Seasonal variation in bone lead contribution to blood lead during pregnancy

Population blood lead level (PbB) often shows seasonal variation, frequentl y being higher in summer and lower in winter. As vitamin D metabolites also show seasonal variability, and the metabolites are associated with bone me tabolism, some authors have posited a role for bone lead release in seasona l PbB changes. We made third trimester and postdelivery PbB measurements on 414 immigrant women (98% Latina) in Los Angeles. We measured in vivo tibia and calcaneus (heel) lead concentration postdelivery via K-shell X-ray flu orescence. We saw evidence of seasonal variation in prenatal PbB, but not p ostnatal PbB. PbB was highest in spring and lowest in autumn. Tibia lead co ncentration was associated with prenatal PbB, as reported before. The contr ibution of tibia lead to prenatal PbB varied seasonally, with the greatest contribution occurring in the winter quarter and the least in the summer qu arter. The temporal pattern of bone lead contribution to PbB follows the se asonal alteration of insolation. There was no seasonal component in prenata l PbB associated with calcaneus lead, nor were there seasonal variations in either calcaneus or tibia lead contributions to postnatal PbB. Bone turnov er in the third trimester of pregnancy may be higher in winter months than in summer months, resulting in greater fetal lead exposure in spring than a t other times of the year. (C) 2001 Academic Press.