Chlorination by-products
Full Profile
| Group/Name | CAS No. | IARC Group | Monograph |
|---|---|---|---|
| Chlorinated drinking water | n/a | 3 | Volume 52 (1991) |
| Trihalomethanes (THMs) | |||
| Chloroform | 67-66-3 | 2B | Volume 73 (1999) |
| Bromodichloromethane (dichlorobromomethane) |
75-27-4 | 2B | Volume 52 (1991) Volume 71 (1999) |
| Dibromochloromethane | 124-48-1 | 3 | Volume 52 (1991) Volume 71 (1999) |
| Bromoform | 75-25-2 | 3 | Volume 52 (1991) Volume 71 (1999) |
| Haloacetic Acids (HAAs) | |||
| Monochloroacetic acid | 79-11-8 | n/a | -- |
| Dichloroacetic acid | 79-43-6 | 2B | Volume 84 (2004) |
| Trichloroacetic acid | 76-03-9 | 3 | Volume 84 (2004) |
| Monobromoacetic acid | 79-08-3 | n/a | -- |
| Dibromoacetic acid | 631-64-1 | n/a | -- |
| Haloacetonitriles (HANs) | |||
| Trichloroacetonitrile | 545-06-2 | 3 | Volume 52 (1991) Volume 71 (1999) |
| Dichloroacetonitrile | 3018-12-0 | 3 | Volume 52 (1991) Volume 71 (1999) |
| Bromochloroacetonitrile | 83463-62-1 | 3 | Volume 52 (1991) Volume 71 (1999) |
| Dibromoacetonitrile | 3252-43-5 | 3 | Volume 52 (1991) Volume 71 (1999) |
| Haloketones (HKs) | |||
| 1,1-dichloropropanone | 78-99-9 | n/a | -- |
| 1,1,1-trichloropropanone | 918-00-3 | n/a | -- |
| Others | |||
| Chloropicrin | 76-06-2 | n/a | -- |
| Chloral hydrate | 302-17-0 | 3 | Volume 84 (2004) |
| Cyanogen chloride | 506-77-4 | n/a | -- |
| 2,4,6-trichlorophenol | 88-06-2 | 2B | Volume 52 (1991) Volume 71 (1999) (as ‘polychlorophenols’) |
| MX | 77439-76-0 | 2B | Volume 84 (2004) |
| Chloramines | 10599-90-3 | 3 | Volume 84 (2004) |
| N-nitrosomethylethylamine | 10595-95-6 | 2B | Volume 17, Suppl. 7 (1987) |
General Information
Chlorination disinfection by-products (DBPs) are formed when chlorine-based chemicals are added to water to remove harmful microorganisms. Chlorine, chloramines, and chlorine dioxide are used most often and control microorganisms at the treatment facility and in the water distribution pipes.[8] Disinfection chemicals react with naturally present organic material in untreated water,[9] but most treatment facilities use system methods to reduce the amount of organic material prior to treatment with disinfectants.[8]
The formation of DBPs is complex and varies among different chemicals. For example, the formation of trihalomethanes (THMs) increases at high pH levels and decreases at low pH levels, while the opposite is true of haloacetic acids (HAAs).[9] Levels of THMs can increase as the water moves from the treatment plant through the distribution system, while mean concentrations of HAAs may decrease.[1] Other factors that influence levels of DBPs include water temperature, the amount of organic material present in the water (which tends to be higher in surface water than in ground water), chlorine dose, contact time, and bromide ion concentration.[9]
THMs and HAAs are the two major groups of disinfection byproducts in drinking water and are often found at the highest levels.[9] In general, chloroform is the most common THM,[9] while dichloroacetic acid and trichloroacetic acid are the most common HAAs.[10] A separate CAREX profile for Chloroform is available.
Early studies suggested an association between the consumption of chlorinated water and cancer of the bladder, the large intestine and rectum in humans.[9] However, the study designs were not optimal and did not differentiate between specific byproducts.[9] Subsequent studies conducted in the late 1990s suggest associations between DBPs and colon, rectal and brain cancer in humans, although the data "are not sufficiently reliable to confirm a dose-response or causal relationship,"[9] nor were specific DBPs targeted.
