Health Canada has issued two guideline values this month for manganese in drinking water.
Manganese is an essential element for humans that occurs naturally in the environment and is widely distributed in air, water and soil.
Health Canada worked with provinces, territories and other federal departments to set a new guideline value for manganese in drinking water of 0.12 milligrams per litre (mg/L). Manganese has long been considered to be an aesthetic concern in drinking water due to water discoloration that can stain laundry or fixtures. In response, Health Canada established an aesthetic objective of 0.02 mg/L.
From a global perspective, Canada’s health-based guidelines are some of the lower limits for manganese. The U.S. has set 0.3 mg/L; Australia has set 0.5 mg/L; and the World Health Organization recommends 0.4 mg/L, but no formal guideline was established.
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“Considering that manganese levels can vary significantly in source water and within treatment plants and distribution systems, it is necessary to design system-specific monitoring programs that enable utilities to have a good understanding of manganese levels from source to tap,” states the new Canadian guidelines.
The guidelines add that, while manganese concentrations in groundwater are less likely to fluctuate between seasons, large variations have been observed between wells located in close proximity to each other.
“The best way to protect yourself and your family from exposure to bacteria and chemicals is to test your well water regularly and treat it when needed,” announced Dr. Robert Strang, chief medical officer of health in Nova Scotia, in a statement ahead of the new guidelines.
More than 40% of Nova Scotia households get their drinking water from private wells, Strang notes. Well water should be tested every six months for bacteria and every two years for chemical contaminants.
Monitoring of surface water should be conducted quarterly, with weekly monitoring being done during summer and fall in lakes and reservoirs subject to stratification or large fluctuations in manganese concentrations. Groundwater sources should be monitored semi-annually, suggests the new guidelines.
“Authorities may consider reduced monitoring when it has been demonstrated that manganese is present at concentrations equal to or below 0.02 mg/L in the source water and/or appropriate treatment is in place,” states the new guidelines. “It is also worth noting that iron and manganese often co-occur in source water and can also cause water discolouration. Therefore, it is recommended that utilities determine if iron is also present in the source water.”
The new guidelines recommend that dissolved manganese as Mn(II) can be removed or controlled by source water practices, oxidation/physical separation, adsorption/oxidation, biological filtration, and precipitative softening.
The guideline technical document for manganese in Canada can be found here.
Some communities have been preparing ahead of the new guideline values, particularly if levels were found to be above the 0.12 milligrams per litre (mg/L) threshold.