Biannual cycles of organochlorine pesticide enantiomers in arctic air suggest changing sources and pathways

• Air samples collected during 1994–2000 at the Canadian arctic air monitoring stationAlert (82300 N, 62200 W) were analyzed by enantiospecific gas chromatography –mass spectrometry for -hexachlorocyclohexane (-HCH), trans-chlordane (TC) and5 cis-chlordane (CC). Results were expressed as enantiomer fractions (EF = quantitiesof (+)/[(+)+(−)] enantiomers), where EFs=0.5, < 0.5 and > 0.5 indicate racemic composition,and preferential depletion of (+) and (−) enantiomers, respectively. Long-termaverage EFs were close to racemic values for -HCH (0.504±0.004, n =197) andCC (0.505±0.004, n =162), and deviated farther from racemic for TC (0.470±0.013,10 n =165). Digital filtration analysis revealed biannual cycles of lower -HCH EFs insummer-fall and higher EFs in winter-spring. These cycles suggest volatilization ofpartially degraded -HCH with EF < 0.5 from open water and advection to Alert duringthe warm season, and background transport of -HCH with EF> 0.5 during the coldseason. The contribution of sea-volatilized -HCH was only 11% at Alert, vs. 32%15 at Resolute Bay (74.68 N, 94.90W) in 1999. EFs of TC also followed biannual cyclesof lower and higher values in the warm and cold seasons. These were in phasewith low and high cycles of the TC/CC ratio (expressed as FTC =TC/(TC+CC)), whichsuggests greater contribution of microbially “weathered” TC in summer-fall vs. winterspring.CC was closer to racemic than TC and displayed seasonal cycles only in 1997–20 1998. EF profiles are likely to change with rising contribution of secondary emissionsources, weathering of residues in the environment, and loss of ice cover in the Arctic.Enantiomer-specific analysis could provide added forensic capability to air monitoringprograms.

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NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

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