Lead exposure among mothers and their newborns in Toronto.

Recent studies have suggested that a fetal blood lead level of 0.48 mumol/L (much lower than 1.21 mumol/L, which is the level previously believed to be toxic to the developing brain) may impair brain development permanently. We measured the maternal and umbilical cord blood levels of lead and free erythrocyte protoporphyrin (FEP) among 95 consecutive mother-infant pairs to determine whether neonates in Toronto are in the high-risk group. There was a significant correlation between the maternal and the cord blood lead levels (r = 0.59, p less than 0.0001). Most (99%) of the infants had cord blood lead levels below 0.34 mumol/L; in 11 cases the levels were below the detection limit of 0.01 mumol/L. The cord blood FEP levels were higher than the maternal levels. The US Centers for Disease Control, Atlanta, currently finds acceptable a blood FEP level of 0.62 mumol/L among children up to 10 years of age; however, this is not applicable to newborns since their higher FEP levels apparently reflect immature heme synthesis and increased erythrocyte volume rather than lead poisoning. Our data suggest that living in Toronto does not impose increased teratogenic risk from intrauterine exposure to lead; however, residents in high-risk areas should be followed up.