Temporal Changes and Stereoisomeric Compositions of 1,2,5,6,9,10-Hexabromocyclododecane and 1,2-Dibromo-4-(1,2-dibromoethyl)cyclohexane in Marine Mammals from the South China Sea

Stereoisomeric compositions of 1,2,5,6,9,10-hexabromocyclododecane (HBCD) and 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH) were investigated in the blubber of two species of marine mammals, finless porpoises (Neophocaena phocaenoides) and Indo-Pacific humpback dolphins (Sousa chinensis), from the South China Sea between 2005 and 2015. The concentrations of Sigma HBCD in samples of porpoise (n = 59) and dolphin (n = 32) ranged from 97.2 to 6,260 ng/g lipid weight (1w) and from 447 to 45,800 ng/g lw, respectively, while those of Sigma TBECH were both roughly 2 orders of magnitude lower. A significant increasing trend of Sigma HBCD was found in dolphin blubber over the past decade. The diastereomeric profiles exhibited an absolute predominance of alpha-HBCD (mostly >90%), while the proportions of four TBECH diastereomers in the samples appeared similar. A preferential enrichment of the (-)-enantiomers of alpha-, beta-, and gamma-HBCD was found in most blubber samples. Interestingly, the body lengths of porpoises showed a significant negative correlation with the enantiomer fractions of alpha-HBCD. Significant racemic deviations were also observed for alpha-, gamma-, and delta-TBECH enantiomeric pairs. This is the first report of the presence of TBECH enantiomers in the environment. The estimated hazard quotient indicates that there is a potential risk to dolphins due to HBCD exposure.