Findings

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The heavy metals lead, mercury and cadmium are widely dispersed in the environment, and at excessive levels, are toxic to humans.¹ Chronic exposure to these substances may also be hazardous. Although these metals occur naturally, exposure may be increased by human activities that release them into the air, soil, water and food, and by products that contain heavy metals.

This article presents preliminary data on blood levels of lead, total mercury, and cadmium in Canadians from the new Canadian Health Measures Survey (CHMS). These preliminary results are based on 8 collection sites from the CHMS. Results based on data from all 15 sites will be available in 2010.

The CHMS was launched by Statistics Canada in partnership with Health Canada and the Public Health Agency of Canada to collect data from approximately 5,000 Canadians aged 6 to 79 at 15 sites across Canada from March, 2007 to March, 2009. The CHMS entails an in-home general health interview and a subsequent visit to a mobile clinic where direct physical measures, including blood and urine samples, are taken.

The blood and urine samples are used to test for infectious diseases, nutritional status and cardiovascular disease risk factors, and also, for biomonitoring—that is, to measure levels of environmental chemicals. This biomonitoring component of the CHMS will help meet the need for nationally representative data on current population levels for a broad range of environmental chemicals, provide a baseline for emerging trends, and allow comparisons with other countries.

Lead

Sources of lead exposure include lead-based paint, lead plumbing, food grown in lead-contaminated soil, and toys, fuels or other products that contain lead or lead-based paints. Exposure to high lead levels can severely damage the brain and kidneys. Chronic exposure can result in decreased neurological performance. In pregnant women, exposure to high lead levels may cause miscarriage, and chronic exposure may affect the development of the foetus.¹⁹

Preliminary results from the CHMS show that the geometric mean blood lead concentration of Canadians is 1.37µg/dL (Table 1). Over 99% of Canadians aged 6 to 79 have measurable amounts of lead, that is, levels above the laboratory test method's limit of detection of 0.02µg/dL. However, having a measurable amount of lead in the blood does not necessarily mean that it will cause adverse health effects. Indeed, the current Health Canada blood lead guidance value for the general population is 10µg/dL.²⁰ A guidance value is the level above which follow-up actions may be considered to reduce exposure.

Fewer than 1% of the population have blood lead concentrations above the current Health Canada guidance value. (The coefficient of variation for this estimate was too high to reliably report a specific value.) This is a noticeable decline from 1978 to 1979 when results of the Canada Health Survey showed that 25% of Canadians aged 6 or older had blood lead concentrations above 10µg/dL.²¹ Much of this decline may reflect the phase-out of leaded gasoline, lead-containing paints, and lead solder in food cans since the 1970s.²²

The United States and Germany are among the few countries that have conducted nationally representative biomonitoring surveys that include testing for heavy metals. In the United States, the 2001-2002 National Health and Nutrition Examination Survey (NHANES) reported blood lead levels for the population aged 1 or older.²³ The 1998 German Environmental Survey (GerES III) and 2003 to 2006 German Environmental Survey for Children (GerES IV) reported blood lead levels for adults aged 18 to 69 and children aged 6 to 14, respectively.^13, 24   Blood lead levels have also been reported from a survey of the non-occupationally exposed general population aged 18 to 65 in the Quebec City Region.¹⁴ A comparison of the geometric mean blood lead concentrations showed that Canadians overall have similar or slightly lower blood lead levels, compared with these populations (Table 2).

Total mercury

There are three chemical forms of mercury:  elemental, inorganic, and organic, notably, methylmercury. Exposure of the general population is primarily to methylmercury and occurs through the consumption of fish and seafood.²⁵ To a much lesser extent, the general population is exposed to inorganic mercury through dental amalgams.²⁵ Previous studies have shown that inorganic mercury comprises 14% to 26% of total blood mercury.^26-28 Thus, a measurement of total blood mercury consists primarily of methylmercury.

Chronic exposure to methylmercury may cause numbness and tingling in the extremities, blurred vision, deafness, lack of muscle coordination and intellectual impairment, as well as adverse effects on the cardiovascular, gastrointestinal and reproductive systems. Prenatal exposure may interfere with foetal development of the central nervous system and cause neurological and developmental delays. Women who are exposed to methylmercury and breastfeed may also expose the child through the milk.²⁹

Preliminary CHMS results show that the geometric mean blood mercury level of Canadians aged 6 to 79 is 0.76µg/L (Table 3), with approximately 90% having concentrations above the limit of detection of 0.10µg/L. (Because the coefficient of variation for this estimate was between 16.6% and 33.3%, it should be interpreted with caution.) However, fewer than 1% of Canadians aged 20 to 79 have total mercury concentrations above the current Health Canada blood guidance value of 20 µg/L³⁰ established for the general adult population. (The coefficient of variation for this estimate was too high to reliably report a specific value.)

A comparison of the geometric mean blood mercury concentrations shows that Canadians overall have similar or slightly higher levels than those of the general population in Germany,^13, 24 females aged 16 to 49 in the United States,²³ and a non-occupationally exposed population in the Quebec City region¹⁴ (Table 2).

Cadmium

Sources of exposure to cadmium include diet, drinking water and occupational exposure. For the non-occupationally exposed population, cigarette smoking is considered to be a major source of exposure.^31, 32 

Chronic exposure to cadmium may cause kidney damage, bone mineral density loss and hypertension.^32, 33 Acute and chronic inhalation of cadmium can cause potentially fatal pulmonary dysfunction.³² In addition, cadmium has been classified as carcinogenic by the International Agency for Research on Cancer, with exposure being primarily associated with lung cancer.³⁴

According to preliminary CHMS results, the geometric mean blood cadmium of Canadians aged 6 to 79 is 0.35µg/L, with about 98% having levels above the limit of detection of 0.04µg/L (Table 4). No Canadian blood cadmium guidance value has been established for the general population. Occupational exposure guidance values exist, but they are not applicable to the population overall. Previous research has shown that cigarette smoking can raise blood cadmium to levels that are at least 2.5 to 4 times higher than in non-smokers,^13-15 but because of the small sample size, such associations could not be examined in this article.

A comparison of the geometric mean blood cadmium concentrations shows that Canadians' blood cadmium levels are similar to those of the general population of the United States²³ and Germany,^13, 24 and a non-occupationally exposed population in the Quebec City region¹⁴ (Table 2).

Summary

These preliminary findings from the Canadian Health Measures Survey provide national population estimates for blood lead levels, which have not been measured since 1978, as well as the first national population estimates for total mercury and cadmium levels. While most Canadians have measurable amounts of these heavy metals in their blood, this does not necessarily mean that they experience adverse health effects. Indeed, fewer than 1% of Canadians aged 6 to 79 have blood lead levels above the current Health Canada general population guidance value of 10µg/dL, and fewer than 1% of those aged 20 to 79 have total blood mercury levels above the Health Canada guidance value of 20µg/L for the general adult population. Canadians' levels of lead, total mercury and cadmium are similar to those of people in the United States²³ and Germany.^13 24

Further information about the CHMS can be found at:

• Statistics Canada

Further information about biomonitoring, and specifically, lead, mercury and cadmium, their health effects, and ways to minimize exposure can be found at:

• Health Canada
• Chemical Substances in Canada