The potentiation of industrial biocide activity with Cu2+. II. Synergistic effects with 5-chloro-2-methyl-4-isothiazolin-3-one

The role of Cu²⁺ in enhancing 5-chloro-2-methyl-4-isothiazolin-3-one (IT) activity was investigated. This study was carried out in two directions. Firstly, the level of enhanced activity from a Cu²⁺ and IT mixture where environmental destruction of IT is minimal was examined. Secondly, the level of protection from Cu²⁺ in environments known to irreversibly reduce IT activity was studied. The bactericidal activities were determined in tryptic soy broth medium, mineral salt base-glucose medium and 0·9 NaCl solution. Under certain conditions, Cu²⁺ also stabilizes and/or protects the sensitive chlorinated IT molecule. Both synergistic activity and stabilization or protection by Cu²⁺ enhance the antimicrobial activity of IT under test conditions. Alternative sequential treatment with IT and Cu²⁺ was used to further characterize enhanced activity. The results suggest synergism. The utility of all the findings was investigated in metalworking fluid.