Investigation of source apportioning for alpha-HCH using enantioselective analysis.

Enantiomeric analysis can be used as a complementary tool for source apportionment of chiral compounds, particularly for alpha-HCH. In this study we used archived samples from studies related to the distribution of POPs in air-water and air-soil-grass systems. Such approach is based on the behaviour of chiral compounds released into the atmosphere from a primary source, when they are expected to show racemic or close to racemic composition. Contrarily, when chiral compounds have been reemitted from secondary sources (e.g. water or soil), their enantiomeric signatures are frequently non-racemic and are similar to the signature of the secondary source. To show such evidence, extracts from passive air samples deployed throughout Europe were analyzed for the enantiomers of alpha-HCH. The proximity to a large water body showed a high impact on the enantiomeric signatures: Baltic air had enantiomeric fractions (EFs) <0.500, while Mediterranean air had predominantly EFs >0.500. Similarly, Atlantic air showed a latitude influence: above 50 degrees N most EFs <0.500, whereas at latitudes below 50 degrees N, EFs were >0.500. A similar trend was also observed for EFs of alpha-HCH measured in air samples from a latitudinal transect during an Atlantic cruise. This transect shows that samples from higher latitudes (above 40 degrees N) have EF <0.500, whereas in the more southern samples (African coast and Southern Atlantic), there is no clear trend for EFs. Inland air samples showed a large range in EF values, with racemic signatures for samples with the highest alpha-HCH concentrations and an increasing spread in the EFs for lower alpha-HCH concentrations. As expected, the EF values of alpha-HCH in air, soils and grass were also impacted by latitude. Correlations between EFs and geographic characteristics of the sampling locations, as well as alpha-HCH concentrations, alpha-/gamma-isomer ratios, or temperature suggest that enantioselective analysis can give additional information on the distribution and sources of alpha-HCH in the environment.