Polysulfide sulfur in pipewall biofilms: its role in the formation of swampy odour in distribution systems

Biofilms and pipewall sediments in drinking water distribution systems were analysed for dimethylpolysulfides (DMPS) and inorganic polysulfides in an effort to determine the origin of dimethyltrisulfide, which causes unpleasant swampy odours in drinking water. Inorganic polysulfides were determined using the technique of methyl iodide derivatisation, and subsequent analysis as DMPS by gas chromatography-mass spectrometry. The technique was shown to be quantitative from 0.15 μg/L to 370 μg/L, and not subject to interference from other sulfur compounds. The polysulfide-rich biofilms and sediments occurred in pipes constructed from a variety of different materials, and fed by water from several different surface and groundwater sources. The biofilm/sediment matrix appeared to retard oxidation of polysulfides, by preventing their diffusion into the oxic water and by providing a barrier against the oxidative action of chlorine and dissolved oxygen.