ed methods for analyzing chlorine dioxide samples based on EPA and Standard Methods, and some states have approved DPD colorimetric testing kits as a method to meet compliance for monitoring chlorine dioxide.
The new regulations also focus on the reduction of disinfection byproducts, and public water supplies have responded by adopting alternative treatment techniques like using chloramines instead of chlorine to reduce the levels of disinfection byproducts. Some systems are also using alternatives such as ozone and chlorine dioxide as the primary disinfectant. Other systems have tried reducing the organic matter in their sources as a way to reduce the formation of disinfection byproducts. There is not one answer for solving the disinfection byproduct formation due to the fact that every system has water with a different quality and chemistry makeup.
Testing Large Systems
In 1996, the Information Collection Rule (ICR) went into effect and requires large systems serving populations of more than 100,000 and a more limited number of systems serving between 50,000 and 100,000 to collect data with regard to the disinfectants being used, occurrence of disinfection byproducts and treatment technologies being utilized.
There were about 300 public water supplies with 500 treatment plants that participated in the study, which collected data from July 1997 to December 1998. This rule was intended to help evaluate the need for changing current treatment practices as well as determined future regulation of disinfectants and disinfection byproducts. The information collected as a result of this rule was intended to help develop the regulations for Stage 1 DDBR, but the data was not complete when the rule was being developed. It did, however, play a role in the development Stage 2 DDBR.
While current EPA regulations require monitoring of 11 disinfection byproducts, more than 500 disinfection byproducts have been identified in various drinking water sources.
The World Health Organization has established guideline levels for 14 DBPs (see Table 2). While the ICR focused on the disinfection byproducts, which are currently regulated, the Nationwide Disinfection Byproduct Occurrence Study looked at about 50 other DBPs determined as having a higher potential for toxicity than the currently regulated DBP. Some of these include compounds such as MX (3-chloro-4-dichloromethyl-5-hydroxy-2(5H)-furanone), brominated forms of MX (BMXs), halonitromethanes, iodo-trihalomethanes, and brominated species of halomethanes, haloacetnitriles, haloketones and haloamides.
The results of this study were published in September 2002. The study was conducted by the scientists from the EPA’s National Exposure Research Lab, University of North Carolina (UNC) and the Metropolitan Water District of Southern California (MWDSC).
At the time of the study, no qualitative methods existed for most of the high-priority DBPs; therefore, UNC and MWDSC helped in developing methods for detection and quantitation. Unfortunately, no single method could detect all of the DBPs of concern, so several methods were employed.
At this point, no methods have been approved by the EPA for continued monitoring of these DBPs, but they are continuing to refine methods for future regulations. The results of the study indicated the presence of the high-priority DBPs in the waters that were sampled. Many included in the study were brominated DBPs or iodinated DBPs due to the presence of naturally occurring bromide and iodine in public water supply sources.
Toxicological studies seem to indicate that brominated DBPs are more toxic than chlorinated DBPs, and iodinated DBPs are more toxic than brominated. Significant data of the study found that treatment plants that used chloramination without prechlorination formed the highest levels of iodo-trihalomethanes, and the highest concentrations of dichloroacetaldehyde occurred at plants that utilized chloramine and ozone for disinfection.
Most importantly, the study indicates that while we are trying to use other treatment technologies to reduce the reg