Enantiomer-Specific Transformation and Processing of Chiral POPs by Biota

2 Enantiomer-Specific Transformation and Processing of Chiral POPs by Biota 

Invertebrates had been thought to have poor capability to biotransform many POPs, as shown by experiment [186-188]. This lack is likely from low CYP abundance and activity. Chirahty has shown that while it is likely that most aquatic invertebrates do indeed lack the capacity to biotransform POPs, some species are capable of metabolizing some POPs stereoselectively. This finding is significant, as invertebrates are a major component of lower food webs, and bioaccumulation of nonracemic POPs results in more significant enantiomer-specific exposure and toxicity to predator organisms, including humans. 

Chirality has shown that at least some POPs are not likely to be biotransformed by some fish species. Some legacy POPs were racemic in fish, such as the toxaphene congener B7-1453 in cod liver oil [214], as well as cis- and ira 5 -chlordane, a-HCH, o,p -DDT, and photodieldrin in fish oils purchased from various countries [215]. Arctic cod Boreogadus saida) also had racemic amounts of a-HCH, cis- and ira 5-chlordane, U82, MC-5, and MC-7 [190, 216], as well as MC-6 [216] and PCBs [192]. Emerald rockcod (Trematomus bernacchii) in the Antarctic also had racemic residues of a-HCH [195]. 

The polycyclic musks HHCB and AHTN were present in significantly nonracemic amounts in fish in ponds filled by wastewater effluent discharge [235]. Rudd and carp had nonracemic levels of HHCB, while these species as well as tench and eel had nonracemic amounts of AHTN [235]. Pond water had racemic levels, suggesting some enantioselective biotransformation of the musks by these fish species. No correlation was observed between fish lipid levels and enantiomer composition. Cmcian carp has the most nonracemic amounts of tra 5-HHCB and trans-NIll [197]. Enantiomer compositions of musks were species-specific, most likely due to biotransformation, which may have been responsible for lower concentrations in carp compared to tench [197]. 

Pinnipeds (e.g., seals, walruses) are a key link in many marine food webs, in that they are commonly found, predate on fish, and are hunted in turn by sharks, polar bears, and Arctic Inuit peoples as part of their traditional diet. In these roles, pinnipeds play a significant role in bioaccumulating POPs and in transferring these contaminant burdens to higher trophic levels. Thus, an understanding of POP dynamics in pinnipeds is important in exposure and risk assessment, and an enantiomer-specific understanding is vital given that pinnipeds bioprocess POPs enantioselectively. 

---