Maternal-Infant Research on Environmental Chemicals (The MIREC Research Platform)
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 focused on 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 and potential health effects, if any, on maternal, infant and child health.
Breast feeding is the best method for feeding infants; however, there have been few national studies that have specifically measured the nutrients and immuno-protective factors that are found in human milk. Also recent Canadian information on environmental chemicals found in human milk is limited.
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 behavior changes during pregnancy.
Given these data gaps, scientists at Health Canada and their academic and clinical research collaborators designed the Maternal-Infant Research on Environmental Chemicals (MIREC) Research Platform which comprises the MIREC Study, and the follow-up studies MIREC-ID, MIREC-CD3, MIREC-CD Plus and MIREC-ENDO, as well as several MIREC Biobank projects. Data collection has been completed for all the studies except for MIREC-ENDO and some of the Biobank projects.
Description of the MIREC Study and the MIREC Research Platform
The MIREC Study 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, vitamins and minerals (folate (vitamin B9), calcium, magnesium, potassium, sodium, and phosphorus), 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 and development at birth and six months of age (MIREC-ID);
- Child behavior at 3 years of age (MIREC-CD3);
- Child growth, behavior, and language and communication skills up to 5 years of age and blood or urine concentrations of some chemicals in the younger children (MIREC-CD Plus);
- Child growth and pubertal development from middle childhood through the early teenage years (MIREC-ENDO)
- Exposure to metals such as lead and mercury and other persistent chemicals (MIREC-ENDO).
The MIREC Research Platform 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.
The MIREC-ID (Infant Development) Study
In MIREC-ID, approximately 500 families from the MIREC Study were invited to participate in a follow-up study. The aims of MIREC-ID are to:
- To examine the potential associations between prenatal exposure to various environmental chemicals and
- infant size at birth and at 6 months of age,
- early markers of sexual development in newborns because some environmental chemicals are thought to disrupt hormones,
- infant sensory development,
- infant behaviors.
- To identify factors that may modify the infant's vulnerability to environmental chemicals, such as breastfeeding, socio-economic factors and maternal characteristics.
The MIREC-CD3 (Child Development at 3 years) and MIREC-CD Plus (Early Childhood Biomonitoring and Neurodevelopment) Studies
Up to 800 MIREC families participated in various segments of the MIREC-CD3 and MIREC-CD Plus Studies. The specific aims of these studies are to:
- Study the potential associations between prenatal exposures to various environmental chemicals and child neurodevelopment at around 3 years of age, including cognitive, language and behavioural tests.
- Measure child's growth and physical development and examine potential associations with prenatal environmental chemical exposures.
- Analyse the blood and urine of the younger children for various environmental chemicals (e.g., metals, phthalates and bisphenol A).
The MIREC-ENDO (Pubertal Timing, Endocrine and Metabolic Function) Study
The goal is to recruit approximately 1000 MIREC families to participate in MIREC-ENDO. The aims of this study are:
- To study whether prenatal exposure to elevated levels of various environmental chemicals, as well as other prenatal factors (e.g. gestational diabetes), are related to the onset and progression of puberty, and changes in metabolism and growth in children.
- To explore the effect of maternal health problems and exposure to environmental chemicals during the MIREC pregnancy on long-term maternal health (e.g. blood pressure, blood sugar).
- To measure exposure to various emerging environmental chemicals (not previously measured in MIREC) in stored maternal urine samples.
- To measure current exposure to more persistent environmental chemicals in MIREC children.
The MIREC Biobank
The MIREC Biobank is a repository for biospecimens (e.g. blood, urine, human milk) and data collected from MIREC participants with their consent. These biospecimens and the associated data are coded and safely stored for use in future research studies such as measuring exposure to new priority environmental chemicals and identifying early markers of clinical disease, nutritional status and genetic susceptibility, with the ultimate goal of improving the health of pregnant women and children in Canada. Policies and procedures have been put in place to oversee the proper use of the Biobank, which resides at the Sainte-Justine's Hospital Research Center in Montreal. Researchers have applied to access these data and biospecimens for Biobank projects such as studies of air pollution and newborn size, infant immune markers, and measuring new chemicals such as triclosan in maternal urine.
MIREC and Biomonitoring
Biomonitoring is the measurement of a chemical substance (or the breakdown products of that substance) in human tissues or fluids (biospecimens). 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 ongoing 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 Canadians between the ages of three and 79 years of age.
The MIREC Study measured metals such as lead, mercury, arsenic, manganese and cadmium, as well as other chemicals including:
- phthalates and bisphenol A (BPA), 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;
- Triclosan, a chemical used as a preservative as well as to kill or remove bacteria in various products, such as soaps, toothpaste and skin cleaners;
- cotinine, which is a by-product of smoking; and
- perfluoroalkyl substances, which are used in the manufacture of grease and water repellents used on products.
