Toxicity of oxyanions of selenium and of a proposed bioremediation intermediate, dimethyl selenone

The relative toxicity of selenate, selenite, and dimethyl selenone were assessed by determining growth inhibition and growth rate inhibition of Pseudomonas fluorescens K27 and using the Microtox® bioassay method at varying concentrations of these three selenium species. The results of EC50 vary depending on the organism tested and the method used; for P. fluorescens K27, EC50 increased in the order of dimethyl selenone < selenate < selenite. However, for Vibrio fisheri, EC50 increased in the order of selenite < dimethyl selenone < selenate. The possibility that different reduction mechanisms may dominate the remediation of the two selenium oxyanions with different oxidation states by P. fluorescens K27 is discussed, as is whether dimethyl selenone is a possible intermediate in selenium reduction and methylation.