Sodium molybdate dihydrate does not exhibit developmental or reproductive toxicity in Sprague-Dawley rats maintained on a marginal copper diet

Groups of 24 weanling female Sprague-Dawley rats were administered molybdenum (Mo) as sodium molybdate dihydrate (SMD) in drinking water at target dose levels of 0, 20, or 40 mg Mo/kg bw/day and fed a semi-purified marginal copper (6.2 ppm Cu) AIN-93 G diet for 8 weeks prior to mating, through cohabitation and pregnancy until Gestation Day 21. The objective was to confirm the reproductive and developmental effects of SMD reported by Fungwe et al. (1990) at estimated doses as low as 1.5 mg Mo/kg bw/day in a similarly designed study with marginal Cu diet (6.3 ppm). There were no test material-related effects at 20 or 40 mg Mo/kg bw/day on mortality, clinical observations, body weight, body weight gain, food consumption, estrous cycling, reproductive performance, maternal macroscopic pathology, ovarian or uterine parameters, litter size, resorptions, fetal sex ratio, fetal weight, or external fetal malformations or variations. Water consumption was increased compared to controls at both dose levels during the pre-mating and gestation periods, with no apparent adverse impact. There was no evidence of copper depletion in serum at any dose level. In conclusion, the no-observed-adverse-effect levels (NOAELs) for systemic, maternal reproductive, and developmental toxicity in this marginal Cu diet study are 40 mg Mo/kg bw/day, consistent with the results of guideline developmental and reproductive toxicity studies of SMD. The results of Fungwe et al. were not replicated, even at higher dose levels of Mo, and their inconsistencies with guideline toxicity studies of Mo are not explained by the marginal dietary Cu level.