Production of methyl bromide by terrestrial higher plants

Methyl bromide (CH3Br) is considered to play an important role in stratospheric ozone depletion, but its sources are currently not well defined. We have observed that Brassica plants can take up Br− from soil, produce CH3Br and release it into the air. Emission of CH3Br was detected from plants grown in natural soils containing 0.06–0.31 mg/kg Br−; the emission increases with increasing soil Br− level. We estimate that cabbage produces 0.4±0.2 Gg/yr, and rapeseed plants 6.6±1.8 Gg/yr. Given the ubiquitous distribution of Br− in soil, CH3Br production by terrestrial higher plants is likely a large source for atmospheric CH3Br.