The environmental characteristics of industrial water treatment biocides are of great concern due to increasing regulatory pressure on water discharge and awareness of global ecology. A detailed knowledge of the environmental impact of a biocide is critical to its safe use and requires extensive testing. Isothiazolone biocides are broad spectrum antimicrobial which are used in a variety of industrial water treatment applications. In aquatic environments, these compounds rapidly biodegrade with half-lives significantly less than 24 hours. Metabolism involves cleavage of the isothiazolone ring and oxidation of the organic carbon to C02. Additionally, nucleophilic compounds may initiate degradation of these compound resulting in cleavage of the ring and the production of simple organic acids. Like most biocides, these compound show a significant degree of toxicity to non-target aquatic organisms; however, their rapid metabolism results in compounds which are 4-5 orders of magnitude lower in toxicity. Model systems studies have shown that typical use rates of isothiazolone biocides have no significant impact on biological waste treatment and do not generate halogenated byproducts. Thus, there is negligible environmental risk involved in the proper use of these biocides.
A wide variety of industrial biocides are used to control microbial growth and surface fouling in cooling water, paper mill, and oilfield systems. ? Effluent from cooling tower and paper mill systems is typically directed to a municipal biological wastewater facility for treatment prior to discharge to a receiving stream. In once-through cooling and oilfield applications the treated water is discharged directly to natural waters. Therefore, biocides used in all industrial water treatment processes are ultimately discharged to the environment.
A detailed knowledge of the environmental fate characteristics of industrial biocides is critical to their safe use and protection for the environment. A wide range of studies are required to filly understand the potential impact upon discharge.3 The key aspect to be considered is the risk assessment. Environmental risk can be simply defined as a function of a chemicals exposure and hazard. The hazard represents the toxicity to non-target organisms and exposure the concentration of a chemical in the environment. Thus a low risk and impact maybe obtained by use of low toxicity materials at high concentrations or higher toxicity materials used at low levels. In either case, a full data package is required to assess the potential impact of a biocide on the environment.
Isothiazolone biocides are currently used for microbial control in a wide range of industrial applications, including cooling water and paper. These biocides are effective at low concentrations, stable in use applications, fast-acting to inhibit growth and metabolism, and provide control over biofilm development.4?5?6 The initial studies on the fate and dissipation of isothiazolones in the environment were published by Krzeminski et al.7?8 Since this early work, regulatory requirements have changed and new methods and protocols have been specified for conducting environmental studies. In this paper, we describe the most recent information on environmental fate characteristics of methylchloro/ methylisothiazolone (MCMI)(l) and dichloronocty lisothiazolone (DCOI).(2) These studies include basic physical-chemical properties, biological and chemical degradation, and impact on waste treatment processes,
