Developmental effects of boric acid in rats related to maternal blood boron concentrations

Timed-mated Sprague-Dawley rats (60/group) were exposed to boric acid (BA) from gestational days (gd) 0 to 20. BA added to the diet (0, 0.025, 0.050, 0.075, 0.1, or 0.2%) yielded boron (B) intakes of <0.35 (control), 3, 6, 10 , 13, or 25 mg B/kg body wt/d. Approximately one-half of the dams/group wer e terminated on gd 20, maternal whole blood collected and frozen, and prena tal outcome (fetal growth, viability, and morphology) evaluated. Remaining dams received control diet beginning on gd 20, and litters were monitored t hroughout lactation. Blood samples were prepared by a high-temperature alka line ashing method and analyzed for B by inductively coupled plasma (ICP) o ptical emission spectrometry. On gd 20, blood B concentrations of 1.27 +/- 0.298 and 1.53 +/- 0.546 mu g B/g were associated with the no-observed-adve rse-effect level (NOAEL) and lowest-observed-adverse-effect level (LOAEL) ( 10 and 13 mg B/kg/d, respectively) for developmental toxicity. Developmenta l toxicity persisted postnatally only at 25 mg B/kg/d, a dose associated wi th >10-fold increase in maternal blood B (2.82 +/- 0.987 vs. 0.229 +/- 0.14 3 mu g B/g for controls). Maternal blood B concentrations were: 1. Significantly elevated in all BA-exposed groups. 2. Positively correlated with maternal BA intake. 3. Inversely correlated with fetal body weight at doses above the NOAEL.