Studies of specific THMs show that chloroform can cause cancer of the kidney in mice and rats, malignant lymphomas in both male and female rats, and liver tumours in mice.[2] Ingestion of bromodichloromethane caused kidney and large intestine cancers in rats in some studies. Dibromochloromethane was not seen to cause cancer in rats; however there was some suggestion of carcinogenicity in female mice.[4] Bromoform has been associated with cancer of the large intestine in rats.[4] Ingestion of high levels of the HAA dichloroacetic acid has been associated with liver cancer in mice and rats.[5] Exposure to high levels of MX in drinking water has been associated with cancers at multiple sites in rats, including the liver, thyroid gland, adrenal gland, lung and pancreas in males, and in the liver, thyroid gland, adrenal gland and mammary gland in females.[5] Increased rates of lymphoma and leukemia were also observed in female rats given MX in drinking water.[5]
How did CAREX choose this agent for review?
Regulations and Guidelines
Chloroform has been evaluated and deemed not to be a toxic substance in Canada.[10] Inorganic chloramines were also evaluated by CEPA.[11] and were subsequently added to CEPA’s Toxic list under consideration for the environment and/or its diversity (not human health).[12] No other specific DBPs are identified as having been or as being under evaluation for toxicity under CEPA.
Health Canada has reviewed THMs and HAAs to support the formation of drinking water quality guidelines.
The World Health Organization reports that MX and chloral hydrate occur at concentration levels well below those at which toxic effects may occur and have not established guideline values for these DBPs.[11]
Drinking Water Quality Guidelines
| Canadian Guidelines[13] | Level (µg/L) |
|---|---|
| Trihalomethanes | MAC 100(a) |
| Canada Labour Code | MAC 16(a) |
| Haloacetic acids | 80(b) |
| US EPA Guidelines[14] | Level (µg/L) |
| Trihalomethanes | 80(c) |
| Haloacetic acids | 60(c) |
| World Health Organization[15] | Level (µg/L) |
| Trihalomethanes | Sum of the ratio of the concentration of each to its respective guideline should not exceed 1. |
| Chloroform | 300(d) |
| Bromodichloromethane | 60(d) |
| Dibromochloromethane | 100(d) |
| Bromoform | 100(d) |
| Dichloroacetonitrile | 20(d) |
| Dibromoacetritrile | 70(d) |
Environmental Exposures
Ingestion, inhalation and dermal absorption are all routes of exposure for the general public.
Canadians are exposed to DBPs by drinking treated water. People who drink treated water from above-ground reservoirs, lakes or streams with no pre-treatment filtration of organic matter may be exposed to higher than usual levels of DBPs.
Exposure may also occur by breathing air while bathing or showering, using chlorinated pools and hot tubs, or via dermal absorption during these activities. Inhalation is reported to be a more significant route of exposure for swimmers, while exposure via dermal absorption is more important in hot tub users due to higher water temperatures.[9]
A national survey of DBP levels in treatment plants and distribution systems was conducted by Health Canada in 1993;[16] selected results are show in the table below:
Disinfection By-Products in 53 Canadian Treatment Plants
and Distribution Systems, Summer 1993[16]
| Trihalomethanes | Measure | Range (µg/L) |
|---|---|---|
| Total* | Mean | 31.2 – 66.7 |
| Median | 17.2 – 90.9 | |
| Min. | 0.3 – 4.9 | |
| Max. | 74.9 – 342.4 | |
| Haloacetic acids | ||
| Dichloroacetic acids | Mean | 11.4 – 21.2 |
| Median | 10.4 – 22.6 | |
| Min. | 0.3 – 5.3 | |
| Max. | 23.8 – 163.3 | |
| Trichloroacetic acids | Mean | 21.4 – 48.9 |
| Median | 25.1 | |
| Min. | 0.04 – 2.1 | |
| Max. | 66.1 – 273.2 | |
| Others | ||
| Chloral hydrate | Mean | 3.6 – 8.4 |
| Median | 2.9 – 10.4 | |
| Min. | < 0.1 – 0.7 | |
| Max. | 20.1 |
More recent studies of HAAs in Canada reported similar levels of dichloroacetic acid and trichloroacetic acid, although maximum levels of 600 µg/L and 499 µg/L respectively were measured in Newfoundland.[10]
