Seasonal dependence of the chiral composition of α-HCH in coastal deposition at the North Sea

The environmental pollutant α-HCH was analysed in seawater, air and bulk deposition samples from the North Sea. Enantioselective analyses of the sample extracts gave evidence of the change of the direction of net air–water gas transfer of the contaminant in dependence on the season. Due to warmer water surface temperatures during late summer to early autumn the equilibrium of α-HCH between air and water is dominated rather by volatilisation than deposition. The volatilisation of non-racemic α-HCH, as known to occur from seawater, changes the enantiomeric ratio in air, which is reflected in the observed ratio in rain that passes the air column.