Disinfection Byproducts Special Project

Project background

Disinfection of drinking water is one of the most important advancements protecting public health. Disinfection protects us from bacteria and viruses that may be present in untreated water. In order to ensure safe drinking water, most water supplies add disinfecting chemicals (chlorine and others) to the drinking water. When these chemicals react with possible pathogens or other parts of the drinking water, chemicals form that are called disinfection byproducts (DBPs). Exposure to DBPs can present some possible health risks, in addition to the clear benefits of reducing disease from pathogens.

Hundreds of different DBPs can occur in drinking water systems, both in treatment plants and across the distribution system. Many new studies on DBP occurrence and toxicity are published every year. While disinfection and DBPs have been present in drinking water for over one hundred years, we continually learn new information about DBPs. Some DBP nominations to the Contaminants of Emerging Concern (CEC) Initiative resulted from US Environmental Protection Agency (EPA) unregulated contaminant monitoring directing water utilities to sample for a number of possible contaminants, including DBPs (see The Fourth Unregulated Contaminant Monitoring Rule (UCMR4) (PDF)). The Minnesota Pollution Control agency has also nominated DBP chemicals due to their monitoring efforts in ambient surface water and groundwater.

The EPA has set limits for different groups of regulated DBPs, including trihalomethanes, haloacetic acids, chlorite, and bromate. Public water systems work very hard to maintain proper disinfection where required by EPA. Further information can be found on EPA’s website National Primary Drinking Water Regulations – Disinfection Byproducts. MDH also has additional information on DBPs and drinking water on the webpage Disinfection and Disinfection Byproducts.

While the benefits of disinfection are clear, quantifying these benefits is not possible within the standard risk assessment process used by the CEC Initiative. This is because our risk assessment process evaluates health risks and not health benefits.  Therefore, DBPs present distinct challenges when prioritizing them for review with other CECs.

Project details

Disinfection byproducts nominated to the CEC Initiative will be placed into this Disinfection Byproduct Special Project for evaluation. This separation from other nominated CECs is needed due to the beneficial aspects of disinfection, and to allow us to work closely with stakeholders to ensure that guidance values are developed for the most appropriate DBPs. Targeting any one particular DBP for reduction is a complex and difficult task where it is critical to maintain adequate disinfection. As some DBPs are considered carcinogens (along with other toxicities) when ingested for long periods of time, evaluating the health risks of DBPs is also a key role for public health agencies.

The CEC Initiative has both submitted its own nominations and received DBP nominations from stakeholders for full review. These nominations can be broken down into different chemical groups based on DBP type. The broad categories include haloacetic acids, trihalomethanes, and others. Specific information on each nomination can be found on our Nominated Contaminants Status and Information (PDF) document.

The nominations include:

Haloacetic acids (HAA)

• Monobromoacetic acid*
• Dibromoacetic acid*
• Tribromoacetic acid
• Monochloroacetic acid*
• Dichloroacetic acid*
• Trichloroacetic acid*
• Bromochloroacetic acid
• Bromodichloroacetic acid
• Dibromochloroacetic acid (also called Chlorodibromoacetic acid)
• Iodoacetic acid

*Regulated by EPA as a group under the HAA5 maximum contaminant level standard

Trihalomethanes (THM)

• Bromoform^†
• Dichloroiodomethane
• Iodoform

† Regulated by EPA as part of a group under the THM maximum contaminant level standard

Others

• Chlorate

All of the DBPs listed above were screened for toxicity and exposure information like other nominated CECs. However, numerous DBPs did not have sufficient toxicity information available to facilitate a full review. The nominated DBPs with insufficient data are:

• Monobromoacetic acid
• Dichloroiodomethane
• Iodoacetamide
• Iodoacetic acid
• Iodoform
• Tribromoacetic acid

Unregulated DBPs are a particularly interesting, but very challenging, area for the CEC Initiative due to the lack of toxicity testing data. The CEC Initiative will continue to monitor and incorporate the ongoing science surrounding DBPs, including the development of health-based guidance for DBPs where appropriate.

Project applications

The recommended uses of the results of the project are to:

• Provide a mechanism for the CEC Initiative to take into account the special circumstances of disinfection byproducts, and engage additional stakeholders prior to initiating a full review
• Bundle groups of related DBPs for review when necessary
• Develop a greater understanding of the public health impacts of decisions around health-based guidance development for the most important DBPs.
• Nominate important and understudied unregulated DBPs to federal agencies for further study
• Provide a bridge between special projects, such as leveraging insights gained from the Alternative Risk Assessment Special Project to evaluate DBPs

Funding for this special project is provided by the Clean Water Fund.