Enantiomer‐specific biomagnification of α‐Hexachlorocyclohexane and selected chiral chlordane‐related compounds within an arctic marine food web

Abstract

Concentrations of achiral and chiral organochlorine contaminants (OCs), including hexachlorocyclohexane isomers (HCH), chlordane congeners (cis- and trans-chlordane, cis- and trans-nonachlor, MC5, MC7, and U82), and related metabolites (oxychlordane [OXY] and heptachlor exo-epoxide [HEPX]), were quantified in seawater (100 L; n = 6) and biota from the coastal Beaufort-Chukchi Seas food web near Barrow (AK, USA). The biota included zooplankton (Calanus spp.; n = 5), fish species such as arctic cod (Boreogadus saida; n = 10), arctic char (Salvelinus alpinus; n = 3), and marine mammals including bowhead whales (Balaena mysticetus; liver: n = 23; blubber: n = 40), beluga whales (Delphinapterus leucas; blubber: n = 20), ringed seals (Phoca hispida; blubber: n = 20), and bearded seals (Erignathus barbatus; blubber: n = 7). The food web magnification factors (FWMFs) for HCHs and chlordane compounds ranged from 0.5 (gamma-HCH) to 6.5 (HEPX) and were expected based on known recalcitrance and biotransformation of OCs. The enantiomer fractions (EFs) of all chiral OCs were near racemic (EF = 0.50) in the seawater, zooplankton, and all fish analyzed. In contrast, the EFs for most OCs analyzed were nonracemic (EF # 0.50) in the marine mammals blubber (range: 0.09-0.79) because of enantiomer-specific biotransformation and (or) accumulation. However, EF values were not significantly correlated with isotopically determined trophic level. The EFs for all chiral OCs (except alpha-HCH) in bowhead whale liver closely approximated the values in zooplankton, suggesting that the accumulation of chiral OCs from prey into this cetacean is not enantiomer specific. However, the modification of EFs from bowhead liver to blubber suggests that this species has the ability to enantioselectively biotransform and accumulate several chiral OC compounds.

Enantiomer Fractions of Organic Chlorinated Pesticides in Arctic Marine Ice Fauna, Zooplankton, and Benthos

“…The EFs of R-HCH in calanoid copepods in the present study (0.431) were lower than in the coastal Beaufort-Chukchi Seas (0.48) (9), but more similar to EFs from the Northwater Polynya (0.42) (10). Both Hoekstra et al (9) and Moisey et al (10) reported R-HCH EFs in zooplankton similar to those in water, suggesting nonenantioselective bioaccumulation. The EFs of R-HCH in pelagic T. libellula in the present study (0.409) were lower than EFs from the Northwater Polynya (EF ) 0.43, 10), which were both higher than in present T. libellula collected by bottom trawl (EF ) 0.348).…”

“…transChlordane and cis-chlordane were racemic also in European and North American arctic waters (1), and Arctic cod (Boreogadus saida) (9,14).…”

“…In the Canadian and Alaskan Arctic, marine zooplankton had (+)-R-HCH depletions similar to those of the water, suggesting no or limited biotransformation in these organisms (9,10). There are few data available on the enantiomer signatures of CPs in arctic marine invertebrates from other habitats, such as in association with sea ice (ice fauna) or the sea floor (benthos).…”

Chiral Chemicals as Tracers of Atmospheric Sources and Fate Processes in a World of Changing Climate

“…TC and CC were racemic in arctic-subarctic waters between 1994-2001. 26,40) The EF of CC averaged 0.497 in the North Atlantic-Greenland Sea in 2004, 41) while mean EFs of CC (0.516) and TC (0.469) were found south of Iceland in 2008. 42) Depletion of (+) TC was found in the Laurentian Great Lakes Superior, Erie and Ontario (mean EFs 0.474-0.478).…”

“…43) Enrichment of (+) HEPX was found in the central Arctic Ocean (mean EF 0.608), 26) the North Atlantic (mean EF 0.596) 42) and the Great Lakes (mean EFs 0.647-0.658), 43) while HEPX was racemic in the Beaufort Sea. 40) Climate warming is likely to impact algal and microbial communities in aquatic systems through loss of ice cover and consequent increased light intensity, earlier spring phytoplankton blooms, hydrological changes in wetlands which drain into rivers and lakes; and in the ocean, freshening due to lowered salinity.…”