Canadian Environmental Health Atlas

Understanding Our Environment is Key to Promoting Health and Preventing Disease

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Arsenic is found naturally in the Earth’s crust along with other elements (Figure 1). Human activities such as mining and smelting can release arsenic into the environment. In Canada, sites with high arsenic levels include Moira Lake, Ontario, Yellowknife, NWT, Bathurst, New Brunswick, and Rabbit Lake, Saskatchewan.1

Arsenic is odourless and colourless. Historically it was used as a poison. Today there is increasing evidence that long-term, low-level exposure to arsenic is associated with cognitive deficits, preterm birth, cardiovascular disease, and cancer. Exposure to arsenic is primarily through food, drinking water, and industrial pollutants.2 The government of Ontario has estimated that 84% of daily arsenic intake is from food, 15% from water, and less than 1% from soil or dust.3 Shellfish, meat, poultry, rice, and dairy products are potential food sources of arsenic.

Drinking water can be a significant source of arsenic in regions with naturally high concentrations of the element. Water from wells drilled into arsenic-rich bedrock can contain high levels of arsenic. Areas in Canada with rich arsenic deposits include parts of Yukon, northern BC, Nunavut, Atlantic Canada, and southern Ontario.2

Levels of Exposure

Worldwide, arsenic concentrations in water supplies vary from 0.00002 mg/L to more than 5 mg/L.1 Generally, drinking water in Canada has less than 0.0005 mg/L of arsenic.4 However, drinking water obtained from certain groundwater sources can have much higher concentrations of arsenic. The Canadian maximum acceptable concentration (MAC) for arsenic in drinking water is 0.010 mg/L, which is equivalent to 10 parts per billion.5