Biogenic brominated and iodinated organic compounds in ponds on the McMurdo Ice Shelf, Antarctica

During January 1994 seven meltwater ponds on the McMurdo Ice Shelf were investigated for their content of biogenic iodinated and brominated volatile hydrocarbons. An efficient purge and trap system in combination with a powerful gas chromatographic separation and an electron capture detector achieved detection limits of 0.02-0.4 ng l(-1), depending on the different substances. The following compounds could be identified and quantified: CH3I, CH2I2, CH2CII, CHBr3, CH2Br2, BrCH2CH2Br, CHBr2Cl, and CHBrCl2. This is the first time that 1,2-dibromoethane has been detected as a biogenic substance in the environment. In contrast to many other aquatic systems, where CH3I is found to be the most volatile iodine compound, CH2I2 showed the highest concentration in all ponds falling in the range of 5-20 ng l(-1). In three of seven ponds investigated, CH2CII was the second abundant iodinated substance. CHBr3 usually exhibited concentrations in the range of 2.5-8.6 ng l(-1). BrCH2CH2Br, previously not observed as a biogenic compound, was found to have concentrations similar to those of bromoform and even exceeded the bromoform content in two ponds and the CH2Br2 content in all ponds. Whether cyanobacteria, the dominant organisms in the ponds, are responsible for this distribution pattern must be clarified by further investigations.