Identification of chemical mixtures to which Canadian pregnant women are exposed: The MIREC Study (Lay summary)

Lee WC, Fisher M, Davis K, Arbuckle TE, Sinha SK. Environment International 2017 Feb;99:321-330. doi: 10.1016/j.envint.2016.12.015.

Prenatal exposure to elevated levels of some environmental chemicals may be associated with adverse effects during pregnancy and fetal development, or during childhood. Generally research studies have looked at associations between one specific chemical at a time and potential adverse effects on pregnancy and infant health.  However, in the real world, we are exposed to multiple chemicals at the same time.  Therefore, it is important to know which chemicals pregnant women are exposed to at one point in time and to try to identify who tends to be more exposed to certain groups (mixtures) of chemicals than others.

Using data on 1,744 women from the MIREC Study, this study looked for any patterns in the chemicals to which the women were exposed. A wide range of chemicals were considered in this study including metals (arsenic, lead, mercury, cadmium, manganese), polychlorinated biphenyls (PCBs), organochlorine and organophosphate pesticides, perfluoroalkyl substances, bisphenol A (BPA), and phthalate metabolites. These chemicals were measured in maternal blood and urine collected during the 1st trimester of pregnancy. Additionally, data were collected on various maternal factors (age, education, household income, number of children, pre-pregnancy body mass index (BMI), country of birth and smoking status).

Various statistical methods were used to identify which chemicals tend to occur together (a chemical mixture) in maternal blood or urine and to describe the women with higher exposure to specific chemical mixtures.  One of the mixtures of chemicals identified was persistent organic pollutants (PCBs and organochlorine pesticides).  Women having lower education, higher annual household income, being born in Canada, being overweight prior to pregnancy, or who were expecting their first child tended to have higher blood concentrations of the chemicals in this mixture. Human exposure to persistent organic pollutants mostly comes from diet, particularly meat and dairy consumption. On the other hand, a second chemical mixture consisting of some phthalates (which were found in 98% of all women), was not associated with any particular maternal characteristics. Phthalates are often used in food packaging, building and furniture materials, and medical devices, as well in cosmetics and personal care products.

This research study provides some indication of the characteristics of women exposed to mixtures of common chemicals. This type of analysis could be used in future studies to investigate the health effects of chemical mixtures in pregnant women and their children.