Environmental biotransformation of chiral polychlorinated biphenyls and their metabolites

• Main Author: Lv, Zhe
• Other Authors: Wong, Charles S. (Chemistry), Wang, Feiyue (Chemistry) McKenna, Sean (Chemistry) Farenhorst, Annemieke (Soil Science) Wania, Frank (Physical and Environmental Sciences,University of Toronto Scarborough)
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: ACS Publications 2013
• Subjects: Chiral polychlorinated biphenyls; Biotransformation; Cytochrome P-450 isozymes; Nanoparticles; Greenland shark; Arctic food web; Metabolites; Bioaccumulation; Arctic; Canada; Cumberland Sound; Greenland; Norway; Svalbard; Beluga; Beluga*; Harp Seal; narwhal*
• Online Access: http://hdl.handle.net/1993/22286

This dissertation combines laboratory and field experiments to investigate the mechanisms of atropisomer enrichment for chiral polychlorinated biphenyls (PCBs) and their metabolites in organisms. Stereoselective biotransformation and bioaccumulation were identified as two major reasons for the different environmental fate of PCB atropisomers. Other affecting factors, such as presence of nanoparticles and changes in feeding ecology of organisms, also affect the fate of chiral contaminants. In vitro incubations of rat cytochrome P-450 2B1 (CYP2B1) isozyme with chiral PCBs indicated that different biotransformation kinetics and competition among PCB congeners or between atropisomers were two main factors affecting atropisomer enrichment. Different interactions between chiral PCB congeners or atropisomers with rat CYP2B1 may occur at the molecular level. Non-racemic meta-hydroxylated-PCBs (5-OH-PCBs) were the major metabolites. CYP-mediated stereoselective formation of dihydroxylated PCBs from OH-PCBs was observed. Gold nanoparticles affected biotransformation activity of rat CYP2B1 and changed PCB atropisomeric composition, directly by electrostatic interaction, or indirectly by changes to the surrounding ionic strength. Thus, stereoselective metabolism of chiral PCBs and OH-PCBs by CYPs is a major mechanism for atropisomer enrichment of PCBs and their metabolites in the environment, with the degree of enrichment dependent, at least in part, on charged nanoparticles and stereoselective interference of atropisomers with each other at the enzyme level. The atropisomer compositions of chiral PCBs were measured in the marine biota of Cumberland Sound (Canada) and Svalbard (Norway). High trophic level organisms, including harp seal, beluga, and narwhal reported for the first time, had species-specific atropisomer signatures, likely due to a combination of in vivo biotransformation and trophic transfer. PCB chiral signatures in Greenland sharks supported the hypothesis that some of these PCB atropisomer compositions ...