BIOCIDAL COMPOSITIONS

Embodiments of the present subject matter provide a biocidal composition comprising an aqueous mixture of (a) a phosphonium compound and (b) a polymeric ammonium compound， wherein the weight ratio of compound (a) to compound (b) is from 0.2:1 to 20:1， and wherein * the phosphonium compound (a) has formula: * wherein each R is independently a C 1-C6 alkyl group which is unsubstituted or substituted by a cyano， hydroxyl， esterified hydroxyl or aryl group; * R1 represents a C8-C18 alkyl group which is substituted or unsubstituted; and * X represents either chlorine or bromine; and wherein * the polymeric ammonium compound (b) comprises the repeat unit: * wherein each R 2 is independently a C1-C2 alkyl group which is substituted or unsubstituted; * R3 represents a C2-C18 alkyl or alkenyl group which is substituted or unsubstituted; and * R4 represents a C2-C18 alkyl or alkenyl group which is substituted or unsubstituted， a diethyl ether group， an isopropanol group， a N，N-dipropylurea group， or a 2-butene group.In some embodiments， the biocidal composition has a synergy index (SI) of less than 1 in relation to the effect of the composition on the inhibition of growth of biological organisms.