Mechanism of disinfection: Incorporation of Cl-36 into f2 virus

The bacterial virus f2 was exposed for various periods of time to low concentrations of aqueous HOCl/OCl − labeled with radioactive HO 36 Cl/O 36Cl − (1 mg l −1 of free chlorine) buffered between pH 5.6 and 10.0. Aliquots of the reaction mixture were quenched with thiosulfate, the sample was assayed for viable f2, and the incorporation of 36Cl was measured. The virus sample was separated into its protein and RNA components by phenol extraction and the 36Cl activity was determined in each component. The rate of f2 inactivation by free chlorine paralleled the rate of 36Cl incorporation into the virus. Both rates were rapid at pH 5.6 and sluggish at pH 9.9. At pH 5.6, where f2 inactivation was most rapid, 87% of 36Cl bound to f2 was found in the RNA following exposure to the labeled hypochlorous acid. At pH 7.6 and 10.0, there was, respectively, 73 and 60% of bound 36Cl associated with the RNA. It appears that RNA has a greater affinity for chlorine between pH 5.6 and 9.9 than does protein. Associated with the slower inactivation of f2 at pH 7.6 and 9.9 was an increased amount of chlorine consumed through redox reactions. This would indicate that redox reaction rates do not parallel rates of virus inactivation.