90-Day subchronic toxicity study of sodium molybdate dihydrate in rats

This study investigated the subchronic toxicity of molybdenum (Mo) in Sprague–Dawley rats given sodium molybdate dihydrate in the diet for 90 days at dose levels of 0, 5, 17 or 60 mg Mo/kg_bw/day. The study complied with OECD Test Guideline (TG) 408, with additional examination of estrus cycles and sperm count, motility, and morphology from OECD TG 416. The overall no-observed-adverse-effect level was 17 mg Mo/kg_bw/day, based on effects on body weight, body weight gain, food conversion efficiency and renal histopathology (females only) at 60 mg Mo/kg_bw/day. No treatment-related adverse effects on reproductive organ weights or histopathology, estrus cycles or sperm parameters were observed at any dose level. No adverse effects were observed in the high dose animals after the 60-day recovery period, with the exception that male rats did not fully recover from reduced body weight. Serum blood, liver and kidney samples were analyzed for molybdenum, copper, zinc, manganese, iron, cobalt and selenium; high levels of molybdenum and copper were found in the serum, blood, liver and kidneys of rats treated with 60 mg Mo/kg_bw/day. In conclusion, the LOAEL and NOAEL for molybdenum were determined to be 60 and 17 mg Mo/kg_bw/day, respectively.