Reactions of dissolved organic matter (DOM) with photochemically-generated reactive halogen species (RHS) could be an important abiotic source of organohalogens in surface seawaters. To determine whether this is true it is necessary to overcome the analytical challenge of quantifying low dissolved organohalogen concentrations in the presence of high background halide ions. In this work, sequential solid phase extraction (SPE) and silver-form cation exchange filtration were utilized to desalt and pre-concentrate seawater DOM prior to non-specific organohalogen analysis by ICP-MS. Using this approach, native organobromine and organoiodine contents were found in the range 3.2-6.4 x 10-4 mol Br/mol C and 1.1-3.8 x 10-4 mol I/mol C (or 19-160 nmol Br L-1 and 6-36 nmol I L-1) within a wide variety of natural seawater samples, diminishing with ocean depth. We further demonstrate the formation in proportion to light fluence of organobromine and organoiodine at nanomolar levels during simulated and natural solar irradiation of DOM in artificial and natural seawaters. Increasing I- concentrations (up to 2.0 x 10-7 mol L-1) promoted increases of up to 460% in organoiodine content at the expense of organobromine formation under the same conditions. A chemical probe method using dimethyl-1H-pyrazole demonstrated the generation of RHS in these systems. The results suggest that sunlight-driven reactions of RHS with DOM may play a significant role in marine bromine and iodine cycling.

Sunlight-driven photochemical halogenation of dissolved organic matter in seawater: A natural abiotic source of organobromine and organoiodine

249th National Meeting (2015)

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