Arsenic Environmental Exposures


Consuming arsenic through food is generally considered the primary route of exposure for the general population, although drinking water can also be a significant source in areas where arsenic is found in bedrock (thus contaminating drinking water sources).[1]


Areas in Canada with arsenic-rich geologic deposits include the Yukon, Northern British Columbia (B.C.), Nunavut Islands, the Atlantic coast, and few hot spots in Southern Ontario.[2] CAREX Canada’s environmental estimates indicate that arsenic levels in Canadian drinking water result in higher risks of cancer at a population level (moderate data quality). Estimates for food and beverages show that arsenic exposure also results in an increased risk via this route (low data quality).

Quantifying the relative contribution of food and drinking water is difficult because arsenic uptake varies based on the form (i.e. organic or inorganic) and valence state of arsenic.[3] Based on limited available research,[4,5] intake of inorganic arsenic, which is considered more toxic, is estimated at 25% of total arsenic intake. In Canada, sources of arsenic in food include shellfish, meat, poultry, grain, and dairy products.[6] Arsenic has been found in bioaccessible forms (i.e. that can be readily absorbed) in Canadian wild plants and game, including berries, mushrooms, and hares.[7] In Ontario, 84% of the daily intake of arsenic was estimated to come from food, 15% from water, less than 1% from soils/dusts, and a negligible amount from skin contact.[6] This trend should be relatively similar across Canada. Arsenic in pigments and paints may be ingested through contaminated hands, fingernails, food, cups, or cigarettes.[8]

The average arsenic concentration in ambient air in 11 Canadian cities and one rural site in 1990 was 0.001 µg/m3.[3] Weathering and erosion of arsenic-containing rocks and soils contributes to natural levels of arsenic in the environment, however anthropogenic sources are the most significant contributors. Examples include mining base-metals and producing gold;[9] burning waste and
coal;[10] leaching from arsenic treated sawdust and wood, or smoke from treated wood;[8] and applying arsenic-based pesticides.[11] Monosodium methanearsonate (MSMA), an arsenic-containing pesticide, was used in B.C. forests from 1995-2004 in an attempt to slow the pine beetle infestation.[12] When arsenic accumulation and behavioural changes in woodpeckers and other insect-feeding species were observed, MSMA was removed from B.C. markets.[13]

Some Canadian sites with high arsenic levels from mining/smelting residues include Moira Lake, ON, Yellowknife, NT, Bathurst, NB, and Rabbit Lake, SK.[11] Samples taken recently near Sydney, NS found 20% of background soil samples and 95% of tar pond soil samples were above Canadian health-based guidelines for arsenic in soil .[14]

Searches of Environment Canada’s National Pollutant Release Inventory (NPRI) and the US Household Products Database yielded the following results on current potential for exposure to arsenic in Canada:

NPRI and US Household Products Database

NPRI 2015[15]
Substance name: ‘Arsenic’
Released into Environment152 tFoundries,
Non-ferrous metal (except aluminum)
production and processing,
metal ore mining (272 facilities)
Disposed of23,889 t
Sent to off-site recycling473 t
US Household Products 2015[16]
Search TermQuantityProduct Type
‘Arsenic’6Gear and motor oils (4), cement colorant (1), pet care lotion(1)
t = tonne


This map shows predicted levels of arsenic in outdoor air at residential locations by health region in Canada as of 2011. The average (median) concentration of arsenic within the health regions measured in outdoor air for 2011 was 0.0006 µg/m3, but concentrations of arsenic can be higher or lower than average in many locations. Concentrations should be compared to the applicable jurisdictional guidelines and standards for ambient air quality based on chronic, carcinogenic effects (or non-carcinogenic effects, if cancer is not the point of interest).

Predicted annual average arsenic concentrations in outdoor air at residential locations by health region, 2011

*Measured at the National Air Pollution Surveillance (NAPS) monitors in 2011

Cancer Risk Estimates

Potential lifetime excess cancer risk (LECR) is an indicator of Canadians’ exposure to known or suspected carcinogens in the environment. When potential LECR is more than 1 per million in a single pathway, a more detailed risk assessment may be useful for confirming the need to reduce individual exposure. If measured levels of arsenic in relevant exposure pathways (outdoor air, indoor air, indoor dust, drinking water, and food and beverages) decrease, the risk will also decrease.

