Maternal and umbilical cord blood levels of mercury, lead, cadmium, and essential trace elements in Arctic Canada

Abstract

Maternal and umbilical cord blood levels of mercury (Hg), lead (Pb), cadmium (Cd), and the trace elements copper (Cu), zinc (Zn), and selenium (Se) are reported for Inuit, Dene/Métis, Caucasian, and Other nonaboriginal participants from Arctic Canada. This is the first human tissue monitoring program covering the entire Northwest Territories and Nunavut for multiple contaminants and establishes a baseline upon which future comparisons can be made. Results for chlorinated organic pesticides and PCBs for these participants have been reported elsewhere. Between May 1994 and June 1999, 523 women volunteered to participate by giving their written informed consent, resulting in the collection of 386 maternal blood samples, 407 cord samples, and 351 cord:maternal paired samples. Geometric mean (GM) maternal total mercury (THg) concentrations ranged from 0.87 μg/L (SD=1.95) in the Caucasian group of participants ( n = 1 3 4 ) to 3.51 μg/L (SD=8.30) in the Inuit group ( n = 1 4 6 ). The GM of the Inuit group was 2.6-fold higher than that of the Dene/Métis group (1.35 μg/L, SD=1.60, n = 9 2 ) and significantly higher than those of all other groups ( P<0.0001). Of Inuit women participants, 3% ( n = 4 ) were within Health Canada's level of concern range (20–99 μg/L) for methylmercury (MeHg) exposure. Of Inuit and Dene/Métis cord samples, 56% ( n = 9 5 ) and 5% ( n = 4 ), respectively, exceeded 5.8 μg/L MeHg, the revised US Environmental Protection Agency lower benchmark dose. GM maternal Pb was significantly higher in Dene/Métis (30.9 μg/L or 3.1 μg/dL; SD=29.1 μg/L) and Inuit (31.6 μg/L, SD=38.3) participants compared with the Caucasian group (20.6 μg/L, SD=17.9) ( P<0.0001). Half of all participants were smokers. GM blood Cd in moderate smokers (1–8 cigarettes/day) and in heavy smokers (>8 cigarettes/day) was 7.4-fold higher and 12.5-fold higher, respectively, than in nonsmokers. The high percentage of smokers among Inuit (77%) and Dene/Métis (48%) participants highlights the need for ongoing public health action directed at tobacco prevention, reduction, and cessation for women of reproductive age. Pb and THg were detected in more than 95% of all cord blood samples, with GMs of 21 μg/L and 2.7 μg/L, respectively, and Cd was detected in 26% of all cord samples, with a GM of 0.08 μg/L. Cord:maternal ratios from paired samples ranged from 0.44 to 4.5 for THg, from 0.5 to 10.3 for MeHg, and 0.1 to 9.0 for Pb. On average, levels of THg, MeHg, and Zn were significantly higher in cord blood than in maternal blood ( P<0.0001), whereas maternal Cd, Pb, Se, and Cu levels were significantly higher than those in cord blood ( P<0.0001). There was no significant relationship between methylmercury and selenium for the range of MeHg exposures in this study. Ongoing monitoring of populations at risk and traditional food species, as well as continued international efforts to reduce anthropogenic sources of mercury, are recommended.