Part 2: Disinfection By-Products
The City of Craig clarifies myths about the upcoming switch to monochloramine in its water distribution system.
This edition of Straight Talk is intended to shine a light on the discussion of disinfection byproduct (DBP) production when using Chlorine vs. Monochloramine. We touched on DBP’s in our last edition of Straight Talk and in this update we will look at scientific data and information published about what DBP’s, how they are formed, and what we can expect from the use of monochloramine in our secondary disinfection process.
DBP Formation During Chlorination and Chloramination
By: GUANGHUI HUA & DAVID RECKHOW
Disinfection by-products (DBPs) have caused public health concerns since the discovery of chloroform as a chlorination by-product in drinking water in the early 1970s (Rook, 1974). Trihalomethanes (THMs) and haloacetic acids (HAAs) are the two most abundant classes of DBPs identified in waters treated with free chlorine. Some members of these two groups of DBPs are suspected human carcinogens (Singer, 1994). The Stage 2 Disinfectants/Disinfection Byproducts Rule sets the US maximum contaminant level for four THMs (chloroform, bromodichloromethane, dibromochloromethane and bromoform) and five HAAs (monochloro-, monobromo-, dichloro-, dibromo-, and trichloroacetic acids) at 80 ug/Land 60 ug/L, respectively, on the basis of a locational running annual average (USEPA, 2006).
A substantial number of halogenated DBPs other than THMs and HAAs have also been identified in chlorinated waters including haloacetonitriles, haloketone s (HKs), chloropicrin (CP), cyanogen halides (Krasner et al, 1989), and many others (Richardson, 2003). However, these DBPs are usually present in finished water at much lower concentrations than are THMs and HAAs. To date, the identifiable DBPs cumulatively account for no more than 50% of the total organic halogen (TOX) in most chlorinated drinking waters (Hua & Reckhow, 2007a; Zhang et al, 2000; Singer et al, 1995; Reckhow & Singer, 1984). Numerous halogenated DBPs formed from chlorine still remain unknown, and concern has arisen regarding the effect that these unknown DBPs might have on human health.
Drinking water utilities have been forced to evaluate their disinfection and treatment practices to meet increasingly stringent regulatory limits for DBPs. One strategy is to apply chloramines for maintenance of a residual in the distribution system. A survey conducted in 2004 found that 29% of the investigated water systems were using chloramines for secondary disinfection and another 3% were in the process of converting to chloramines (Seidel et al, 2005). In general, chloramination forms fewer THMs , HAAs, and TOX than does chlorination. Dihaloacetic acids (DHAAs) are the predominant known DBPs identified in chloraminated waters (Diehl et al, 2000). Researchers have found that a higher percentage of the TOX formed by chloramines cannot be accounted for by THMs and HAAs because known specific DBPs collectively account for only about 20% of the TOX concentration in chloraminated water (Hua & Reckhow, 2007a; Zhang et al, 2000).The slide below was presented at a scheduled Public Hearing at the Craig City Hall on January 8th. The DBP’s formed with regard to the use Free Chlorine and Monochloramine disinfectants is recapped below. The most prominent DBP formation that is specific to Chloramine and most written about is generally NDMA which will be addressed in more detail later in this discussion.
(Information Provided by the Water Research Foundation)
Since the early 2000s, many water utilities have moved away from chlorine disinfection to alternatives such as chloramine, chlorine dioxide, and ozone. Most of these utilities changed their method of disinfection to comply with U.S. Environmental Protection Agency (EPA) stan-dards for regulated disinfection by-products (DBPs), such as trihalomethanes and haloacetic acids.
Although these alternative disinfectants may reduce the formation of regulated DBPs, they often form other DBPs that are not currently regulated and may have adverse health effects. These DBPs include nitrogenous DBPs (N-DBPs) and iodinated DBPs (I-DBPs).
A nationwide assessment of nitrosamine occurrence found that approximately 1 in 10 samples in the data from the Second Unregulated Contaminant Monitoring Rule (UCMR2) contained N-nitroso dimethylamine (NDMA). The study found that NDMA formation is more signif¬icant in chloraminated water systems.
Iodinated DBPs I-DBPs are formed when iodine-containing water is disinfected with chlorine or chloramine. These I-DBPs are most often formed during chloramination and in situations when complete oxidation is prevented. They are found occasionally in waters originating from treatment plants located in coastal saltwater areas (Weinberg et al. 2002). I-DBPs often cause medicinal tastes and odors in drinking water and are being researched for possible adverse health effects. Preliminary research indicates I-DBPs are highly toxic to cells. One I-DBP, iodoacetic acid, is greater than 250 times more toxic to cells than the regulated DBP chloroacetic acid (Plewa and Wagner 2009).