Potential LECR is calculated by multiplying lifetime average daily intake (the amount inhaled or ingested) by a cancer potency factor or unit risk factor. More than one cancer potency factor may be available, because agencies interpret the underlying health studies differently, or use a more precautionary approach. Our results use cancer potency factors from Health Canada, the US Environmental Protection Agency (US EPA), and/or the California Office of Environmental Health Hazard Assessment (OEHHA).

The calculated lifetime daily intake and LECR results for arsenic are provided in the tables below. For more information on supporting data and sources, click on the Methods and Data tab below.

Calculated Lifetime Daily Intake

Lifetime Excess Cancer Risk (per million people)

*LECR based on average intake x cancer potency factor from each agency

Compare substances: Canadian Potential Lifetime Excess Cancer Risk, 2011

The data in this table are based on average intake and Health Canada’s cancer potency factor, assuming no change in measured levels. When Health Canada values are not available, United States Environmental Protection Agency values are used.
Click the second tab to view LECR data. 

**Exposure not applicable: For indicated pathways, substance not present, not carcinogenic, or exposure is negligible
**Gap in data: No cancer potency factor or unit risk factor, or no data available
IARC Group 1 = Carcinogenic to humans, IARC Group 2A = Probably carcinogenic to humans, IARC Group 2B = Possibly carcinogenic to humans
NOTE: Chromium (hexavalent) estimates assume that 5% of total chromium measured in outdoor air is hexavalent and 8% total chromium measured in indoor dust is hexavalent. 

Potential LECR assumes exposure occurs at the same level, 24 hours per day, for 70 years. This is rarely true for any single individual, but using a standard set of assumptions allows us to provide a relative ranking for known and suspected carcinogens across different exposure routes. While ongoing research continually provides new evidence about cancer potency and whether there is a safe threshold of exposure, our approach assumes there are no safe exposure levels.

Methods and Data

Our Environmental Approach page outlines the general approach used to calculate lifetime excess cancer risk estimates and includes documentation on our mapping methods.

Data sources and data quality for arsenic can be found in the PDF below.

Supplemental data – Arsenic [PDF]


2. Grosz AE, Grossman JN, Garette R, Vowinkel E. “A preliminary geochemical map for arsenic in surficial materials of Canada and the United States” Appl Geochem 2004;19:257-260
4. Hazell T. “Minerals in foods: dietary sources, chemical forms, interactions, bioavailability.” World Review of Nutrition and Dietetics1985;46:1.
5. EPA (1988). Special report on ingested inorganic arsenic. Skin cancer; nutritional essentiality. Report No. EPA-625/3-87/013, Risk Assessment Forum, U.S. Environmental Protection Agency, Washington, DC.
6. Canadian Environmental Health Atlas. Arsenic
7. Koch I, Dee J, House K, Sui J, Zhang J, McKnight-Whitford A, Reimer KJ. “Bioaccessibility and speciation of arsenic in country foods from contaminated sites in Canada.” Sci Total Environ 2013;449(1).
8. National Toxicology Program (NTP). 14th report on carcinogens for Arsenic Compounds, Inorganic (2016) (PDF)
11. Wang S, Mulligan C. “Occurrence of arsenic contamination in Canada: Sources, behaviour and distribution.” Sci Tot Environ2006; 366(2-3):701-721.
12. US Geological Survey. Arsenic Yearbook (2007) (PDF)
13. Morrissey C, Dods P, Elliott J. “Pesticide Treatments Affect Mountain Pine Beetle Abundance and Woodpecker Foraging Behavior.” Ecological Applications 2008;18(1):172-184.
15. Environment and Climate Change Canada. National Pollutant Release Inventory (NPRI) Facility Search (Substance name: ‘Arsenic’)
16. US National Library of Medicine. Household Products Database (HPD) (Search term: ‘Arsenic’)


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