Page 4: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Vinyl Chloride
Part I. Overview and Application (continued)
Note: Specific guidance related to the implementation of drinking water guidelines should be obtained from the appropriate drinking water authority in the affected jurisdiction.
Vinyl chloride is a human carcinogen, which means that exposure to any level in drinking water may increase the risk of cancer. Jurisdictions may establish more stringent limits than the MAC.
Generally, vinyl chloride is not a concern for the majority of Canadians who rely on surface water as their source of drinking water, because it volatilizes easily. However, as vinyl chloride released to the ground does not adsorb onto soil, any that does not evaporate migrates readily to groundwater, where it is expected to remain for months to years. Vinyl chloride is usually only detected in groundwater in the vicinity of landfills and where there have been spills of vinyl chloride or chlorinated precursor compounds.
Vinyl chloride may also leach from polyvinyl chloride pipes used in the distribution and plumbing systems. To minimize levels of vinyl chloride from these systems, materials in contact with drinking water should be certified to ANSI/NSF Standard 61.
The drinking water guideline is based on lifetime exposure (70 years) to vinyl chloride from drinking water. For drinking water supplies that occasionally experience short-term exceedances above the guideline value, it is suggested that a plan be developed and implemented to address these situations. For more significant, long-term exceedances that cannot be addressed through treatment, it is suggested that alternative sources of water for drinking, showering, and bathing be considered. For infants less than 5 weeks of age, who may be more sensitive to the health effects of vinyl chloride, concentrations in drinking water should be kept as low as reasonably achievable.
The guideline for a carcinogen is normally established at a level at which the increased cancer risk is "essentially negligible" when a person is exposed at that level in drinking water over a lifetime. In the context of drinking water guidelines, Health Canada has defined this term as a range from one new cancer above background levels per 100 000 people to one new cancer above background levels per 1 million people (i.e., 10−5 -10−6 ). The estimated lifetime risk associated with ingestion of water containing vinyl chloride at the MAC is 5.0 × 10-5 which is above the range that is considered to represent "essentially negligible" risk. However, the MAC for vinyl chloride is a risk-managed value based on analytical achievability. Considering that it exceeds the health-based value, every effort should be made to maintain vinyl chloride levels in drinking water as low as reasonably achievable (or ALARA).
Groundwater sources should be characterized to determine if vinyl chloride is present, especially if the land use history is unknown. Quarterly monitoring for vinyl chloride should be conducted for groundwater sources that are or may have been impacted by landfill leachate, spills of vinyl chloride or chlorinated VOCs.
Although newer pipes and components are required to meet standards that limit leaching of contaminants, polyvinyl chloride water mains manufactured prior to 1977 are prone to leaching vinyl chloride because they often contain higher concentrations of unpolymerized vinyl chloride monomer.
It is recommended that distribution systems with these older PVC pipes be monitored for vinyl chloride. Quarterly monitoring for vinyl chloride should be undertaken in the areas of the distribution system where older PVC pipes are located, specifically at locations with the maximum residence time (e.g., dead ends). Utilities that have baseline data indicating that vinyl chloride is not present within the distribution system may conduct less frequent monitoring. Jurisdictions may consider reduced sampling if an appropriate flushing protocol is in place. In the event that monitoring data show elevated levels vinyl chloride, it is suggested that a plan be developed and implemented to address these situations.
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