What's in the Water?
The primary reason we measure the level of various disinfectants in water is to ensure complete disinfection in order to protect public health. Disinfectants are measured in potable water applications as well as in pools, spas and wastewater applications. Under the Safe Drinking Water Act (SDWA), public water supplies are required to monitor the levels of disinfectants and disinfection byproducts to ensure they do not exceed the standards.
Amendments to the SDWA in 1996 required the U.S. Environmental Protection Agency (EPA) to develop rules to balance the risks between microbial pathogens and disinfection byproducts (DBPs). The rule is intended to strengthen protection against microbial contaminants, especially Cryptosporidium, and at the same time reduce potential health risks of DBPs. Prior to the 1996 amendments, the only regulation in regards to disinfection was from 1979, and established maximum contaminant levels (MCLs) of 100 ppb for the trihalomethanes.
In December 1998, the Stage 1 Disinfectant and Disinfection Byproduct Rule (DDBR) came out as the first rule under the 1996 amendment to the SDWA. The Stage 1 DDBR established maximum residual disinfectant level goals (MRDLGs) and maximum residual disinfectant levels (MRDLs) for three commonly used chemical disinfectants: chlorine, chloramine and chlorine dioxide. This rule also established MCL goals for the disinfection byproducts including: trihalomethanes, haloacetic acids, chlorite and bromate (Table 1).
In January 2006, Stage 2 DDBR was published, and strengthens public health protection for those being supplied water that is disinfected by requiring systems to meet the MCLs for trihalomethanes and haloacetic acids as an average at each sampling point instead of the system-wide average required in Stage 1. Depending on the size of the system and the amount of construction needed to comply, systems will begin the first year of compliance monitoring between 2012 and 2016 and must be within compliance with the Stage 2 DBP rule’s MCLs at the end of a full year of monitoring.
Samples & Sampling
Per the regulations, chlorine and chloramine monitoring requirements are the same in terms of number of samples and sampling point. They require as a minimum community water supplies and nontransient, noncommunity water supplies measure for residual chlorine and chloramines at the same point in the distribution system and at the same time as total coliform samples are collected.
Coliform sampling is based on the population served; therefore, the larger the population, the more disinfectant testing that needs to take place. Systems using chlorine as the residual disinfectant and operating booster chlorination systems must take three samples within the distribution systems. The samples should be collected as follows: one as close as possible to the first customer; one that is representative of the average residence time; and one as close as possible to the end of the distribution system.
In order to comply with the MDRL, systems running an annual average of monthly averages of all samples, computed quarterly, must be less than the established MDRL listed in Table 1. The EPA has approved several methods for measuring free and total chlorine based on ASTM and Standard Methods. Some states may have approved DPD colorimetric testing kits as a method to meet compliance of this rule.
Chlorine dioxide is mostly used to control taste and odor issues, but it is also used to oxidize iron and manganese and finally as a disinfectant and algaecide. Only systems using chlorine dioxide are required to monitor for this disinfectant.
Systems that are required to monitor must take daily samples at the entrance to the distribution system. Unlike chlorine and chloramines, the MDRL for chlorine dioxide cannot be exceeded for short periods of time due to potential health effects from short-term exposure to levels of the MCL of 0.8 mg/L. If any daily sample exceeds the MCL, the system is required to take three additional samples in the distribution system the following day.
The EPA has also approved 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 regulated DBPs, we are probably creating other DBPs that are not currently regulated but may be more toxic.
Testing & Disinfection
Disinfection of drinking water is critical to reducing illness and death due to microbiological pathogens that can occur in our water supply sources. The tradeoff is the potential formation of byproducts that can also present a health risk to the public. More studies need to be conducted on the toxicological effects of these emerging DBPs so we have a complete understanding of potential health effects.
In addition to studies that are looking at the ingestion of these DBPs by drinking the water, they are also beginning to look at other routes of exposure including inhalation and dermal absorption.