Canada is proposing a risk-managed approach that would reaffirm a maximum acceptable concentration (MAC) of 0.006 mg/L (or 6 µg/L) for antimony in drinking water that was developed in 1999.
Antimony (Sb) is a metal naturally present in small quantities in water, rocks and soils. It can be harmful to the gastrointestinal system and the liver, as well as harmful to the eyes and skin and cause problems with the kidneys.
The MAC for antimony is being revisited by the Federal-Provincial-Territorial Committee on Drinking Water, particularly in relation to private wells and for small systems, where some have suggested that lowering the MAC could significantly increase health protection.
The proposed guideline technical document (available for comment until March 8) however, suggests that lowering the MAC would not provide additional protection, although its authors note that they will continue to monitor new research in the area and recommend any changes.
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“At the municipal level, treatment technologies that are available to achieve antimony drinking water concentrations below the proposed MAC include coagulation, adsorption, membrane filtration and coagulation followed by ultrafiltration,” states the newly-proposed guideline.
In water monitoring data obtained from the provinces, antimony detection frequency was very low, indicating that a large number of the samples had antimony concentrations below the detection limit, states the document published in the December edition of the Canada Gazette.
The National Drinking Water Survey of Canada had maximum antimony concentrations below 1.0 μg/L during the summer months, but had some higher concentrations in the raw and treated lake water during the winter months. There were slight differences between raw, treated and distribution system waters.
Monitoring for total antimony and other contaminants (e.g., iron, manganese, arsenic, lead) should be conducted when water quality changes or physical disruptions occur in the system, recommends the guidance document.
“The release of antimony and other contaminants may be indicated by the presence of discoloured water or increased turbidity resulting from the release of deposits or scales present on the pipe wall,” states the guideline.
Antimony can come naturally from windblown dust, weathering of mineral rocks — predominantly sulphides and sulphosalts, or volcanic ash. It can also come from coal combustion, including mining and smelting, or from busy vehicle areas in the form of abrasions in tires and brake linings.
Antimony, minimally produced in Canada, is absorbed by the roots of vegetables and other crops grown on antimony-containing soils; however, dietary exposure to total antimony is low. PET (polyethylene terephthalate) food packaging materials, such as trays and bottles, may also contribute to antimony in food, the new document states.
Other sources of antimony include fire retardants, shooting ranges, pharmaceuticals and pesticides. It may also enter drinking water from plumbing solders in drinking water distribution systems.
Over 200 inorganic compounds of antimony exist in the environment, with stibnite being the most abundant, followed by the oxides of antimony and the antimonides of heavy metals, with arsenic being the most predominant.
At the residential scale, certified treatment devices relying on reverse osmosis and distillation have proven most effective for the removal of antimony.
