Biomethylation of metals and metalloids of Group 14 and 15 metals such as tin, lead and arsenic takes place in the environment, but information about methylated bismuth compds. is rather limited, although bismuth compds. are used widely in alloys, cosmetics and pharmaceutical products. Cryotrapping gas chromatog. and hydride generation gas chromatog. coupled with an ICP-MS as a bismuth-selective detector were used to det. volatile bismuth compds. in landfill and in sewage gas, as well as non-volatile methylated compds. in water and sediment samples. One volatile bismuth compd. could be detd. in gaseous samples; it was identified as Me3Bi (TMB) by element-specific detection (ICP-MS, m/z 209), matching the retention time with a TMB std. The mol. structure was recently confirmed by gas-chromatog. fractionation with MS-ion trap detection (electron impact). Among other volatile metal compds., TMB is a major component in the gases of sewage sludge digesters: concns. of up to 25 mg m-3 have been measured at eight sewage treatment plants. The concn. in landfill gas was approx. one order of magnitude lower. In lab. expts., fermentors contg. an anaerobic culture from a clean pond sludge were mixed with contaminated soil from four different industrial areas. After an incubation time of two weeks at 30 Deg in the dark, TMB was detected in the headspace of all the samples. The volatilization rate of bismuth did not correlate with the total amt. of bismuth in the sediments or with the available fraction after acid digestion following hydride generation. Some evidence was obtained for the occurrence of methylated bismuth compds. in water samples and in sediments.