Biological formation of volatile phosphorus compounds

Phosphine and phosphides are reported to occur at numerous environmental si tes such as fresh and marine sediments, landfills, faecal matter, biogas di gesters and soils. The concentrations are several log units lower than the time-weighted average exposure standard, i.e. in the order of ng per m(3) o f gas or ng per kg material. Research about the biological formation of hig hly reduced gaseous phosphorus compounds dates back more than a hundred yea rs. The early reports had to deal with a lot of scepticism. Thanks to new a nalytical tools (gas chromatography) it has become clear, during the last d ecade, that phosphine is a global constituent of the atmosphere. Pure strai ns of micro-organisms cultivated under highly anaerobic conditions were sho wn to produce phosphine. Thermodynamic considerations indicate that it is v ery improbable that the reduction of phosphate to phosphine is endergonic. Therefore the generation of phosphine cannot be compared with sulphidogenes is and methanogenesis. There seems to be a link between the existence of hi ghly reactive gaseous phosphorus compounds and increased levels of metal co rrosion. The reactive compounds could be formed by micro-organisms or they are liberated from phosphorus-containing impurities in the iron by the acti on of bacterial metabolites. The biochemical pathways responsible for the p roduction of gaseous phosphorus compounds have not been characterised yet. (C) 2001 Elsevier Science Ltd. All rights reserved.