A method for reducing the effects of biological contamination in a hydrocarbon-containing system comprising the steps of continuously adding a formulation comprising tris(hydroxymethyl)phosphine or a tetrakis(hydroxymethyl)phosphonium salt to the system for one day or more； monitoring the efficacy of the continuous treatment by an assessment of the extent to which there is any effect on the environment that is attributable to metabolic activity of active microbes present in the system； wherein the tris(hydroxymethyl)phosphine or tetrakis(hydroxymethyl)phosphonium salt is added at a concentration of from 1 to 30 ppm based on the total volume of aqueous fluid added to the system, and wherein the formulation is added to the system at a stage to minimize incompatibility with any other chemicals that are added to the aqueous fluid. The treatment disrupts the microbial activity of active microbes in the hydrocarbon-containing system and can prevent or reduce detrimental effects arising from the presence of active microbes in the system.
