Biological interactions of selenocyanate: Bioprocessing, detection and toxicity

Abstract

The selenocyanate anion, SeCN⁻, has been reported in wastewater from refineries whose petroleum comes from Se‐rich marine shales. A metalloid‐resistant bacterium was exposed to aqueous solutions of SeCN⁻ to examine the relative toxicity of SeCN⁻, and the results were compared with the toxicity of selenate and selenite and another G16 metalloid oxyanion, tellurite. We also determined the volatile organo‐selenium species produced by bacterial cultures amended with selenocyanate anion, and we investigated a solid phase preconcentration technique for collecting SeCN⁻ from aqueous samples with different ionic strengths and subsequent detection using capillary electrophoresis. The relative toxicity of SeCN⁻ is comparable to that of selenate and selenite using the metalloid‐resistant bacterium LHVE as the test organism. Tellurite was more toxic at all concentrations examined than all three selenium‐containing anions, SeO₄ ²⁻, SeO₃ ²⁻, SeCN⁻. Live cultures of LHVE amended with 1 mM NaSeCN produced volatile organo‐sulphides and organo‐selenides that could be collected in headspace using a solid phase microextraction fibre. The bioprocessing, i.e. the reduction and methylation of SeCN⁻, is similar to that of selenate and selenite by other metalloid‐resistant bacteria. An aqueous 1.0 mM solution of SeCN⁻ could be captured from solution on solid‐phase extraction (SPE) cartridges using an aminopropyl‐based stationary phase. Selenocyanate anions, slowly pumped into a wetted SPE cartridge, were trapped on the cartridge’s solid phase and were subsequently eluted, thereby providing an increase in concentration above that of the original SeCN⁻‐containing solution. Preconcentration factors of 3.9 were achieved using a mixed sodium hydroxide/methanol elution solvent and by adding NaCl to aqueous SeCN⁻ before loading on the SPE cartridge.

Keywords:

• SeCN⁻
• environmental selenium
• petrochemical wastewater
• solid phase extraction of metalloid anions
• specific growth rate

Acknowledgements

The authors are indebted to the MECESUP Program, Chile, for allowing Mr. G.A. Pradenas to study at Dr. Chasteen’s laboratory. Claudio C. Vásquez received financial support from Fondecyt Grant #1060022 and Dicyt‐USACH, whilst Radhika Burra, James D. Fox and Thomas G. Chasteen received financial support from the Robert A. Welch Foundation (X‐011) at Sam Houston State University.