Formation of cyanogen chloride from amino acids and its stability with free chlorine and chloramine.

Abstract

Cyanogen chloride (CNCl) is a disinfection by-product found in chlorinated and chloraminated drinking water. Although its chronic health effects are not well established, CNCl has been used as a chemical warfare agent and thus its presence in drinking water is of concern. CNCl is not currently regulated in the United States; however, it was on USEPA's 1991 Drinking Water Priority List and many facilities were required to report CNCl concentration under the Information Collection Rule. Uncertainty about the sources, formation mechanism, and stability of CNCl under water treatment conditions has been a factor limiting the establishment of regulatory standards. This research sought to improve our understanding of these issues. The findings of this research will help drinking water authorities to assess the necessity to regulate CNCl and determine the regulatory details, such as precursor, disinfection practice, temperature, and pH. The findings will also help water treatment utilities employ possible control strategies. Based on experimental results, this research has concluded: (1) amino acids are selectively important as CNCl precursor with glycine being the only important precursor; (2) CNCl formation from glycine agrees with a complex formation mechanism, in which glycine is completely converted to CNCl at pH 6--8 by pseudo first order kinetics; (3) once formed, CNCl decomposes with free chlorine through hypochlorite-catalyzed hydrolysis by second order kinetics with respect to hypochlorite and CNCl concentrations. CNCl, however, remains stable with chloramine. The different stability of CNCl with free chlorine and chloramine may, in part, explain the higher CNCl concentration observed in pre-chlorination post-chloramination systems than in chlorination systems; and (4) compared to many other amino acids, glycine is less reactive for chlorine, so when chlorine is not in excess such as drinking chlorinated water and during food preparation, most of glycine may not have the chance to react with chlorine and produce CNCl. The major difficulty in the study of CNCl formation and decay was that the traditional methods of CNCl analysis are not real-time measurements. A relatively new technique, in-line membrane introduction mass spectrometry (MIMS), was applied to overcome the analytical difficulty.