Health Canada's Role
The MIREC Research Platform 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.
The MIREC Study was co-funded by Health Canada, the Canadian Institutes of Health Research (CIHR) and the Ontario Ministry of the Environment. The MIREC follow-up studies have been funded by Health Canada's Chemicals Management Plan.
Public Health Relevance
The MIREC Research Platform will generate new knowledge on Canadians' exposure to environmental chemicals and potential risk factors associated with maternal and child health. 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.
Some Study Findings and Publications
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).
Exposure to Free and Conjugated Forms of Bisphenol A and Triclosan among Pregnant Women in the MIREC Cohort
Health Canada has the responsibility to assess the health risks to Canadians associated with exposure to chemicals in the environment. The Maternal-Infant Research on Environmental Chemicals (MIREC) study was designed to measure exposure to and any potential health effects of elevated levels of environmental chemicals during pregnancy. Two of the chemicals for which there are limited data on levels in pregnant women are triclosan and bisphenol A (BPA). Triclosan is used as an antimicrobial in a wide range of cosmetics and personal care products, including non-prescription drugs. BPA is used to make a hard, clear plastic and may also be found in epoxy resin linings on the inside of metal-based food and beverage cans. Thermal papers such as receipts and tickets may also be a source of BPA. In this study, Health Canada undertook to measure these two chemicals in a urine sample from approximately 1,900 pregnant women participating in the MIREC Study. BPA levels were higher in women with a lower household income, under 25 years of age or in smokers. Triclosan levels tended to be higher in women who had never smoked or were 25 years of age or older. Health Canada will use the results of this study to estimate exposure to these chemicals for the Canadian population. The results of this study are published in the journal Environmental Health Perspectives, (2015 Apr;123(4):277-84).
Maternal Blood Metal levels and Fetal Markers of Metabolic Function
Health Canada helps to protect the health of Canadians by assessing and managing the health risks associated with exposure to environmental contaminants. This study was done in partnership with scientists at Dalhousie University and aimed to investigate the potential adverse effects of prenatal exposure to metals on fetal growth using data from the Maternal-Infant Research on Chemicals (MIREC) Study. The fetal time period is a window of enhanced susceptibility to the potential adverse effects of environmental contaminants. Previous research has suggested that maternal exposure to metals commonly found in the environment may adversely affect fetal growth. Examination of fetal markers of metabolic function provides a means for assessing the susceptibility of fetal development to environmental contaminant exposures. This research examined the relationship between prenatal exposure to four metals (lead, mercury, arsenic, and cadmium) and biomarkers of metabolic function in umbilical cord blood. Individuals may be exposed to these metals through contaminated food or water, industrial emissions or cigarette smoking. Leptin and adiponectin are hormones whose levels may be predictive of childhood growth patterns. Umbilical cord blood levels of these hormones served as biomarkers of metabolic function in this study. It was observed that cord blood leptin levels were higher among female infants than male infants, while cord blood adiponectin levels were approximately the same among males and females. It was also observed that, compared to women with low exposure levels, women with high levels of exposure to cadmium were more likely to have infants with high cord blood leptin levels. This association was, however, only observed among male infants. No significant associations were observed between the other metals and these biomarkers of metabolic function. The study results suggest that prenatal exposure to some metals may have an impact on fetal metabolic development, which provides motivation to further examine the role of prenatal exposures to contaminants, such as cadmium, on childhood growth patterns in order to develop a more complete picture of their potential impact on child health and growth. This study was published in the journal Environmental Research, (2015 Jan;136:27-34).
