Acute molybdenum toxicity to rainbow trout and other fish

Molybdenum is generally reported in the literature to be acutely lethal to various fish species at relatively high concentrations (70 to >2000 mg/L). The toxicity of molybdenum to fertilized rainbow trout eggs and alevins (EA), however, is controversial as different bioassays demonstrate a wide toxicity range (0.73 to >90 mg/L Mo). A duplication of a previous study using similar water chemistry along with the standard bioassay protocol demonstrated that molybdenum was not acutely toxic to the early life stages of rainbow trout over 32 d up to a maximum molybdenum concentration of 400 mg/L. An additional bioassay exposing early life stages of rainbow trout to a maximum molybdenum concentration of 1500 mg/L for 32 d did not cause sufficient mortality to allow an LC50 to be calculated. Key words: molybdenum, toxicity, bioassays, rainbow trout.