VOLATILIZATION OF SELENITE IN AQUEOUS-MEDIUM BY A PENICILLIUM SPECIES

The transformation and accumulation of the oxyanion selenite in soluti on by a Penicillium species was monitored over a 2 wk period. The fung us was cultured under aerobic and acidic conditions in 5 l bioreactors at 25 degrees C with initial sodium selenite concentrations of 1000 m u mol l(-1). At this concentration selenite appeared to exert little o r no toxic effect on the growth pattern of the fungus and almost ident ical maximum biomass yields of 6.0 g l(-1) were attained in the presen ce and absence of selenite. Over the time period selenium in the aqueo us phase decreased by similar to 49.8% whereas selenium accumulation b y the fungal biomass averaged 36.6% of the total selenium originally p resent in solution. The transformation of selenite into volatile selen ium compounds amounted to an average value of similar to 8.8%: 3.7% du ring the lag and rapid growth phases and 5.1% during the stationary an d decline phases indicating the volatilization process to be both grow th and non-growth associated. These values accounted for similar to 95 .6% of the selenium originally added to the culture media. Activated c harcoal traps were successfully used to retain the volatile selenium c ompounds which were determined to be organic in nature and likely to b e dimethylselenide. The reduction of selenite to amorphous elemental s elenium was observed only during the decline phase of growth as eviden ced by a characteristic red colour of the bioreactor contents. It was concluded that selenium transformation processes associated with the b iomass, i.e. reduction and accumulation/assimilation, were of greater significance than biomethylation under the conditions used.