GC determination of volatile organoiodine and organobromine compounds in Arctic seawater and air samples

Abstract

During September 1992 seawater and air samples were collected on Spitzbergen, Norway, and the concentrations of volatile organoiodine and organobromine compounds of biogenic origin were determined by a GC system supplied with a capillary column and an electron capture detector. A purge and trap technique was used to isolate the organohalogen compounds from the seawater samples, whereas the air samples were collected by an adsorption tube filled with Carbosieve S-III. The iodinated compounds CH3I, CH2I2, CH2C1I, CH3CH2CH2I and CH3CHICH3 were determined in Arctic seawater and air samples with mean concentrations in the range of (0.3–6.2) ng/l and (0.7–2) pptv, respectively. This is the first time that 1- and 2-propyl iodide could be analysed both in atmospheric samples and in seawater samples of the Arctic. CH2Br2, CHBr3, CH2BrCl, CHBrCl2 and CHBr2Cl were determined as biogenic brominated methanes in mean concentrations of (0.1–164) ng/l and (0.1–0.5) pptv in seawater and air samples, respectively. The highest concentrations in seawater samples were found for CH2I2 and CHBr3, respectively, whereas in air samples the most abundant iodinated compound was CH3I and the most abundant brominated compounds with equal mean concentrations were CH2Br2 and CHBr3. Significant differences were found in the seawater concentration from the middle of the fjord and the shore site, compared with samples from a field of algae. In all cases the concentration was higher for the samples from the field of algae with an especially high excess by a factor of 4–9 for CH2I2 and CHBr3. This result shows that algae are an important biological species in the polar region for the production of these halogenated substances. Whereas the brominated compounds in seawater samples correlate well with each other, CH3I or any other iodinated compound does not correlate with the bromomethanes. This indicates a different biogenic mechanism for their formation. Under certain preconditions the annual flux from the Arctic Ocean to the atmosphere could be calculated for CH3I to be 4×109 g, for CHBr3 to be 5.4×1010 g, which is an essential contribution to the total global budget of these important atmospheric trace gases.