Health Indicator Report of Community Water: Total Trihalomethanes (TTHM) Concentration - Disinfection Byproducts
Disinfection byproducts (DBP) are formed when disinfectants, such as chlorine are used in a water treatment to inactivate (or kill) pathogens (i.e., disease causing organisms) present in the source of water (i.e., lake, river, reservoir, or ground water aquifer). Different disinfectants produce different types and amounts of DBPs that may be harmful to human health. Therefore, the Environmental Protection Agency (EPA) developed requirements or regulations for water treatment that would both protect people from waterborne pathogens and related diseases and the potential harmful effects of DBPs. Most common DBPs are produced when chlorine reacts with natural organic matter (e.g., decaying vegetation) present in the source water. Water in which DBPs are present is a very complex mixture. Formation and presence of DBPs is dependent on a number of factors, including the chemical disinfectant used, water quality conditions such as the content and amount of organic matter, pH, temperature, disinfection method used, and duration of treatment (how long disinfectant is in contact with the water, which means that if a person lives on the very outer edge of the water distribution system, the person will have higher levels of DBPs in the water than someone right next to the water treatment facility). Other factors include the combination or sequential use of multiple disinfectants or oxidants. Furthermore, the composition of the DBP mixture may change seasonally. The highest levels of DBPs are expected to be formed in water derived from surface sources (such as rivers, lakes, or reservoirs) because ground water usually contains little organic matter. About 500 different chlorination byproducts have been identified, including trihalomethanes (THMs) and haloacetic acids (HAAs), which are the most prevalent byproducts and some of which are carcinogenic to experimental animals. However, none of the individual DBPs dominates the toxicity of this mixture and potential chemically-related toxicity or health effects are a function of exposure to the DBP mixture. Some people who drink water containing TTHMs in excess of EPA's standard and over many years may experience health problems of the liver, kidney, or central nervous system and increased risk of developing some cancers (such as bladder, rectal, and colon cancer), especially cancer of the urinary bladder (http://www.who.int/ipcs/publications/ehc/ehc_216/en/; http://monographs.iarc.fr/ENG/Monographs/vol84/) . Some THMs have also been shown to cause adverse reproductive and developmental effects in experimental animal studies (such as reduced sperm motility). Among a few human studies evaluating the association between exposure to DBPs and reproductive and developmental effects or adverse pregnancy/birth outcomes, some suggested an increased risk from exposure to DBPs while others have shown none. Although findings about adverse pregnancy outcomes have not been definitive, DBPs have been implicated in fetal loss and a variety of adverse birth outcomes, including growth retardation and birth defects (e.g., neural tube defects). Note that exposure to THMs in drinking water may also occur by inhalation or skin absorption, in addition to ingestion of contaminated drinking water.
NotesData Source: New Mexico Environment Department's Drinking Water Bureau, New Mexico Safe Drinking Water Information System (SDWIS). Measured TTHM concentrations in finished drinking water can be used to understand the distribution of potential trihalomethanes (THM) exposure level for populations served by community water supplies. Due to potential errors in estimating service population, the measures may overestimate or underestimate the number of potentially affected people. These measures allow for comparisons of potential THM exposure between the populations served by different water systems over time.
Data SourceNew Mexico Environment Department, Drinking Water Bureau
Data Interpretation IssuesMeasures do not account for the variability in sampling, number of sampling repeats, and variability within systems. THM levels vary seasonally and therefore, quarterly samples may not capture maximum levels and may not even adequately reflect short-term levels. Also, THM levels are variable spatially and temporary within a distribution system. THM concentrations increase with time after disinfection and therefore, with distance from the water treatment plant. Furthermore, THM sampling locations may change over time, which can make difficult comparisons of measurements from year to year. Better estimation of THM levels would require spatial and hydraulic modeling of distribution systems. Beginning October 1, 2013, Stage 2 DBPR became effective. Systems are required to evaluate their distribution system and identify the locations with high TTHM, referred to as the locational running annual average (LRAA). Trihalomethanes typically continue to form in the distribution system over time so the highest concentration of these are most often found at the outermost edges of a distribution system (furthest from the water treatment facility) where the oldest water is found, where sampling locations for TTHMs are most appropriately located (the Maximum Retention Time or MRT Site). Finally, concentrations in drinking water cannot be directly converted to exposure estimates, because water consumption varies by climate, level of physical activity, and between people. Due to potential errors in estimating service population, the measures may overestimate or underestimate the number of potentially affected people. The majority of sample analytical results (over 50%) for TTHMs between October 1, 2013 and December 31, 2014, are deemed invalid for compliance purposes.
