What are Canadians made of?
Not snakes and snails and puppy-dog tails, or even sugar and spice, as the children’s rhyme goes. Try lead and bisphenol-A (BPA).
Statistics Canada’s report, Lead and Bisphenol A Concentrations in the Canadian Population, was released on August 16. The report details results of the 2007-2009 Canadian Health Measure Survey, in which concentrations of lead in whole blood and urinary BPA were reported for 5319 and 5476 Canadians, respectively, aged 6 to 79 years.
Good news: Blood lead levels are only about one-third what they were in the last survey, completed 30 years ago.
While we do not yet know what concentration of BPA poses a health risk, this study provides an excellent baseline for future research.
Below, we highlight some interesting results from the report:
Lead occurs naturally in rocks and soil, but was also used in gasoline, paints and as solder in food cans for decades. It is still used in certain car batteries and electronic equipment, and is sometimes found even in children’s jewellery and toys. Canadians are mainly exposed to lead via inhalation or ingestion (e.g., as dust particles from lead-based paint), through drinking water distributed via lead pipes or through occupations. Once absorbed, the metal accumulates in tissues and bone, or is excreted via urine and feces. Increased lead levels can harm the brain and kidney.
Lead exposure is measured by blood levels (PbB); this figure may be difficult to interpret as it can represent very recent exposure (lead’s half-life in blood is around 1 month), or exposure that occurred long ago, as lead leaches from bones (where its half-life may be decades) into the blood.
Although there is no known threshold below which lead is safe, PbB levels from 0.30 – <0.5 micromol/L are considered above average for Canadians. PbB levels at or above 10 mcg/dL (0.48 micromol/L) require intervention, for example full investigation of exposure. Children are more vulnerable to lead toxicity, as they absorb lead up to 10-fold more effectively than adults. Pregnant women and fetuses are also considered high risk, as are workers exposed lead through their occupations, and families of these workers. Study results:
All individuals tested had lead in their blood, with a geometric mean PbB concentration of 1.34 mcg/dL (0.06 micromol/L). Concentrations were higher in older people, as would be expected, as seniors were likely exposed to higher environmental lead concentrations when they were younger. Among individuals under 20 years of age, at least 95% had PbB levels under 2 mcg/dL. Overall, fewer than 1% of all people tested had blood lead concentrations at or above 10 mcg/dL.
This is a huge improvement over results of the last Canada Health Survey in 1978/79, in which the geometric mean PbB concentration was 4.79 mcg/dL across the same age range, with 27% of these individuals having PbB concentrations at or above 10 mcg/dL.
BPA, on the other hand, is not found in nature. It is used mainly in certain types of plastics, including those for food and water containers, as well as epoxy resins (e.g., linings for canned foods, bottle lids and dental sealants). We are mainly exposed to BPA in our diet, although it is found in water, soil, dust and consumer products. Once ingested, BPA is absorbed quickly and metabolized in the liver to an inactive metabolite with a half-life of under six hours; it is the free BPA that is biologically active. BPA is an endocrine disruptor, and high concentrations adversely affect fertility and development. Threshold concentrations of concern have not been identified.
Nearly 91% of individuals tested had BPA in their urine, which, along with results of US and German studies, suggests that Canadians are exposed to BPA on a continuous basis. The geometric mean concentration was 1.16 mcg/L, with males having higher concentrations overall than females. The reason for the inter-gender difference is not known.
Adults 40 and older had lower urine BPA concentrations as compared with those under 20 years of age; those in the 12-19 year old age group had the highest concentrations. As people are mainly exposed to BPA through diet, this may reflect the increased food consumption in relation to body weight by younger people; differences in absorption/distribution/metabolism/excretion of BPA by this age group; and/or difference in use of BPA-containing products.
Due to BPA’s short half-life and relatively rapid excretion, single urine samples may simply reflect point-in-time concentrations of BPA, not an individual’s average exposure to BPA for any individual.
Bushnik Tetal. Lead and bisphenol A concentrations in the Canadian population. Health Reports, Vol. 21, no. 3, September 2010 • Statistics Canada, Catalogue no. 82-003-XPE. Available at http://www.statcan.gc.ca/pub/82-003-x/2010003/article/11324-eng.pdf
Sanborn MD et al. Identifying and managing adverse environmental health effects: 3. Lead exposure. http://www.cmaj.ca/cgi/reprint/166/10/1287?maxtoshow=&hits=10&RESULTFORMAT=1&title=lead&andorexacttitle=and&andorexacttitleabs=and&andorexactfulltext=and&searchid=1&FIRSTINDEX=20&sortspec=date&fdate=1/1/2000&resourcetype=HWCIT,HWELTR