Because the study participants' blood lead concentrations were relatively low -- most had values less than 5 micrograms lead per deciliter (100 milliliters) of blood -- the lead concentrations in their breast milk were also low - 0.7 parts per billion on average. These concentrations were not significantly different from those found in various kinds of infant formulae.
In spite of these low concentrations, the researchers found a strong correlation between the amount of lead in the mothers' milk samples and the corresponding blood lead levels of the infants. In fact, calculations based on the first 60 to 90 days postpartum indicated that 36 to 80 percent of the infants' total blood lead was coming from breast milk or formula.
"Our data indicate that lead from urban air and water where these infants reside contributed negligibly to blood lead, while soil and dust were not considered to be relevant sources because these infants had not reached the stage of crawling and ubiquitous hand-to-mouth activity," said Gulson. "Therefore, we concluded that dietary lead was the primary source contributing to the body burden observed in these subjects, with a major part of the dietary lead ultimately derived from the mothers' bones."
The researchers also found a statistical link between the lead concentration
in the maternal cord blood and lead levels in the first breast milk samples, a
finding that could have clinical significance. Bill Jameson, Ph.D., the
Institute toxicologist who serves as NIEHS project officer for the study, said
"If this relationship can be verified
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Contact: John Peterson
Peterso4@niehs.nih.gov
(919) 541-7860
NIH/National Institute of Environmental Health Sciences
3-Sep-1998