Article Figures & Tables
Tables
- Table 1:
Blood mercury concentrations in select Canadian surveys of women of child-bearing age and children
Study Design Sampling period Population % with blood Hg concentration above guidance value (8 μg/L) Nunavik Health Survey (16) Representative survey 2004 Inuit women aged 18–39 yr in Nunavik (northern Quebec) 53.3 NCDS (8) Birth cohort 2005–10 Inuit school-aged children in Nunavik 16.9* Canadian Health Measures Survey (17) Representative survey† 2007–09 Women aged 16–49 yr; Canada-wide study 2.2 Geometric mean‡ ± SD or (95% CI) for blood Hg concentration, μg/L NCDS (8) Birth cohort 1995–01 Pregnant Inuit women from Hudson Bay, Nunavik§ 10.4 ± 0.4 Maternal biomonitoring study (18) Convenience sample 2005–07 Pregnant Inuit women in Baffin region 4.0 (3.4–4.7) Pregnant Inuit women in Inuvik 1.1 (0.85–1.5) Pregnant Dene and Metis women in Inuvik 0.70 (0.45–1.1) Canadian Health Measures Survey (17) Representative survey 2007–09 Women aged 16–49 yr; Canada-wide study 0.72 (0.50–0.94) MIREC study (19) Birth cohort 2008–11 Pregnant women in 10 Canadian urban regions 0.86 ± 2.84 Note: CI = confidence interval, Hg = mercury, MIREC = Maternal–Infant Research on Environmental Chemicals study, NCDS = Nunavik Child Development Study, SD = standard deviation.
↵* Not published; proportion calculated directly from the NCDS mercury results.
↵† The study does not obtain samples from Canadians residing on Crown land, in Indian reserves or in remote regions, such as northern Quebec.
↵‡ Distributions of environmental concentrations are often skewed to the right and log-normally distributed. Consequently, many studies use geometric means to estimate central tendency, although this measure may be biased low.
↵§ The contemporary NCDS contains more than 1 birth cohort. These estimates come from one of the cohorts, and the sample comprises pregnant women recruited from the 3 largest communities in the Hudson Bay region of Nunavik.
Specimen Measurement recommended? Exposure period Comments/limitations Blood* Yes Last 3 mo Most common, accurate measure of postnatal methylmercury exposure (10)
Hard to ascertain if there have been acute exposure events that may explain elevated blood level (10)
Possibly affected by hematocrit because mercury binds to hemoglobin (47)
Hair† Yes About 1 mo for every cm of hair Less invasive and sample is easily preserved (10)
Well correlated with blood measurement
Approximate delay of 20 d between exposure and excretion (10)
May be analyzed by cm for a retrospective portrayal of mercury exposure over time (10)
Limited usefulness when hair is short
May be affected by permanent hair treatments, natural hair colour and structure (48)
Fingernail or toenail No Few reference values (10)
Exposure period hard to establish
Limited usefulness in clinical practice
Urine Not for methylmercury May be used to confirm recent exposure to inorganic mercury (10)
Plasma No Very low mercury fraction in plasma (49)
Cord blood at birth Yes Last wk of gestation Considered best available measure of prenatal mercury exposure (10)
Few reference values (10)
Mercury level is about 1.5 higher than in maternal blood at delivery (15)
↵* If patient’s hair is long enough and resources permit, combine with measurement in hair sample (analysis by cm if possible) to clarify whether exposure is long term or acute.
↵† There may be important differences in blood-to-hair mercury ratio between people; singular use of hair sample and of hair-to-blood concentration conversion of 250 proposed by the World Health Organization should be discouraged when establishing individual risk in a clinical setting.
Group Total mercury level Recommended actions In blood In hair Women of child-bearing age
Children < 18 yr
< 8 μg/L (< 40 nmol/L) < 2 μg/g No follow-up required
8–40 μg/L (> 40–200 nmol/L) > 2–10 μg/g Repeat blood/hair test immediately in pregnant women; otherwise repeat in 3–6 mo
Identify dietary sources of exposure and provide dietary advice, taking into account social importance of wild foods
If food insecurity or micronutrient deficiency is a concern, consult with nutritionist or dietitian for low-mercury, high-nutrient food options
> 40–100 μg/L (> 200–500 nmol/L) > 10–25 μg/g Repeat blood/hair test immediately
Identify dietary sources of exposure and provide dietary advice, taking into account social importance of wild foods
If food insecurity or micronutrient deficiency is a concern, consult with nutritionist or dietitian for low-mercury, high-nutrient food options
> 100 μg/L (> 500 nmol/L) > 25 μg/g Repeat blood/hair test immediately
Request mercury speciation in whole blood to discriminate dietary methylmercury from inorganic mercury exposure
If inorganic mercury, identify environmental sources of exposure and seek solutions with patient to eliminate exposure
If methylmercury, identify dietary sources of exposure and provide dietary advice
If accompanied by symptoms of mercury exposure, refer patient to an expert (medical toxicologist or neurologist)
Women > child-bearing age
Men > 18 yr
< 20 μg/L (< 100 nmol/L) < 5 μg/g No follow-up required
20–100 μg/L (100–500 nmol/L) > 5–25 μg/g Repeat blood/hair test in 3–6 mo
Identify dietary sources of exposure and provide dietary advice, taking into account social importance of wild foods
If food insecurity or micronutrient deficiency is a concern, consult with nutritionist or dietitian for low-mercury, high-nutrient food options
> 100 μg/L (> 500 nmol/L) > 25 μg/g Repeat blood/hair test immediately
Request mercury speciation in whole blood to discriminate dietary methylmercury from inorganic mercury exposure
If inorganic mercury, identify environmental sources of exposure and seek solutions with patient to eliminate exposure
If methylmercury, identify dietary sources of exposure and provide dietary advice
If accompanied by symptoms of mercury exposure, refer patient to an expert (medical toxicologist or neurologist)
All groups (Quebec only)
≥ 12 μg/L (≥ 60 nmol/L) ≥ 3 μg/g Test result must be declared to regional public health authority (consult steps to be taken at www.msss.gouv.qc.ca/professionnels/mado/demarche_medecins.php)