Trihalomethanes (THM) in drinking water

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THMs are trihalomethanes, chemical compounds that can be formed when water is disinfected with chlorine. THMs occur when chlorine reacts with organic matter, naturally present in water, such as decaying leaves, and for this reason THMs are common in surface water supplies (lake & rivers) throughout Canada. Saint John’s water comes from surface supplies. The north, south and east parts of Saint John receive water from Latimer Lake and the Loch Lomond watershed. The west side of Saint John generally receives its water from the Spruce Lake watershed which is supplemented at times by the Musquash watershed.

The chemical reaction between chlorine and organic matter forms a group of chemicals known as disinfection by-products. The most common of these by-products are trihalomethanes (THMs). THMs include four chemical compounds: bromodichloromethane (BDCM), dibromochloromethane (DBCM), chloroform and bromoform.

The acceptable level, or guideline, for THMs in drinking water in Canada is set by Health Canada in consultation with the provinces and territories. The Canadian drinking water guideline for total THMs is 100 micrograms of THMs per litre of water (µg/L). The guideline is based on a locational running annual average of a minimum of four quarterly samples [an average of the samples from the same place]. The updated guidelines for total THMs were released by Health Canada in April 2009. For more information, go to Guidelines for Canadian Drinking Water Quality: Technical Document: Trihalomethanes – 2009 Health Canada Addendum (http://www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/trihalomethanes/addendum-eng.php).

 

There is concern among experts in Canada that THMs, may pose a risk in the development of cancer. Some studies report an association between elevated THMs and reproductive effects, though there is presently insufficient evidence to establish a specific relationship, suggesting the need for more studies.

The guidelines represent a level of exposure that is deemed acceptable by Health Canada for a typical life span (70 years) and that will not cause an increased risk to health. It takes into account all three methods of exposure: ingestion, inhalation and skin absorption.

 

Canadians can be exposed to THMs when drinking tap water containing the chemical compounds. Showering, bathing and other water use activities can also contribute to an individual's total exposure. For example, THMs can evaporate from the tap and be inhaled during showering, or they can be absorbed through the skin during bathing. These types of exposure have been considered in the guideline setting process. Water that meets the total THMs guidelines is considered safe for all domestic uses, including drinking, bathing, showering and food preparation.

 

To reduce or eliminate THMs in drinking water use a water pitcher with an activated carbon filter, install a tap-mounted carbon filter, or to use bottled water. When using a filter, check to verify that it is certified to NSF Standards for removal of THMs and follow replacement instructions recommended by the manufacturer. Such devices if not properly maintained can become sources of bacterial contamination in water. When using bottled water, check to verify that the supplier is a member of the Canadian Bottled Water Association or the International Bottled Water Association. Individuals may also want to keep the length of time spent in showers or baths to a minimum in areas with elevated levels of THMs in drinking water.

 

Most private well water supplies are not disinfected. The lack of chlorine disinfection means there should be no THMs present.

 

Without adequate disinfection of our water supplies, the health risks from micro-organisms would far outweigh the risks from THMs. Drinking water is disinfected with chlorine to kill bacteria and viruses that can cause serious illnesses and deaths. In fact, chlorination of drinking water has virtually eliminated typhoid fever, cholera and many other diseases; it represents one of the greatest achievements of public health protection.

Secondly, drinking water disinfection is necessary because once the treated water leaves the treatment plant, it may travel through water mains and pipes sometimes at significant distances, before it reaches its destination. During this time, it is necessary to maintain a chlorine residual level of disinfectant in the water to ensure no possible regrowth of micro-organisms. Without adequate disinfection, the health risks from microorganisms far outweigh the risks from THMs.

 

Levels normally vary within a single water supply depending on the season, water temperature, amount of natural organic matter in the water, pH, amount of chlorine used, time the water is in the distribution system and other factors.

The concentration of chloroform – one of the four THM chemical compounds is approximately two to three times higher during summer months as during winter months.

 

The City of Saint John is working in conjunction with the New Brunswick Departments of Health to monitor the level of THMs so that they are within the guideline of 100µg/l. The City of Saint John is continuing to collect data through THM surveys, analyze data and pursue opportunities (cleaning and lining of pipe infrastructure, watermain flushing, unidirectional flushing) of THM formation reduction.

At the root of this water quality problem is the inability to remove naturally occurring organic matter from the water before it is disinfected with chlorine. New treatment technologies can remove much of the organic matter prior to disinfection, thus reducing the levels of by-products while maintaining sufficient levels of disinfection to kill or inactivate microorganisms. The City of Saint John recently completed the preliminary design of water treatment facility.

 

If you are connected to the Saint John Water municipal water system, Saint John Water staff are available at 658-4455.

 

 

Individuals on municipal water supplies do not need to have their water supply tested because the City of Saint John regularly monitors water quality. Saint John Water currently uses Maxxam Analytics whom is a CALA (Canadian Association of Laboratory Accreditation) accredited laboratory.

If you have a private well that does not mix chlorine with the water, there should be no need to test for THMs. However, if you wish to have your water tested, please visit the following websites, to obtain the list of accredited labs, as well as to obtain the proper sampling vial as well as information on how to properly collect a representative water sample: CALA Directory of Laboratories at http://209.90.159.196/search.php?wId=s or Standards Council of Canada at http://palcan.scc.ca/SpecsSearch/TLSearchForm.do.