RELATIONSHIPS OF LEAD IN BREAST-MILK TO LEAD IN BLOOD, URINE, AND DIET OF THE INFANT AND MOTHER

We have obtained stable lead isotope and lead concentration data from a longitudinal study of mobilization of lead from the maternal skeleto n during pregnancy and lactation and in which the newly born infants w ere monitored for 6 months postpartum to evaluate the effects of the l ocal environment on lead body burden of the infant. Samples of materna l and infant blood, urine, and diet and especially breast milk were me asured for 21 mothers and 24 infants. Blood lead concentrations were l ess than 5 mu g/dl in all except one subject. The mean lead concentrat ion in breast milk +/- standard deviation was 0.73 +/- 0.70 mu g/kg. I n seven subjects for whom serial breast milk sampling was possible, th e lead concentration varied by factors of from 2 to 4, and for three s ubjects there was an increase at or after 90 days postpartum. For the first 60-90 days postpartum, the contribution from breast milk to bloo d lead in the infants varied from 36 to 80%. Multiple linear regress;o n analyses indicated statistically significant relationships for some of the variables of isotope ratios and lead concentrations between bre ast milk, blood, urine, and diet for infants and mothers. For example, the analyses revealed that both a mother's breast milk Pb-207/Pb-206 and Pb-206/Pb-204 ratios and lead concentration provide information to predict her infant's blood Pb-207/Pb-206 and Pb-206/Pb-204 ratios. Th e major sources of lead in breast milk are from the maternal bone and diet. An evaluation of breast milk lead concentrations published over the last 15 years indicates that studies in which the ratio of lead co ncentrations in breast milk to lead concentrations in whole maternal b lood (x100) were greater than 15 should be viewed with caution because of potential contamination during sampling and/or laboratory analyses . Selected studies also appear to show a linear relationship between b reast milk and maternal whole blood, with the percentage of lead in br east milk compared with whole blood of <3% in subjects with blood lead levels ranging from 2 to 34 mu g/dl. The levels of lead in breast mil k are thus similar to those in plasma. Breast-fed infants are only at risk if the mother is exposed to high concentrations of contaminants e ither from endogenous sources such as the skeleton or exogenous source s.