Drinking water as a proportion of total human exposure to volatile N-nitrosamines.
Hrudey SE, Bull RJ, Cotruvo JA, Paoli G, Wilson M
Some volatile N-nitrosamines, primarily N-nitroso dimethylamine (NDMA), are recognized as products of drinking water treatment at ng/L levels and as known carcinogens. The U.S. EPA has identified the N-nitrosamines as contaminants being considered for regulation as a group under the Safe Drinking Water Act. Nitrosamines are common dietary components, and a major database (over 18,000 drinking water samples) has recently been created under the Unregulated Contaminant Monitoring Rule. A Monte Carlo modeling analysis in 2007 found that drinking water contributed less than 2.8% of ingested NDMA and less than 0.02% of total NDMA exposure when estimated endogenous formation was considered. Our analysis, based upon human blood concentrations, indicates that endogenous NDMA production is larger than expected. The blood-based estimates are within the range that would be calculated from estimates based on daily urinary NDMA excretion and an estimate based on methylated guanine in DNA of lymphocytes from human volunteers. Our analysis of ingested NDMA from food and water based on Monte Carlo modeling with more complete data input shows that drinking water contributes a mean proportion of the lifetime average daily NDMA dose ranging from between 0.0002% and 0.001% for surface water systems using free chlorine or between 0.001% and 0.01% for surface water systems using chloramines. The proportions of average daily dose are higher for infants (zero to six months) than other age cohorts, with the highest mean up to 0.09% (upper 95th percentile of 0.3%).
In our last update we discussed some of the known information related to monochloramines and many of the benefits related to its use and some of the precautions related to using this chemical compound as our secondary disinfectant.
Monochloramine, like free chlorine, is a disinfectant used to kill bacteria and other microbes as a part of drinking water treatment. While chlorine is the most commonly used primary disinfectant, an increasing number of water providers are using monochloramine to help them comply with new regulations. The new regulations are designed to limit certain disinfection byproducts in finished water. These disinfection byproducts – which are potentially harmful to humans -- are formed when organic and inorganic matter in the water react with chlorine or other disinfectants like monochloramine. As discussed above, the formation of regulated DBP production is generally substantially less than would be realized from chlorination.
Many water systems also favor the use of monochloramine because they experience fewer taste and odor complaints from customers than when using chlorination.
In this brief discussion of Straight Talk, as it relates to disinfection byproduct formation, exposure and regulatory control, we learned a few things about disinfection byproducts that can form when using chlorine and chloramination.
1. We learned that DBP’s can be formed from use of free chlorine and use of monochloramine as a secondary disinfectant.
2. We learned that DBP production from the use of chlorine is generally much higher given the right conditions than you would find from the use of monochloramine. (Especially THM and HAA production)
3. We learned that unique and unregulated DBP’s can be formed from the use of monochloramine under the right conditions.
4. We learned that using monochloramine as a secondary disinfectant is often deployed in order to combat DBP production and to ensure adequate residuals are maintained within the distribution system.
5. In our previous discussion, we talked about some of the precautions that kidney dialysis patients and pet-owners with aquariums would need to consider. These precautions are like the precautions taken when using chlorine as a disinfectant.
6. We learned that DBP formation is going to occur with the use of halogenated disinfectants like chlorine or monochloramine. Trained staff and management ensure that these chemical constituents are kept to a minimum in our distribution system.
7. We learned that with the use of monochloramine as our secondary disinfectant, we can expect lower concentrations of THMs and HAAs and with proper management of monochloramine, we can keep chemical constituents like NDMA to a minimum.
8. We also learned that NDMA in a Monte Carlo modeling analysis in 2007 found that drinking water contributed less than 2.8% of ingested NDMA and less than 0.02% of total NDMA exposure.
Overall we learned that monochloramine is the right solution for the City of Craig and provides the City with a solution that we can afford, which will be discussed further in future Straight Talk edition.
In our next edition of Straight Talk, we will discuss the alternative solutions to Craig’s chlorine residual compliance requirement that were considered and evaluated.
We hope that this information is useful as you consider what the change to monochloramine means for all of us. We all care about the quality of our water and the attractiveness of our community to others considering Craig as their home.
These changes to our disinfectant are important to each of us and developed in response to a State of Colorado CDPHE compliance order. The process of communicating this change has been a lengthy, and generally very public endeavor; however the City continues the educational process to help ensure that no one is left without understanding the impacts of switching to monochloramine.
Craig Water Department