Page 6: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Arsenic
Levels of inorganic arsenic are generally higher in groundwater sources than in surface water. Where arsenic is found in surface water, some organic forms may be present (U.S. NRC, 1999). Monitoring data for water supplies have been submitted by several Canadian provinces. Arsenic levels ranged from 0.1 to 26.0 µg/L in groundwater supplies in Prince Edward Island between 1986 and 2002; levels in greater than 99% of samples were below 10 µg/L, the average being approximately 1.5 µg/L (Prince Edward Island Department of Fisheries, Aquaculture and Environment, 2003).
In Quebec, arsenic levels ranged from 1.0 to 25.0 µg/L in municipal treated surface water in 523 communities for 1990-2002; levels in more than 99% of samples were less than 10 µg/L, the annual average being 1.6 µg/L. Levels ranged from 1.0 to 60 µg/L in municipal treated groundwater in 562 communities for the same period; approximately 98% of samples contained levels less than 10 µg/L, the annual average being 2.0 µg/L (Ministère de l'Environnement du Québec, 2003).
In Ontario, arsenic levels ranged from 0.1 to 18 µg/L in treated groundwater and surface water in 726 communities for 1997-2002. Levels in more than 99% of samples were less than 10 µg/L, the annual average being less than or equal to 0.7 µg/L (Ontario Ministry of Environment and Energy, 2003). Ontario monitoring data submitted by private laboratories indicated that arsenic levels in treated and raw drinking water ranged from less than 2.5 to 68 µg/L for the period 1999-2002, the average value being less than 2.5 µg/L. The higher values came predominantly from wells (Ontario Ministry of Environment and Energy, 2003).
In Saskatchewan, arsenic levels ranged from 0.5 to 105.0 µg/L in municipal treated water supplies in 539 communities between 1976 and 2002; concentrations in 97% of samples were less than or equal to 10 µg/L, the average being 3.0 µg/L (Saskatchewan Department of Environment and Resource Management, 2003). Arsenic levels ranged from 0.1 to 1000 µg/L in treated groundwater and surface water in 573 Alberta communities for 1980-2002. Approximately 99% of samples contained less than 10 µg/L, the annual average being 1.8 µg/L (Alberta Department of Environment, 2003).
Elevated arsenic concentrations have been reported in areas with natural sources. In Nova Scotia, 9% of well water samples tested for arsenic at the Environmental Chemistry Laboratory in Halifax between 1991 and 1997 exceeded 25 µg/L (Nova Scotia Department of the Environment, 1998). Méranger et al. (1984) reported that levels exceeded 50 µg/L in 33-93% of wells in each of seven communities in Nova Scotia; concentrations were greater than 500 µg/L in 10% of the wells sampled (n = 94). In Newfoundland, maximum arsenic levels ranged from 6 to 288 µg/L in public water supplies (54 wells) in 2002. Public schools (n = 16) with their own water supplies had levels ranging from 1 to 368 µg/L; approximately 19% of school wells had maximum levels above 10 µg/L (Newfoundland Department of Environment and Labour, 2003). In British Columbia, a maximum arsenic concentration of 580 µg/L was reported in groundwater samples taken on Bowen Island (Boyle et al., 1998).
Some western U.S. states with volcanic rock and sulphidic mineral deposits have arsenic levels in groundwater exceeding 3 mg/L (ATSDR, 2000). Elevated levels of arsenic in drinking water from wells in the northern provinces of Argentina have been reported; in Médanos in Buenos Aires Province and La Francia in Córdoba, concentrations as high as 2 mg/L and 12 mg/L, respectively, have been reported. Levels exceeded 1 mg/L at several other locations (Grinspan and Biagini, 1985).
On the basis of results indicating that the concentration of arsenic in drinking water in areas without natural sources is usually less than 5 µg/L and assuming that the average daily intake of drinking water is 1.5 L, the mean daily intake of arsenic from this source (in the predominantly pentavalent inorganic form) for an adult will generally be less than 7.5 µg. A child (0.5-4.0 years) with an average daily intake of 0.7 L of drinking water would consume less than 3.5 µg.
Food is generally considered the major source of arsenic exposure except in situations where a population is living near a point source (natural geological source or site of contamination). However, it is difficult to compare the intake of arsenic from food with that from drinking water, as the form (organic vs inorganic), valence, and biological availability of arsenic in these two sources vary.
Arsenic is concentrated by many species of fish and shellfish and is used as a feed additive for poultry and livestock; fish and meat are therefore the main sources of dietary intake (78.9%, according to a U.S. survey) (Gartrell et al., 1986). A 1997 British total diet study found that seafood contributed 94% of the total arsenic intake for the general population (U.K. MAFF, 1999). In Canada, arsenic levels ranging from 0.4 to 118 mg/kg have been reported in marine fish sold for human consumption, whereas concentrations in meat and poultry range up to 0.44 mg/kg (Department of National Health and Welfare, 1983). While organic arsenic compounds (e.g., arsenocholine and arsenobetaine) found in most seaweed and other marine foods have been determined to be relatively non-toxic (Sabbioni et al., 1991), toxic inorganic forms have been found in hijiki seaweed (CFIA, 2001). Levels in vegetation are generally an order of magnitude lower than those in fish, whereas concentrations in shellfish are often far higher than those in fish (Subramanian, 1988). Exogenous sources of arsenic in the diet potentially include arsenic-containing fungicides used in fruit production. In North America, however, arsenic-containing pesticides are no longer used on food (ATSDR, 2000; PMRA, 2003).
