The effects of ozone and chlorine, used for antifoulant treatment of cooling waters and disinfection of polluted waters, on the nonvolatile organic constituents in such waters are examined using the complimentary techniques of high-pressure liquid chromatography (HPLC) and bioscreening. HPLC is used to separate the nonvolatile organic constituents which are detected by UV absorbance or cerate oxidimetry. The bioscreening method used is a determination of bacterial mutagenic activity. To date, no significant mutagenic activity has been determined for constituents separated from ozonized effluents of waste-water treatment plants.