DefinitionTotal trihalomethanes or TTHM concentrations (measured as the sum concentration of chloroform, bromodichloromethane, dibromochloromethane, and bromoform in micrograms of TTHMs per liter of water or mcg/L) in community drinking water systems (CWS) are combined with information about each CWS (such as service population) to generate the following measures shown in this report: 1) statewide TTHM concentration distribution in CWSs by mean and maximum over time, 2) annual distribution of mean and maximum TTHM concentration for persons served by CWS and 3) annual distribution of mean and maximum TTHM concentration by CWS. EPHT data queries -- https://nmtracking.org/dataportal/query/selection/water/WaterSelection.html -- provide detailed results by year for 1) mean TTHM concentration by CWS for a select year, 2) maximum TTHM concentration by CWS for a select year, 3) mean TTHM concentration and the number of CWS by year, 4) maximum TTHM concentration and the number of CWS by year, 5) mean TTHM concentration and the number of persons served by year, 6) maximum TTHM concentration and the number of persons served by year, 7) quarterly distribution of number of CWS by mean TTHM concentration or 8) quarterly distribution by number of people served by mean TTHM concentration. Additionally, users may query the number of persons served and the number of CWS in the state for a select year. A CWS is a public water system (PWS) that serves year-round residents of a community, subdivision, or mobile home park that has at least 15 service connections or an average of at least 25 residents. These CWSs are a subset of all New Mexico PWSs. To measure TTHM concentration in CWS, drinking water samples are usually taken at entry points to the distribution system or representative sampling points after water treatment has occurred.
NumeratorConcentration of TTHM.
Healthy People Objective: EH-4, Increase the proportion of persons served by community water systems who receive a supply of drinking water that meets the regulations of the Safe Drinking Water ActU.S. Target: 91 percent
Other ObjectivesCDC Environmental Public Health Tracking, Nationally Consistent Data and Measures (EPHT NCDM)
What Is Being Done?THMs levels in drinking water from most community water systems (CWS) are low; however, there is wide variation in the levels of THMs found in CWS supplies across New Mexico. Regulation of Total THMs (TTHMs) under the Safe Drinking Water Act began with the 1979 TTHM Rule, which set an interim drinking water standard or Maximum Contaminant Level (MCL) for TTHM, defined as the sum concentration of four THMs (i.e., chloroform, bromodichloromethane, dibromochloromethane, and bromoform), of 100 micrograms per liter (100 mcg/L) or 100 parts per billion (100 ppb) for CWS serving 10,000 or more people and using a disinfectant. On December 16, 1998, EPA published the Stage 1 Disinfectants/Disinfection Byproducts Rule (Stage 1 DBP), which reduced the MCL for TTHM to 80 mcg/L or 80 ppb and increased the scope of the rule to include all CWS that disinfect. The 1998 rule had phased compliance with a date of January 1, 2002 for public water systems (PWS) with 10,000 or more people with a surface water or ground water under direct influence of surface water source and a date of January 1, 2004 for all other affected PWS (i.e. small surface water and all ground water systems). In 2006, EPA published the Stage 2 Disinfectants/Disinfection Byproducts Rule (Stage 2 DBP), which did not change the TTHM MCL, but changed how compliance with the MCL is calculated. The 2006 Stage 2 DBP rule requires that PWSs evaluate their distribution systems for appropriate number of water samples and sampling locations. Also, the scope of this rule increased to cover consecutive systems that receive finished water from other systems. The first reporting deadline for compliance with the Stage 2 DBP rule was in 2006; however, it will take a number of years before the rule requires the new compliance calculations based on routine sampling for TTHM. Community systems' drinking water is routinely monitored and tested for TTHMs by CWS to comply with the 80 mcg/L EPA standard for TTHMs. (A CWS is a system that serves at least 15 connections or an average 25 residents year-round, including most cities and towns, apartment buildings, and mobile home parks with their own water supplies.) In NM, initial monitoring was required for TTHMs in 2001 for large surface water public water systems and in 2003, for small surface water and all ground water systems. Every year, CWS send to their customers a consumer confidence report (also called a water quality report) that lists any levels of TTHMs measured. EPA also requires all CWS to give their customers public notice when their water supply violates the TTHMs standard. This would include information about what is being done to correct the situation. Other actions may be required to prevent serious health risk to drinking water customers, such as providing alternative drinking water supplies. However, people who use their private wells water for drinking are solely responsible for disinfecting and testing the water for TTHMs (for information about chlorination of private wells water and laboratories certified to test drinking water and certified home treatment units visit: https://nmtracking.org/environment/water/PrivateWells.html).
Evidence-based PracticesEvery year, CWS send to their customers a consumer confidence report (also called a water quality report) that lists any levels of TTHM measured. EPA also requires all CWS to give their customers public notice when their water supply violates the TTHM standard. This would include information about what is being done to correct the situation. Other actions may be required to prevent serious health risk to drinking water customers, such as providing alternative drinking water supplies. However, people who use their private wells water for drinking are solely responsible for disinfecting and testing the water for TTHMs (for information about chlorination of private well water and laboratories certified to test drinking water and certified home treatment units visit: https://nmtracking.org/environment/water/private_wells/Testing.html).
Health Program InformationTTHM measures are developed from CWS water quality data stored in the New Mexico Safe Drinking Water Information System (SDWIS) database, which is managed by the New Mexico Environment Department's Drinking Water Bureau. In NM, initial monitoring was required for TTHMs in 2001 for large surface water public water systems and since December 2003, all CWS are required to monitor for TTHM; however, the frequency of monitoring varies depending on source water type (e.g., surface water or ground water). Routine, required monitoring schedules can range from quarterly to triennially. [Different sampling frequencies complicate comparisons between and among different CWSs. When allowed for a system, annual or triennial monitoring takes place during the month of warmest weather and may therefore, overestimate average THM levels.] CWS which have state-granted disinfection wavers generally have no TTHM sample results.
Page Content Updated On 04/17/2019, Published on 04/17/2019