An analysis of 135 large (> 5,000 people served) and 312 small (< 5,000 people served) water treatment plants in Canada, using data from 1990 to 2004, found 12 percent of large systems and 44 percent of small systems had total HAAs above the guideline of 80 µg/L.[10
The Municipal Water and Wastewater survey is conducted yearly by Environment Canada.[17] Response is voluntary, so the data are somewhat incomplete. The 2004 survey does indicate that approximately 3 percent of Canadians have treated water without chlorine, 45 percent live in areas with at least one chlorinated system, and data are incomplete for the remaining 52 percent of the population.[18]
In 2009, Statistics Canada completed a survey of DBP levels in approximately 2,600 drinking water plants in Canada for the years 2005, 2006 and 2007. Levels of total HAAs, total THMs, and bromodichloromethane were reported by all surveyed facilities. Drinking water plants that serve fewer than 300 people were not included.[19]
Sources
- Nieuwenhuijsen, MJ. (2003). ‘Exposure Assessment in studies of chlorination disinfection by-products and birth outcomes’ Exposure Assessment in Occupational and Environmental Epidemiology (Ed. MK Nieuwenhuijsen) Oxford University Press.
- IARC monograph summary, Volume 73, 1999
- IARC monograph summary, Volume 52, 1991
- IARC monograph summary, Volume 71, 1999
- IARC monograph summary, Volume 84, 2004
- IARC monograph summary, Volume 17, Suppl. 7, 1987
- Wikimedia Commons Photo
- US EPA Safe Drinking Water Act, Drinking Water Treatment (2004)
- Health Canada 2006. Guidelines for Canadian Drinking Water Quality Guideline Technical Document Trihalomethanes
- Priority Substances List Assessment Report: Chloroform (2001) (PDF)
- Priority Substances List Assessment Report: Inorganic Chloramines (2001) (PDF)
- CEPA List of Toxic Substances (1999)
- Health Canada (2010) Guidelines for Canadian Drinking Water
- US EPA National Primary Drinking Water Regulations: Stage 2 Disinfectants and Disinfection Byproducts Rule
- World Health Organization, 2006. Guidelines for drinking-water quality, Vol. 1, 3rd edition incorporating 1st addendum.
- Health Canada, 1995. A National Survey of Chlorinated Disinfection By-Products in Canadian Drinking Water.
- Environment Canada, Municipal Water and Wastewater Survey
- CAREX Canada, 2009. Analysis of 2004 Municipal Water and Wastewater Survey by CAREX Canada staff.
- Statistics Canada, Survey of Drinking Water Plants (2005-2007)
Chlorination by-products are formed when chlorine-based chemicals are used to disinfect drinking water.
Environmental estimates are available for the following chlorination by-products:
Chlorination by-products are formed when chlorine-based chemicals are used to disinfect drinking water.
Environmental estimates are available for the following chlorination by-products:
Chlorination by-products are formed when chlorine-based chemicals are used to disinfect drinking water.
Environmental estimates are available for the following chlorination by-products:
Chlorination by-products are formed when chlorine-based chemicals are used to disinfect drinking water.
Environmental estimates are available for the following chlorination by-products:
Chlorination by-products are formed when chlorine-based chemicals are used to disinfect drinking water.
Environmental estimates are available for the following chlorination by-products:
Chlorination by-products are formed when chlorine-based chemicals are used to disinfect drinking water.
Environmental estimates are available for the following chlorination by-products:
Chlorination by-products are formed when chlorine-based chemicals are used to disinfect drinking water.
Environmental estimates are available for the following chlorination by-products:
Chlorination by-products are formed when chlorine-based chemicals are used to disinfect drinking water.
Environmental estimates are available for the following chlorination by-products: