The biodegradation of tributyl phosphate (Bu-3-P, TBP), releasing phosphate at a high enough concentration locally to precipitate uranium from solution, was demonstrated by a mixed culture consisting primarily of pseudomonads. The effect of various parameters on Bu-3-P biodegradation by growing cells is described. Growth at the expense of Bu-3-P as the carbon and phosphorus source occurred over a pH range from 6.5 to 8, and optimally at pH 7. Bu-3-P biodegradation was optimal at 30 degrees C, reduced at 20 degrees C and negligible at 4 degrees C and 37 degrees C. Incorporation of Cu or Cd inhibited, and Ni, Co and Mn reduced its degradation. Inorganic phosphate (above 10 mM) and kerosene (up to 1 g/l) reduced Bu-3-P biodegradation significantly, but nitrate had no effect. Sulphate (10-100 mM) was inhibitory. When pregrown biomass was used the fastest rates of tributyl and dibutyl phosphate biodegradation were 25 mu mol h(-1) mg protein(-1) and 37 mu mol h(-1) mg protein(-1) respectively. Microcarrier-immobilised biomass decontaminated uranium-bearing acid mine waste water by uranium phosphate precipitation at the expense of Bu-3-P hydrolysis in the presence of 35 mM SO42-. At 4 pH 4.5, 79% of the UO2+ was removed at a flow rate of 1.4 ml/h on a 7-ml test column.