Effect Of Free Chlorine And Chloramines On Lead Release In A Distribution System

To comply with disinfection by-product regulations, many utilities have chosen to use chloramines rather than chlorine for residual maintenance in drinking water distribution systems. However, the switch to chloramines may expose these systems to another health risk - increased concentrations of lead. This study investigated total lead release in the presence of free chlorine and chloramine residuals in drinking waters produced from ground, surface, desalinated, and blended water sources. For both desalinated and blended finished waters, more total lead was released in the presence of chloramines than in the presence of free chlorine. Little research has focused on the effect of oxidation-reduction potentials on metal release. This work verified theoretical predictions from extensive field data that showed the chloramine redox potential was lower that the free chlorine redox potential under equivalent pipe and distribution system environments; however, the released lead in the lower redox potential chloramine environment was higher than in the lower redox potential chlorine environment. The article relates redox potential to pH and the controlling solid lead phase for lead release and demonstrates that theoretical thermodynamic diagrams are practical tools for predicting release of lead (and perhaps other metals) in distribution systems. Utility managers who select chloramines for residual maintenance can use this information to help avoid potential problems of violating the lead action level