Diastereomer- and enantiomer-selective accumulation and depuration of 1,2-dibromo-4-(1,2-dibromoethyl) cyclohexanes (DBE-DBCHs) and 1,2,5,6-tetrabromocyclooctanes (TBCOs) in earthworms (Eisenia fetida)

Due to the regulation of hexabromocyclododecane (HBCD), much attention has been paid to its potential substitutes, 1,2-dibromo-4-(1,2-dibromoethyl) cyclohexane (DBE-DBCH) and 1,2,5,6-tetrabromocyclooctane (TBCO). DBE-DBCH and TBCO contain several diastereomers and enantiomers, which may exhibit different environmental behaviors and biological effects. In this study, the accumulation and depuration of individual DBE-DBCH and TBCO diastereomers by earthworms (Eisenia fetida) from diastereomer-contaminated soils were evaluated. The accumulation and depuration kinetics of DBE-DBCH and TBCO diastereomers followed one-compartment first-order kinetics. The biota soil accumulation factor (BSAF) of beta-DBE-DBCH (2.74 g(oc) g(lip)(-1)) was 1.26 times that of alpha-DBE-DBCH (2.18 g(oc) g(lip)(-1)), while the BSAF of beta-TBCO (2.15 g(oc) g(lip)(-1)) was 1.62 times that of alpha-TBCO (1.3 g(oc) g(lip)(-1)), showing the diastereomer-specific accumulation of DBE-DBCH and TBCO. DBE-DBCH and TBCO diastereomers appeared to be transformed in earthworm-soil systems; however, no evidence of bioisomerization of the four diastereomers in earthworms was found, and no potential metabolites of debromination and hydroxylation were detected. Furthermore, the selective enrichment of E1-alpha-DBE-DBCH and E1-beta-DBE-DBCH (E1 represents the first enantiomer eluted) occurred in earthworms as the enantiomer fractions (EFs) for alpha-DBE-DBCH (0.562-0.763) and beta-DBE-DBCH (0.516-0.647) were significantly greater than those in the technical products (0.501 for alpha-DBE-DBCH and 0.497 for beta-DBE-DBCH, p < 0.05), especially in the depuration stage. The results demonstrated the diastereomer-and enantiomer-selective accumulation of DBE-DBCH and the diastereomer-selective accumulation of TBCO in the earthworm.

Automated summary

This study evaluated the accumulation and depuration of DBE-DBCH and TBCO diastereomers in earthworms and found that different diastereomers exhibited different accumulation and depuration kinetics.