26. Concentrations of persistent organic pollutants in maternal and cord blood from the maternal-infant research on environmental chemicals (MIREC) cohort study (lay summary)

Fisher M, Arbuckle TE, Liang CL, LeBlanc A, Gaudreau E, Foster WG, Haines D, Davis K, Fraser WD. Environmental Health. 2016 May 4;15(1):59. doi: 10.1186/s12940-016-0143-y

The Canadian population, including pregnant women and their developing fetuses, can be exposed to very small amounts of persistent organic pollutants (POPs), such as organochlorine pesticides (OCs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and perfluoroalkyl substances (PFASs). POPs are man-made chemicals (many of which have been banned or their use restricted in Canada) that tend to remain in the environment and be stored in fatty tissues of humans and animals. Diet and house dust (for PBDEs) can be sources of exposure to POPs.

While data are available for the general population in Canada (https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/environmental-contaminants/report-human-biomonitoring-environmental-chemicals-canada-health-canada-2010.html) on their exposure to these chemicals, similar data for pregnant women and their infants do not exist. Analysing blood collected from the MIREC women during pregnancy and from umbilical cord blood at delivery provides an opportunity to obtain a snapshot of exposure for these two susceptible populations. Levels of several POPs were measured in maternal and cord blood samples from nearly 2,000 participants in the MIREC Study. The women were recruited from 10 cities across Canada between 2008 and 2011. Information on factors that may be associated with higher or lower levels of POPs in maternal blood was collected in the questionnaires administered to the women during pregnancy.

The study found that while POPs were frequently detected at very low levels in maternal blood, most of these chemicals were not detected in umbilical cord blood. The PFASs were the chemicals most frequently detected in both maternal and cord blood. PFASs are used in a wide variety of products including stain/water/oil-repellent fabric protectors, in water/oil-repellent paper coatings, wiper blades, bike chain lubricant, wire and cable insulation, pharmaceutical packaging, food packaging, engine oil additives, nail polish, hair-curling and straightening products, metal plating and cleaning, fire retardant foams, inks, and varnishes. Similar to what has been reported in other studies, parity (the number of previous live births the woman has had), maternal age, household income, education, smoking status, pre-pregnancy BMI (body mass index = a person’s weight in kilograms divided by her height in meters squared), country of birth and fish consumption were significant predictors for most chemicals. For example, as the number of births the woman has had (parity) increased, the levels of most POPs in her blood decreased. Often, as household income increased, blood concentrations of POPs also increased. Women born outside Canada tended to have significantly higher levels of OCs, PBDEs and PCBs, but lower levels of some PFASs. Compared to studies of pregnant women in other countries or women of reproductive age in Canada, blood levels of these POPs in MIREC participants were similar or in many cases lower.

In conclusion, while a number of POPs were measured in the blood of pregnant women in MIREC, their levels were very low. In addition, with the exception of PFASs, which were present but at much lower levels than in maternal blood, POPs were rarely detected in cord blood, suggesting that the fetus received limited exposure to these chemicals during pregnancy.