August 30th, 2000



Warning: Government Advice Risks Public Arsenic Poisoning

On August 26, the Ontario government Ministry of Environment and the Medical Officer of Health for Hastings and Prince Edward Counties Health Unit issued a “drinking water reminder” to the public who might be drawing water from the Moira River in Eastern Ontario, which if followed, could lead to arsenic poisoning.

The contaminated section of the Moira River flows through or close to the communities of Deloro, Madoc, Tweed, Roslin, Plainfield, Corbyville, and Belleville. Along its course, the river forms three lakes, Bend Bay, Moira Lake and Stocco Lake before entering the Bay of Quinte on Lake Ontario. From Deloro to the discharge from Moira Lake, annual average arsenic concentrations exceeded or nearly exceeded the existing provincial water quality standards in 1988, 1991 and 1999. The existing provincial water quality standard is twice the current standard in the U.S. and 20 times higher than the Ontario government’s proposed interim objective and the level the U.S. Environmental Protection Agency is proposing in the U.S. based on public health risks from arsenic in drinking water. The interim objective level has not been met on an annual average basis since industrial operations were established at Deloro.

Arsenic is both a chronic and an acute toxin known to cause cancer and other serious diseases. Arsenic levels in the river downstream of Deloro are highly influenced by the dilution capacity of the river’s flow. Particularly during periods of low rainfall in summer when recreational usage is most active, arsenic concentrations in grab samples, similar to the way water is drawn for drinking, are known to exceed the current lax provincial water quality objective. In recent years, the highest published grab sample was 2 times the provincial standard or 40 times the proposed standard. The occurrence of higher, but undocumented, concentrations cannot be ruled out.

Referencing only the average annual concentrations of arsenic and not concentration spikes, which are know to be prevalent, the Ontario government and the Medical Officer of Health for the area, on August 26 issued a summary of an impact study on the river that includes a “drinking water reminder” advising those drawing water from the river between Deloro and the discharge from Moira Lake “not to drink untreated lake or river water.” Following a lay person’s understanding of this advice could be harmful.

Conventional household water treatment methods, such as boiling or filtration through household water filters available in hardware stores, are not effective in removing arsenic dissolved in drinking water. Household water filters typically use activated carbon and ion exchange resins that are capable of capturing carbon-based contaminants and dissolved metals like lead and copper that carry positive charges but not arsenic that carries a negative charge. Methods of treating arsenic contaminated water to make it safe for drinking include advanced reverse osmosis technology and sequential ion exchange technology. Additional information on treatment options can be found at Treated water should be assayed through approved laboratory procedures to ensure purity before being used for human consumption. These treatment and assay methods are not likely to be available to ordinary households.

The Ontario government has operated a heavy metal disposal site on the Moira River in the Village of Deloro since 1979. According to the government’s own analysis, in 1996 for example approximately 3270 kilograms of soluble arsenic were discharged into the Moira River from the site.

The Ontario government’s advice “not to drink untreated lake or river water” downstream of their disposal site operations was issued as a result of an impact study on the river. Further analysis of the impact study will be forthcoming on the Environmental Bureau of Investigation web site at

For more details please see the recent article Water warning to come next year.

For further information contact:
Janet Fletcher, Advisory Panel Member
Environmental Bureau of Investigation
Tel: 613-533-6000 ext. 77720, or 613-546-7869 E-mail:
Dr. Lynn Noseworthy, Medical Officer of Health for Hastings and Prince Edward Counties Health Unit, Belleville
Tel: 613-966-5500
Wayne Herrick, Barbara Theman or Heather Hawthorne, Ministry of the Environment, Kingston Tel: 1-800-267-0974 or 613-549-4000