Maternal-Infant Research on Environmental Chemicals (The MIREC Study)

The Issue

Recent reports have raised concerns about the number of chemicals in our bodies and the health effects, if any, which may be associated with the levels measured. Reliable data on the levels of environmental chemicals of concern in Canadians are limited. Major technological advances in the analysis of chemicals mean that extremely low levels can now be detected in body fluids, tissues and hair. Therefore it is not unusual to find very small levels of chemicals in the urine or blood of participants given that we come across many of these chemicals in our everyday life. It is well known that high levels of some chemicals, such as lead and mercury, do cause health effects. What is not always clear is whether there are any measurable health effects from lower levels of exposure. The Canadian Health Measures Survey (2007-09) is expected to provide much needed national data on exposure of the Canadian population to several important environmental contaminants; however, this survey will not collect data for two of the most susceptible and vulnerable populations: the pregnant woman and her baby.

As awareness of the presence of environmental chemicals in humans is increasing, Canada as well as other countries, are studying pregnant women in order to better understand their exposure to these chemicals. Although breast feeding is known to be the best method for feeding infants, recent Canadian information on environmental chemicals found in breast milk is limited. There have also been few national studies that have specifically measured the nutrients and immuno-protective factors that are found in breast milk.

Smoking in pregnancy has long been linked with a higher risk of low birth weight, and other harmful effects on the baby. Currently, there is little Canadian information about the extent to which women are exposed to tobacco smoke during pregnancy. As well, there is limited information on whether smoking behaviour changes during pregnancy.

Given these data gaps, scientists at Health Canada and their academic and clinical research collaborators have designed and are now carrying out the study known as the Maternal-Infant Research on Environmental Chemicals (MIREC).

Description of the MIREC Study

MIREC is a national five-year research study that is recruiting about 2,000 women from the following cities: Vancouver, Edmonton, Winnipeg, Sudbury, Ottawa, Kingston, Hamilton, Toronto, Montreal and Halifax. Women will be recruited during the first trimester of pregnancy and followed through pregnancy and up to eight weeks after birth. Participants must be 18 years of age or older and six to 13 weeks pregnant to be eligible for the study. The main goals of this study are:

1. to measure the extent to which pregnant women and their babies are exposed to environmental chemicals, as well as tobacco smoke;
2. To assess what pregnancy health risks, if any, are associated with exposure to heavy metals (lead, mercury, cadmium, arsenic and manganese);
3. To measure the levels of environmental chemicals and some of the beneficial components (nutritional and immune constituents) of breast milk.

Biological markers of environmental chemicals and tobacco smoke exposure will be measured in the mothers' blood, urine, hair, and breast milk and in their babies' umbilical cord blood and meconium (which is the baby's first stool). Mothers will also be asked to complete questionnaires throughout their pregnancy and after birth.

The MIREC study is a collaborative effort among Health Canada scientists, the Sainte-Justine Hospital in Montreal, and clinical researchers from the other participating cities. Sainte-Justine Hospital in Montreal is the coordinating centre for the study. Laboratories at the Centre de Toxicologie du Québec and Health Canada will conduct the analysis of tissues and fluids.

MIREC and Biomonitoring

Biomonitoring is the measurement of a chemical substance (or the breakdown products of that substance) in human tissues or fluids. Measurements are usually taken in blood and urine, and sometimes in hair, saliva or breast milk. Biomonitoring studies that focus on sub-populations such as pregnant women can help us compare levels of exposure for a particular group to the broader population. The MIREC study complements the Canadian Health Measures Survey, launched in early 2007 by Statistics Canada, which is collecting biological samples and information on health, lifestyle and environmental chemicals from 5,000 Canadians between the ages of six and 79 years.

The MIREC study will measure heavy metals such as lead, mercury, arsenic, manganese and cadmium, as well as other chemicals including:

• phthalates and bisphenol A, which are used to make plastics and vinyl;
• PBDEs (polybrominated diphenyl ethers), which are added to products to make them less likely to catch fire;
• organochlorine pesticides, which are no longer registered for use in Canada, but continue to persist in the environment.
• organophosphate (OP) pesticides, most of which are used in agriculture for insect control and usually do not persist in the environment; the OP pesticides have been subject to a recent science-based and rigorous re-evaluation by Health Canada;
• PCBs (polychlorinated biphenyls), formerly used as an ingredient in many industrial materials;
• cotinine, which is a by-product of smoking; and
• perfluorinated compounds, which are used in the manufacture of grease and water repellents used on products.

Health Canada's Role

The MIREC study is a key deliverable under the Government of Canada's Chemicals Management Plan. Launched in December 2006, the Plan is a significant step forward in reducing the impact of environmental chemicals on human health and the environment.

MIREC is co-funded by Health Canada, the  Canadian Institutes of Health Research (CIHR) and the  Ontario Ministry of the Environment.

Public Health Relevance

The MIREC study will generate new knowledge on Canadians' exposure to environmental chemicals. This information will help to strengthen health risk assessments and support measures to reduce the release of contaminants into the environment and to limit Canadians' exposure.

Contact Information

The MIREC study coordinating centre is located at the Sainte-Justine in Montreal. For further information please refer to your regional contact listed at www.mirec-canada.ca.

Related Resources

• Frequently Asked Questions - MIREC Study

For more information about chemical substances found in the environment please visit:

•  The Government of Canada's Chemicals Substances Website
• First Nations and Inuit Health - Healthy Pregnancies and Babies
• Healthy Babies
• HealthlyCanadians.gc.ca - Healthy Pregnancy
• Healthy Pregnancy
•  Canadian Health Network's Healthy Pregnancy Page
• It's Your Health - Effects of Lead on Human Health
• It's Your Health - Mercury and Human Health
• It's Your Health - PBDE Flame Retardants and Human Health
• It's Your Health - Second-hand Smoke
• It's Your Health - PCBs
• It's Your Health - Arsenic in Drinking Water
• Vulnerable Populations