Accumulation of hexabromocyclododecane diastereomers and enantiomers in two microalgae, Spirulina subsalsa and Scenedesmus obliquus

• Microalgae (S. subsalsa and S. obliquus) accumulate HBCDs by hundreds of times.
• Diastereomer and enantiomer selectivity of HBCDs in the algae was observed.
• No isomerization was found in the two algae.
• New metabolites TBCDi and TriBCDie were found in S. subsalsa but not in S. obliquus.

Selective accumulation and bioisomerization of hexabromocyclododecane (HBCD) diastereomers and their enantiomers have been reported in several aquatic organisms; however, these processes have not been evaluated in algae. In the present study, the accumulation of three HBCD diastereomers (α-, β- and γ-HBCD) was studied using two microalgae, Spirulina subsalsa and Scenedesmus obliquus, in the plateau phase for seven days. The accumulation ability of S. obliquus was greater than that of S. subsalsa, with steady state BCF values in the range of 390–469 and 174–350, respectively. For the three diastereomers, the accumulation trend of α-HBCD>β-HBCD>γ-HBCD was observed in S. subsalsa, whereas the accumulation trend of β-HBCD>α-HBCD>γ-HBCD was observed in S. obliquus. Contrary to the process typically occurring in fish, the bioisomerization from β- or γ-HBCD to α-HBCD was not observed in algae. α-HBCD exhibited selective enrichment of (+)enantiomer in S. subsalsa and (−)enantiomer in S. obliquus. No significant enantioselectivity was observed for β- and γ-HBCD. New metabolites, tetrabromocyclododecadiene (TBCDi) and tribromocyclododecatriene (TriBCDie), were observed in S. subsalsa for the first time, but these were not observed in S. obliquus.