners, including 13 coplanars (non-, mono-, and di-ortho-substituted chlorine) and 9 noncoplanar chirals (tri- and tetra-ortho-substituted chlorine), were measured in mothers milk from different mothers throughout their lactation periods. Important variations were found in the total PCB levels and PCB congener levels. The maximum PCB variations were found during the first weeks of lactation. Of the 22 PCBs analyzed, the most abundant, and those which had the highest variations were PCB-101, 118, 138, 151, 170, and 180, while the least abundant were the PCB-77, 126, 169, and 167, which also showed the lowest variation. Among the nonortho-substituted PCB congeners, PCB-77 was the predominant PCB in three of the four lactation periods studied, while PCB-126 was dominant in the last case. A relationship has been found between the levels and variations of total PCBs in the milk supplied by the different mothers and their dietary habits, weight changes and illness suffered during their pregnancy and lactation. The 22 PCB congeners investigated have been grouped in five categories according to their concentration variations in milk throughout the four different lactation periods. The PCB congeners included in each of the five groups have similar molecular structures. It has been found that coplanarity, number of chlorines and their molecular distribution, and neighbor H atoms were determinant factors in the process of PCB mobilization from the mothers' fats (where it had been able to accumulate throughout her life in the case of her first child) to the breast milk she delivered.