Environmental Fate and Ecotoxicology of Isothiazolone Biocides, 2000 Environmental Conference Proceedings

- T. M. Williams, A. H. Jacobson -- Understanding the fate and toxicity of industrial biocides in the environment is critical to their safe use. Isothiazolone biocides are broad spectrum antimicrobials which are used for microbial control in a variety of industrial water treatment and paper applications. In this study we evaluated the fate and ecotoxicology of chloromethylisothiazolone (CMI), methylisothiazolone (MI) and dichloro-n-octylisothiazolone (DCOI). Biological degradation studies using high performance liquid chromatography (HPLC) and radiotracer techniques showed that these compounds rapidly biodegrade in aquatic environments with half-lives significantly less than 24 hours. Metabolism involves cleavage of the isothiazolone ring and oxidation of the organic carbon to CO2. Degradation products were shown to be 4-5 orders of magnitude lower in toxicity than the parent molecules. Studies in model systems have shown no impact of isothiazolone addition on the efficiency of biological waste treatment. Toxicity tests using bioluminescence assays showed that isothiazolone degradation correlated with a decrease in the overall toxicity of the sample and a reduction in adsorbable organic halogen (AOX) content. These studies demonstrate that biodegradation of isothiazolone biocides is concentration dependent and results in ring-opened metabolites that do not contain organic-bound chlorine and are of low toxicity.