Page 2: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Trihalomethanes
The guideline technical document (GTD) for trihalomethanes (THMs), which was published in 2006, also includes a specific guideline for bromodichloromethane (BDCM). The maximum acceptable concentration (MAC) for THMs is based on the health effects of chloroform, and applies to the total concentration of chloroform, BDCM, dibromochloromethane and bromoform.
Since the publication of the GTD, several new scientific papers have been published on the health effects of BDCM and of THMs. As these articles were considered to have a potential bearing on the existing guideline values, a panel of experts was convened in September 2008 to provide expert advice and to make recommendations to Health Canada and to the Federal- Provincial-Territorial Committee on Drinking Water (CDW) regarding BDCM in drinking water.
Based on Health Canada's re-assessment of the overall weight of scientific evidence and on the findings and recommendations of the Expert Panel 5 on BDCM, the Federal- Provincial-Territorial CDW recommended rescinding the separate guideline for BDCM. The guideline for THMs is now considered sufficient on its own to protect for potential adverse health effects related to the exposure to BDCM in drinking water. The new information on BDCM will be added in the GTD for THMs during the next update of the document.
Effective April 2009, the guideline statement for trihalomethanes in drinking water is modified to remove the separate guideline for BDCM, recognizing that the maximum acceptable concentration for
THMs is protective of the health effects of all THMs, including BDCM.
The revised Guideline statement reads as follows:
The maximum acceptable concentration (MAC) for trihalomethanes (THMs) in drinking water is 0.100 mg/L (100 :g/L) based on a locational running annual average of a minimum of quarterly samples taken at the point in the distribution system with the highest potential THM levels.
Utilities should make every effort to maintain concentrations as low as reasonably achievable without compromising the effectiveness of disinfection.
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