Marine Bacterial Degradation of Brominated Methanes

Abstract

Brominated methanes are ozone-depleting compounds whose natural sources include marine algae such as kelp. Brominated methane degradation by bacteria was investigated to address whether bacterial processes might effect net emission of these compounds to the atmosphere. Bacteria in seawater collected from California kelp beds degraded CH_2Br_2 but not CHBr_3. Specific inhibitors showed that methanotrophs and nitrifiers did not significantly contribute to CH_2Br_2 removal. A seawater enrichment culture oxidized ^(14)CH_2Br_2 to ^(14)CO_2 as well as ^(14)CH_3Br to ^(14)CO_2. The rates of CH_2Br_2 degradation in laboratory experiments suggest that bacterial degradation of CH_2Br_2 in a kelp bed accounts for <1% of the CH_2Br_2 produced by the kelp. However, the half-life of CH_2Br_2 due to bacterial removal appears faster than hydrolysis and within an order of magnitude of volatilization to the atmosphere.