Purpose
The purpose of this investigation was to determine: (1) the mass balance of selenium or tellurium that was bioreduced when a selenium-resistant facultative anaerobe was amended with either selenium or tellurium; and (2) methods to analyze for these metalloids in biological samples.

Methods
Analytical methods were developed for the determination of selenium and tellurium in biological samples by hydride generation-atomic absorption (HGAAS). These methods were developed by:

(1) determining the optimal operating conditions for the determination of these metalloids by HGAAS;

(2) testing oxidation and reduction processes on known quantities of the metalloid;

(3) eliminating interferences in the determination of theses metalloids by HGAAS; and (4) applying these analytical methods to biological samples obtained from a culture of Pseudomonas fluorescens K27 amended with either selenite or tellurite.

Findings
1. The elimination of positive interference from the growth medium and the reagents used in the oxidation and reduction of these metalloids required dilutions before and after the oxidation by either nitric acid or hydrogen peroxide.

2. The chosen oxidant for selenium in the solid phase was nitric acid, and for the supernatant, it was hydrogen peroxide. The final reduction method used for selenium was 5 mL 12 N HCl and 5 mL of sample with 0.2 mL of 2% ammonium persulfate and heated in a boiling water bath for twenty minutes.

3. The chosen oxidant for tellurium in both the solid and supernatant was nitric acid. The final reduction method used for tellurium was 5 mL 12 N HCl and 5 mL of sample with 0.2 mL of 2% ammonium persulfate heated in a boiling water bath for twenty minutes.

4. When these methods were applied to bioreactor cultures amended with 10 mM selenite, 6.78% of the added selenite was reduced to biologically produced elemental selenium or Se species that had adhered to K27 bacterial cells.

5. In bioreactor cultures that were amended with 0.1 mM tellurite, 26.4% of the tellurite was reduced to elemental tellurium or Te species that had adhered to the cells.