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In order to elucidate the mechanism for diastereoisomer-specific toxicity and metabolism of hexabromocyclododecanes (HBCDs) in biota, zebrafish ( Danio rerio ) were exposed to different concentrations of individual HBCD diastereoisomers (α-, β- and γ-HBCD) in water for 7 and 21 d. We examined the gene expression of aryl hydrocarbon receptor (AHR) and cytochrome P450 (CYP), as well as ethoxyresorufin-O-deethylase (EROD) activity in zebrafish livers. Exposure to different HBCD diastereoisomers caused different expression of AHRs in zebrafish livers. For instance, 10 and 100 μg L −1 of α- and β-HBCD up-regulated the expressions of ahr1a and ahr1b in zebrafish liver, whereas 10 and 100 μg L − 1 of γ-HBCD down-regulated them after 7 d exposure. α-HBCD showed the most significant up-regulation of ahr1a and ahr1b expression, whereas γ-HBCD showed the most significant down-regulation of their expression among three HBCD diastereoisomers. Moreover, HBCDs could affect the expression of CYP1s as well as EROD activity in a gene-specific and diastereoisomer-specific manner. α-, β- and γ-HBCD inhibited cyp1a expression but enhanced the expression of cyp1b1 and cyp1c1. α-, β- and γ-HBCD showed different degrees of effect on the same CYP1 gene in a concentration-dependent way. The different effects of HBCD diastereoisomers on these genes we examined and EROD activity not only indicate diastereoisomer-specific toxic effect, but also in turn explain diastereoisomer-specific accumulation of HBCDs in zebrafish. [ABSTRACT FROM AUTHOR]

Abstract: Hexabromocyclododecanes (HBCDs) are now emerging ubiquitous contaminants due to their wide usage, persistence and toxicities. To investigate the bioaccumulative characteristics of HBCDs, sediments, Winkle (Littorina littorea), crucian carp (Carassius carassius) and loach (Misgurnus anguillicaudatus) were collected from two streams near an E-waste dismantling site in China, and HBCD exposure test was then conducted on Chinese rare minnow. The concentration of HBCDs was 14ngg−1 dry weight in sediments, 186, 377 and 1791ngg−1 lipid weight in winkle, crucian carp and loach, respectively. γ-HBCD was found to be the dominant diastereoisomer in the sediments (63% of total HBCDs). However, α-HBCD was selectively accumulated in the biotic samples and contributed to 77%, 63% and 63% of total HBCDs in winkle, crucian carp and loach, respectively. Moreover, an enrichment of (−)-enantiomers of α- and γ-HBCD were found in the winkle. The reverse results were observed in the crucian carp and loach. Similar observations of diastereoisomeric and enantiomeric composition were obtained in Chinese rare minnow with those found in the crucian carp and loach. These results indicate that the freshwater species from the streams are contaminated by HBCDs. α-HBCD can be selectively accumulated in organisms and the accumulative characteristics are enantioselective among species. [Copyright &y& Elsevier]