Recent estimates of the mean daily intake of total arsenic in food for adults are as follows: 42 µg (range 22.5-78.7 µg) for adults 20-65+ years old in Canada (Dabeka et al., 1993), 56 µg (range 27.5-92.1 µg) for adults 25-70+ years old in the United States (Tao and Bolger, 1998), 120 µg in the United Kingdom (U.K. MAFF, 1999), 150 µg in New Zealand (Vannoort et al., 1995), 286 µg in Spain (Urieta et al., 1996), and 182 µg in Japan (Mohri et al., 1990).
In children aged 1-4 and 5-11 years, mean daily intakes of total arsenic in food from six Canadian cities have been reported to be 14.9 µg (range 11.4-18.1 µg) and 29.9 µg (range 25.5-39.7 µg), respectively (Dabeka et al., 1993). Daily intakes of 2.15 µg, 23.4 µg, 20.3 µg, and 13.3 µg have been reported for children aged 6-11 months, 2 years, 6 years, and 10 years, respectively, in the United States (Tao and Bolger, 1998).
With regard to food preparation, the U.S. Environmental Protection Agency (EPA) estimates that preparing foods with arsenic-containing water may increase arsenic content by as much as 10-30% for most foods; beans and grains that absorb water when cooked may absorb up to 200-250% (Mead, 2005).
Ambient levels of arsenic in air in 11 Canadian cities and one rural site for the period 1985-1990 ranged from <0.0005 to 0.017 µg/m3 (24-hour average), the mean for cities being 0.001 µg/m3 (Dann, 1990). Higher atmospheric concentrations are normally found near metal smelters. In Yellowknife in 1997, concentrations ranged from 0.002 to 0.063 µg/m3, with an annual average of 0.005 µg/m3 (Government of the Northwest Territories, 1998).
In the United States, average annual arsenic concentrations in air have been reported to be 0.4 ng/m3 in rural areas remote from smelting activities, 3 ng/m3 for all locations, and 30 ng/m3 in areas within 80 km of non-ferrous smelters (Ball et al., 1983). Concentrations of arsenic in indoor air in the presence of environmental tobacco smoke (ETS) ranged from <0.1 to 1 ng/m3, while sites that were ETS-free had concentrations below 0.13 ng/m3 (Landsberger and Wu, 1995).
Based on the Canadian (0.001 µg/m3) and U.S. (0.003 µg/m3) ambient air levels, intake of arsenic through inhalation (principally in the inorganic form) is likely to be negligible (<0.1 µg, assuming 16.2 m3 of air inhaled per day) for adults compared with the amount ingested (mainly in the organic form). Intake of arsenic (inorganic) for a child (1-4 years) based on the same ambient levels and an inhalation rate of 5 m3 of air per day would be less than 0.05 µg (Health Canada, 1998).
Arsenic in soil (predominantly inorganic) originates from underlying materials that form soils, industrial wastes, or the use of arsenical pesticides. In Canada, average concentrations of arsenic in soil range from 4.8 to 13.6 mg/kg (Kabata-Pendias and Pendias, 1984). U.S. background levels are similar, ranging from 1 to 40 mg/kg, with a mean of approximately 5 mg/kg (ATSDR, 2000). Significantly higher concentrations in soil have been found near smelters (means of 50-100 mg/kg), near gold mining operations (means of 60-110 mg/kg), in arsenical-treated soils (means up to 54 mg/kg), and at wood preservation sites (means up to 6000 mg/kg) (Environment Canada and Health and Welfare Canada, 1993). Generally, exposure from soil is potentially significant only in those circumstances where residential neighbourhood areas have been built in contaminated sectors.
While exposure to arsenic via soil is unlikely to be a concern for older children and adults, hand-to-mouth behaviour and intentional ingestion may result in significant exposure for young children. In unexposed and exposed populations, young children (=4 years) were estimated to be exposed to 0.02-0.05 and 0.01-1.9 µg/kg bw per day, respectively (Environment Canada and Health and Welfare Canada, 1993).
It is difficult to compare the intake of arsenic from food with that from drinking water, as the form (organic vs inorganic), valence, and biological availability of arsenic in these two sources vary. For example, a major portion of the organic arsenic in fish is present as highly complexed forms that are biologically unavailable (e.g., arsenobetaine) (Vahter et al., 1983; JECFA, 1988). The remainder is present largely as simple organic complexes, mainly trimethyl arsine, which are rapidly excreted from the body. Seafood contributes much of the daily arsenic intake, even where the consumption of fish is low (Hazell, 1985). On the basis of data on the organic and inorganic arsenic contents of various foodstuffs (Hazell, 1985; U.S. EPA, 1988), it can be estimated that approximately 25% of the intake of arsenic from food is inorganic and 75% is organic. Assuming that the average daily intake of arsenic from food is 42 µg, the daily intake of inorganic arsenic from food would be 10.5 µg. This contrasts with an intake of <7.5 µg of principally the pentavalent inorganic arsenic species in drinking water. Intake of inorganic arsenic for a child (1-4 years) based on an average daily intake of total arsenic from food of 14.9 µg would be approximately 3.7 µg, which is similar to the intake from drinking water for this age group (<3.5 µg).
Based on the above estimates for a typical population, the exposure media may be ranked in the following order of importance in terms of contributing to arsenic intake: food, drinking water, soil, and air. In a situation where a population is living near a point source (natural geological source or site of contamination), drinking water has been calculated to be the most important contributor to overall exposure (Environment Canada and Health and Welfare Canada, 1993).
Report a problem or mistake on this page
- Date modified: