Monitoring Blood Lead Levels
Over the past three decades, there has been a dramatic reduction in blood lead levels in North America. In the 1970s, the typical American child had a blood lead level of about 15 μg/dL. Blood lead levels plummeted following the phase-out of leaded gasoline, a reduction that was much greater than anticipated (Figure 1). Similarly, in the Canadian Health Survey conducted in the 1970s, the mean blood lead levels of Canadians was 4.79 μg/dL; about 25% of Canadians older than 6 years had blood lead levels above 10 μg/dL.1 By 2009, the mean blood lead level was 1.34 μg/dL (Figure 2); fewer than 3% had concentrations above 5 μg/dL.2 This reflects the impact of public health measures, such as phasing out leaded gasoline and banning lead in paints and food cans.
Canadian Blood Lead Levels Today
Biomonitoring data collected in the Canadian Health Measures Survey (CHMS) provides an assessment of contaminant levels in Canadians. This national survey collects health information from about 5,000 Canadians between the ages of 6 and 79 using home interviews and physical measurements; children in the 3 to 6 years range will be included in future surveys.2Samples of blood are collected from study participants to evaluate both recent lead exposures from the environment and past exposures related to lead released from bone to blood.
Persistence of Lead
Environmental sources of lead persist in Canada. The geometric mean blood lead concentration of Canadians surveyed was 1.34 μg/dL; 100% of Canadians tested had measurable amounts of lead in their blood.2 Concentrations of blood lead were highest among older adults, likely due to past environmental exposures and release of lead with age-related bone loss. Males had higher concentrations of lead in their blood than females for all groups except the 6- to 11- year-old children, probably because of the higher exposures men experience in the workplace.
Role of Other Factors
The Canadian Health Measures Survey also found that members of low-income households had higher blood lead concentrations (1.49 μg/dL) than those in the highest income households (1.27 μg/dL). This is mostly due to higher exposures as well as nutrition deficiencies (e.g. too little iron or calcium), which can make people absorb lead more readily.
The survey also showed that people born outside of Canada had higher concentrations of lead in their blood than those born in Canada (1.54 μg/dL compared to 1.29 μg/dL). Foreign-born people often immigrate from countries where environmental lead exposure is more common or they may live in older, poorly maintained housing in Canada.
Although we can take some comfort in the dramatic decline from the peak exposures that occurred during the 1960s, our blood lead levels are still 10 to 100 times higher than those of our pre-industrial ancestors. More work is needed to further reduce the risk of exposure.
- 1. Health and Welfare Canada, Statistics Canada. The health of Canadians: Report of the Canada Health Survey (Statistics Canada, Catalogue 82- 538E). Ottawa: Statistics Canada; 1981.
- 2. a. b. c. Bushnik T, Haines D, Levallois P, et al. Lead and bisphenol A concentrations in the canadian population. Ottawa: Statistics Canada; 2010. www.statcan.gc.ca/pub/82-003-x/2010003/article/11324-eng.htm.