Mutagenic Activity Associated with Cooling Tower Waters Treated with a Biocide Containing 5-Chloro-2-methyl-4-isothiazolin-3-one

With the Ames Salmonella-mamMalian microsome test, significant mutagenic activity was detected in cooling tower water shortly (same day) after treatment with a biocide (CL2150) containing 5-chloro-2-methyl-4-isothiazolin-3-one (5-chloro-IT). Dose-related mutagenic responses with TA97 (-S9) and TA100 (-S9) were produced with the acid fraction (extracted at pH \u3c2 with methylene chloride) of this cooling water sample (specific mutagenic activities of 281000 and 118000 net revertants/L equiv of water, respectively). This mutagenic activity detected in cooling water sampled in mid-summer did not persist beyond the first day of CL2150 treatment. The mutagenic activity displayed by the cooling waters with TA97 (-S9) exceeded that associated with the extractable 5-chloro-IT concentration (determined by capillary gas chromatography-mass spectrometry)