Aquatic acute toxicity assessments of molybdenum ( plus VI) to Daphnia magna

Generally, molybdenum (Mo) metals in the environment are very rare, but wastewater discharges from industrial processes may contain high concentrations of Mo, which has the potential to contaminate water or soil if not handled properly. In this study, the impact of three common compounds of hexavalent Mo (sodium molybdate (Na2MoO4 center dot 2H(2)O), ammonium molybdate ((NH4)(6)Mo7O24 center dot 4H(2)O) and molybdenum trioxide (MoO3)) in an aquatic system were assessed based on 48-h exposure acute toxicity to Daphnia magna (D. magna). The LC50 toxicities for associated conjugate ions including Na+, Cl-, SO42-, and NH4+ were determined. Furthermore, the LC50 values for the three forms of hexavalent Mo were determined, and the acute toxicities of the Mo forms were found to follow the order: (NH4)(6)Mo7O24 center dot 4H(2)O > MoO3 > Na2MoO4 center dot 2H(2)O in solution. (NH4)(6)Mo7O24 center dot 4H(2)O exhibited the lowest LC50 of 43.3 mg L-1 (corresponding to 23.5 mg Mo L-1) among the three molybdenum salts. The research confirmed that the toxicity of molybdenum in the aquatic system is highly dependent on the form of molybdenum salts used, and is also associated with the influence of the background water quality. (C) 2015 Published by Elsevier Ltd.