Maternal-Infant Research on Environmental Chemicals (The MIREC Study)
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, human milk 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 biomonitoring reports provide much needed national data on exposure of the Canadian population to several important environmental contaminants; however, this survey is not collecting 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 human milk is limited. There have also been few national studies that have specifically measured the nutrients and immuno-protective factors that are found in human 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 the study known as the Maternal-Infant Research on Environmental Chemicals (MIREC).
Description of the MIREC Study
MIREC is a national-level multi-year research study that has recruited close to 2,000 women from the following cities: Vancouver, Edmonton, Winnipeg, Sudbury, Ottawa, Kingston, Hamilton, Toronto, Montreal and Halifax. Women were recruited during the first trimester of pregnancy and followed through pregnancy and up to ten weeks after birth. Participants had to 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:
- To measure the extent to which pregnant women and their babies are exposed to environmental chemicals, as well as tobacco smoke;
- To assess what health risks, if any, are associated with exposure to elevated levels of environmental chemicals;
- To measure the levels of environmental chemicals and some of the beneficial components (nutritional and immune constituents) of human milk;
- To collect small amounts of biological fluids from consenting participants to store in the MIREC Biobank for further research on fetal growth, pregnancy, and health of mother and child.
Biological markers of environmental chemicals and tobacco smoke exposure are being measured in the mothers' blood, urine, hair, and human milk and in their babies' umbilical cord blood and meconium (which is the baby's first stool). Nutrient components of human milk are also being studied. These include vitamin D, macro nutrients (calcium, magnesium, potassium, sodium, and phosphorus), folic acids, fatty acids, and immunoprotective constituents.
Mothers were also asked to complete questionnaires throughout their pregnancy and after birth.
Some of the children are being followed as they grow to measure:
- Various indicators of infant health at birth and six months of age;
- Child behavior at 3 years of age;
- Child growth, behavior, and language and communication skills at up to 5 years of age;
- Exposure to metals such as lead and mercury.
The MIREC study is a collaborative effort among Health Canada scientists, the Sainte-Justine Hospital in Montreal, and clinical and academic researchers. Sainte-Justine Hospital in Montreal is the coordinating centre for the study. Laboratories at the Centre de Toxicologie du Québec and Health Canada are conducting 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 human 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 three and 79 years.
The MIREC study will measure 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;
- perchlorate, a naturally occurring and man-made chemical used in rocket fuel, fireworks, flares and explosives;
- ochratoxin A, a naturally occurring fungal toxin;
- 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.
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.
Study Findings and Publications to Date
Cohort Profile: The Maternal-Infant Research on Environmental Chemicals (MIREC) Research Platform
The Maternal-Infant Research on Environmental Chemicals (MIREC) Study was established to obtain national biomonitoring data for pregnant women and their infants and to examine potential adverse health effects of prenatal exposure to environmental chemicals on pregnancy and infant health. Biomonitoring is the measurement of a chemical substance (or break-down products of that substance) in human tissues or fluids. Measurements are usually taken in blood and urine, and sometimes in hair, saliva, or human milk. In this study Health Canada researchers participated in the recruitment and analysis of samples from approximately 2000 women during their first trimester of pregnancy from 10 sites across Canada and followed through to delivery. Questionnaires administered during pregnancy and post-delivery collected information on occupation, lifestyle, medical history, environmental exposures and diet. Information on the pregnancy and the infant were collected from medical charts. Maternal blood, urine, hair and milk as well as cord blood and infant meconium were collected and analysed for several environmental chemicals and nutrients. Additional samples were stored in the study's biobank.
MIREC participants tended to smoke less, be older and have a higher education level than national averages. The MIREC study, while smaller in number of participants than several international studies, has one of the most extensive datasets on prenatal exposure to multiple environmental chemicals in the world. The data, samples collected, and follow-up studies will make the MIREC research platform a significant resource for examining potential adverse health effects of prenatal exposure to environmental chemicals. Additionally, Health Canada will use the results of this study to inform future risk assessments and risk management of environmental chemicals, especially regarding exposures during pregnancy. Results of this research are published in the journal Paediatric and Perinatal Epidemiology (2013 Jul;27(4):415-25).
Phthalate and Bisphenol A Exposure among Pregnant Women in Canada
Health Canada collects population biomonitoring data in order to obtain direct estimates of chemical exposures that help to inform sound decision-making about health risks to Canadians. Bisphenol A (BPA) and phthalates are two groups of chemicals commonly measured in urine in population surveys; however, Canadian data for pregnant women are limited. These chemicals were measured in first trimester urine samples from approximately 2,000 Canadian women in the Maternal-Infant Research on Environmental Chemicals (MIREC) Study. Approximately 90% of the women had detectable levels of BPA. An analysis of urinary concentrations of BPA by maternal characteristics showed that concentrations: (1) decreased with increasing maternal age, (2) were higher in current smokers or women who quit during pregnancy compared to never smokers, and (3) tended to be higher in women who provided a fasting urine sample, were born in Canada, and had lower incomes and education. Some phthalates were commonly found in maternal urine and others were rarely found. This study provides the first biomonitoring results for a large population of pregnant women sampled in the first trimester of pregnancy. The results indicate that exposure amongst this population of pregnant women to these chemicals is comparable to, and in some cases lower than, that observed in a national survey of women of reproductive age in Canada - the Canadian Health Measures Survey. These results on human exposure levels will be used to inform risk assessment and risk management activities related to these chemicals. This research is published in the journal Environment International (2014 Jul 68:55-65).
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