Production and Release of Selenocyanate by Different Green Freshwater Algae in Environmental and Laboratory Samples

Abstract

In a previous study, selenocyanate was tentatively identified as a biotransformation product when green algae were exposed to environmentally relevant concentrations of selenate. In this follow-up study, we confirm conclusively the presence of selenocyanate in Chlorella vulgaris culture medium by electrospray mass spectrometry, based on selenium’s known isotopic pattern. We also demonstrate that the observed phenomenon extends to other green algae (Chlorella kesslerii and Scenedesmus obliquus) and at least one species of blue-green algae (Synechococcus leopoliensis). Further laboratory experiments show that selenocyanate production by algae is enhanced by addition of nitrate, which appears to serve as a source of cyanide produced in the algae. Ultimately, this biotransformation process was confirmed in field experiments where trace amounts of selenocyanate (0.215 ± 0.010 ppb) were observed in a eutrophic, selenium-impacted river with massive algal blooms, which consisted of filamentous green algae (Cladophora genus) and blue-green algae (Anabaena genus). Selenocyanate abundance was low despite elevated selenium concentrations, apparently due to suppression of selenate uptake by sulfate, and insufficient nitrogen concentrations. Finally, trace levels of several other unidentified selenium-containing compounds were observed in these river water samples; preliminary suggestions for their identities include thioselenate and small organic Se species.

Selective Gas Chromatography Mass Spectrometry Method for Ultratrace Detection of Selenocyanate

“…Starting from 10 to 25 ng/g Se­(VI), the algae promoted formation of SeCN – in the amount of 0.35–0.50 ng/g (Table ). This value is consistent with the concentration range reported in other studies using similar conditions …”

“…The hydrolysis of Et 3 OBF 4 releases H + (aq), turning the sample pH acidic. In these conditions, SeCN – is not stable and degrades to Se 0 . , For this reason, the samples were treated with NaHCO 3 before derivatization. The analytical response was monitored as a function of NaHCO 3 .…”

“…This value is consistent with the concentration range reported in other studies using similar conditions. 4 Wastewater and Matrix Interference. The determination of SeCN − is mostly performed for quality control of wastewater generated by gold mining, petroleum, and coal industries.…”

“…SeCN − is formed through the combination of elemental Se 0 and free cyanide (CN − ) and has been observed in various types of waters in concentrations that span a broad range. Trace levels of SeCN − (0.2 ppb or 1% of total dissolved Se) have been found in a Se-contaminated eutrophic river system, 4 and this species accounts for up to 10% of the Se in some flue gas desulfurization waters 5 and is the major form of Se in wastewaters from certain gold mining operations. 6 To comply with environmental regulations, industries must treat Se-containing wastewater before it can be released back into an aquatic system.…”

Selenomethionine: A Pink Trojan Redox Horse with Implications in Aging and Various Age-Related Diseases

“…Besides the rather prominent amino acid SeCys and intermediates involved in its biosynthesis from inorganic selenite SeO 3 2− and subsequent metabolic degradation to methylselenide CH 3 SeH, dimethylselenide (CH 3 ) 2 Se and dimethylselenonium (CH 3 ) 3 Se + , such natural small-molecule selenides are rare. The few notable exceptions found Nature include compounds such as the histidine derivative and ergothionine analog selenoneine present in tuna fish and inorganic selenocyanate (SeCN − ) in the green freshwater algae Chlorella vulgaris [4,5].…”