Volatilization of selenite in aqueous medium by a Penicillium species

The transformation and accumulation of the oxyanion selenite in solution by a penicillium species was monitored over a 2 wk period. The fungus was cultured under aerobic and acidic conditions in 5 1 bioreactors at 25 °c with initial sodium selenite concentrations of 1000 μmol l^-1. At this concentration selenite appeared to exert little or no toxic effect on the growth pattern of the fungus and almost identical maximum biomass yields of 6.0 g l^-1 were attained in the presence and absence of selenite. Over the time period selenium in the aqueous phase decreased by ~ 49.8% whereas selenium accumulation by the fungal biomass averaged 36.6% of the total selenium originally present in solution. The transformation of selenite into volatile selenium compounds amounted to an average value of ~ 8.8%: 3.7% during the lag and rapid growth phases and 5.1% during the stationary and decline phases indicating the volatilization process to be both growth and non-growth associated. These values accounted for ~ 95.6% of the selenium originally added to the culture media. Activated charcoal traps were successfully used to retain the volatile selenium compounds which were determined to be organic in nature and likely to be dimethylselenide. The reduction of selenite to amorphous elemental selenium was observed only during the decline phase of growth as evidenced by a characteristic red colour of the bioreactor contents. It was concluded that selenium transformation processes associated with the biomass, i.e. reduction and accumulation/assimilation, were of greater significance than biomethylation under the conditions used.