The Enantioselective Bioaccumulation of Chiral Chlordane and α-HCH Contaminants in the Polar Bear Food Chain

Abstract

The enantiomer ratios (ERs) of R-HCH and chlordane related compounds (CHLs) were examined in the polar bear food chain (arctic cod-ringed seal-polar bear), using chiral gas chromatography-mass spectrometry (GC-MS). The cod showed near-racemic mixtures (ER ) 1) for most of the compounds. In contrast, ERs in ringed seal and polar bear were frequently nonracemic (ER * 1), due to enantiomer-specific biotransformation. As (+)-R-HCH was transferred up the food chain, it became more abundant relative to (-)-R-HCH. For the CHLs, there was no uniform trend for the ER changes and the increasing trophic level. Apparent chiral biomagnification factors (BFs) were calculated and up to a 20-fold difference in the BF between enantiomers was found. Analysis of chiral BFs relative to CB-153 indicated that oxychlordane was formed by ringed seal and metabolized by polar bears. However, the ERs did not change significantly as a result of these biotransformations. Multivariate statistical methods revealed the clustering of sample categories and were used to investigate the relationships between the ERs, chemical residue concentrations, and biological data. ERs were important variables for the sample groupings and for the class separation of male/female seals and fat/ liver tissues. The variance in the cytochrome P450 CYP2B protein content of bear liver could be explained by the variances in chemical residue data. In this analysis the ERs were of secondary importance. The ERs of some highly recalcitrant CHLs in polar bear adipose showed linear relationships with the age of the bears.

Hexabromocyclododecane Challenges Scientists and Regulators

“…For example, (+/-) -HCH are the major stereoisomers in technical HCH, but -HCH is the most abundant diastereomer in biota (11). Furthermore, enantioselective processes must be involved because enantiomeric ratios of (-) and (+) -HCH differ in biological samples (9,11,12). These findings clearly indicate the differing environmental fates of individual HCH stereoisomers.…”

Enantioselectivity in environmental safety of current chiral insecticides

“…However, enantiomers are known to selectively interact with biological systems that are usually enantioselective and may behave as drastically different compounds. The role of enantioselectivity in environmental safety is poorly understood for pesticides, and the knowledge gap is reflected in that the great majority of chiral pesticides are used and regulated as if they were achiral, that is, single compounds.Studies on chiral pesticides started to appear in the early 1990s (4,(5)(6)(7)(8)(9)(10)(11)(12). Studies so far show that microbial degradation of chiral pesticides is commonly enantioselective.…”

“…Studies on chiral pesticides started to appear in the early 1990s (4,(5)(6)(7)(8)(9)(10)(11)(12). Studies so far show that microbial degradation of chiral pesticides is commonly enantioselective.…”

Chiral pesticides

“…43) Scientists reported an efficient practical and systematic optical resolution method for gem-dihalocyclopropanecarboxylic acid (C) using chiral 1,1Ј-binaphthol monomethyl ether (B) as the key auxiliary to obtain (G) and (H) (Scheme 2). 41) Moreover, this method was applied to the synthesis of chiral pesticides [carpropamid (23), fencyclate (24) and pyrethroid with three asymmetric centers (25) 41) ] (Fig. 6).…”

“…Studies on chiral pesticides started to appear in the early 1990s. [19][20][21][22][23][24][25][26][27][28] Companies have been deeply interested in selling synthetic chiral pesticides as single enantiomers in the past decade. The key reasons why single isomers are less common than they could be are probably limited access to chiral raw materials and economic synthetic routes.…”