PRODUCTION OF VOLATILE ORGANOHALOGENS BY PHYTOPLANKTON CULTURES

Natural volatile halocarbons are important as carriers of reactive hal ogens to the troposphere and, in the case of the more stable compounds , to the stratosphere. Bromoform (CHBr3) has been of particular intere st as a potential source of bromine which might account for sudden ozo ne depletion events in the Arctic boundary layer. The oceans have been shown to be major contributors of volatile halocarbons to the atmosph ere, but the sources of halocarbons within them have been unknown exce pt for macrophytic algae which are normally confined to the coastal zo ne. Here we report experiments that demonstrate that certain unialgal cultures of marme phytoplankton produce a suite of halocarbons (CHBr3, CHBr2Cl, CH2Br2). The production rate of each of these halocarbons is dependent on both species and growth stage. Chloroiodomethane which a lso appeared in the cultures could be attributable to photochemical pr oduction from a precursor (CH2I2). Great caution should be shown in ex trapolating the rates estimated from these controlled experiments to t he marine environment.