Biocidal compositions including a phosphonium quaternary surfactant compound and a biopenetrant, wherein the biopenetrant includes an anionic polymer of an anionic unsaturated carboxylic acid or a copolymer of an unsaturated carboxylic acid with a sulphonic acid, the polymer or copolymer being either terminated by vinylphosphonic acid (VPA) or vinylidene-1, 1-diphosphonic acid (VDPA) or having such monomers incorporated into the polymer backbone. The compositions preferably further include a quaternary ammonium salt cationic surfactant. The compositions optionally include a tetrakis(hydroxyalkyl)phosphonium salt biocide, wherein the salt is selected from sulphate, phosphite, bromide, fluoride, chloride, phosphate, carbonate, acetate, formate, citrate, borate, and silicate. Methods of using same are also provided.