A Birth Cohort Study to Investigate the Association between Prenatal Phthalate and Bisphenol A Exposures and Fetal Markers of Metabolic Dysfunction
Phthalates and bisphenol A (BPA) are chemicals that are used in a variety of plastic consumer products. Because these chemicals are structurally similar to the hormones that our bodies produce, these chemicals may have harmful effects on the endocrine and reproductive systems. This is of particular concern for pregnant women and their developing babies because gestation is a time of enhanced susceptibility to the potential adverse effects of environmental contaminants. Scientific research has recently been examining the role of common environmental contaminants that impact metabolism, through effects on the endocrine system, as possible contributing factors in the rise in the number of individuals that exceed a healthy weight and that have type-2 diabetes. In particular, this study examined the relationship between pregnant mother's exposure to phthalates and bisphenol A, as measured through levels in their urine, and biomarkers of metabolic function in umbilical cord blood obtained through the Maternal-Infant Research on Environmental Chemicals (MIREC) biobank. The two biomarkers, leptin and adiponectin, are hormones that may provide an indication of childhood growth patterns. The results showed that leptin levels were higher among female infants than male infants, while adiponectin levels were approximately the same among males and females. When compared to women with low exposure levels, women with moderate levels of exposure to one phthalate metabolite, monobenzyl phthalate, were slightly more likely to have high cord blood leptin levels. As well, women with high exposure to the phthalate metabolite, monoethyl phthalate, were slightly more likely to have high cord blood adiponectin levels. This research suggests that exposures to common environmental contaminants during pregnancy may have an impact on fetal hormone levels associated with metabolic function. Further research needs to be done to examine whether these changes in hormone levels are associated with changes in childhood growth trajectories leading to obesity and/or type-2 diabetes. This work was led by researchers at Dalhousie University and funded by the Canadian Diabetes Association (CDA). Health Canada scientists are the lead on the MIREC Study, assisted with the interpretation of these results, provided editorial advice and are co-investigators on the grant to Dalhousie University scientists from the CDA. This study was published in the journal Environmental Health (2014 Oct 22;13:84).
Maternal Exposure to Perfluorinated Chemicals and Reduced Fecundity: the MIREC Study.
Health Canada helps to protect the health of Canadians by assessing and managing the health risks associated with exposure to environmental contaminants. In support of these efforts, the Maternal-Infant Research on Environmental Chemicals (MIREC) Study was established to examine the potential adverse health effects of exposure to environmental chemicals, such as perfluorinated chemicals (PFCs), on pregnancy and infant health in Canada. PFCs have been widely used in domestic and industrial products, but have been largely phased out in the last decade through risk management efforts. Although the production of several PFCs has declined, recent national biomonitoring surveys in Canada (https://www.canada.ca/en/health-canada/services/environmental-workplace-health/environmental-contaminants/human-biomonitoring-environmental-chemicals/canadian-health-measures-survey.html) have shown that nearly all participants had low levels of PFCs in their blood. Some PFCs have been linked to adverse health effects, especially in animal models. There is conflicting evidence about the effects of PFCs on human fertility. Although some recent studies suggest that increasing concentrations of PFCs may increase the time it takes to get pregnant, other studies reported no effect. This study examined the association between PFCs and time to pregnancy using the MIREC Study population. During the first study visit (around 12 weeks of pregnancy), women were asked how many months of unprotected intercourse it took them to become pregnant with their current pregnancy. Infertility was defined as more than 12 months of trying to get pregnant or infertility treatment for the current pregnancy. Maternal blood samples were analysed for three of the most common PFCs: perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), and perfluorohexane sulfonate (PFHxS)). A total of 1743 women were included in the analyses. The results were adjusted for potential confounding factors such as age, socio-economic status, and body mass index. The study found that levels of PFCs were lower than those reported in previous studies. Even at these lower levels, however, it was found that PFOA and PFHxS were associated with an increase in the number of months to become pregnant, while no significant association was observed for PFOS. In addition, the odds of infertility increased as blood PFOA or PFHxS concentrations increased, while no significant association was observed for PFOS. These results suggest that exposure to PFOA and PFHxS, even at lower levels than previously reported, may impact fertility. Although this is the largest study to date that has measured the association between exposure to PFCs and the time it took to conceive, these results need to be interpreted with caution. Important factors contributing to couple fertility were not measured, including the health status and exposures of the male partners. Nevertheless, these results support measures taken to reduce the release of these contaminants into the environment in order to limit Canadians' exposure. This study was conducted in collaboration with scientists from the Sainte-Justine University Hospital Research Centre, University of Montreal. This study was published in the journal Human Reproduction (2015 Mar;30(3):701-9).
Prenatal Exposure to Phthalates, Bisphenol A and Perfluoroalkyl Substances and Cord Blood levels of IgE, TSLP and IL-33.
Health Canada collects population biomonitoring data on exposure to environmental chemicals to inform sound decision-making about health risks to Canadians. It is known that rates of childhood allergies and asthma have been increasing in recent decades, but this trend is not completely explained by established risk factors such as family history and smoking. It has been hypothesized that exposure to certain environmental contaminants, such as phthalates, bisphenol A, and perfluorinated compounds, may increase the risk of childhood allergic disease. Prenatal exposure to these contaminants is of particular interest as the fetal period is a critical window of immune system development. Disruptions to fetal immune system development, as evidenced by changes in levels of immune system biomarkers, may increase the risk of future childhood allergic disease. In this study, researchers at Dalhousie University, in collaboration with Health Canada, examined the relationship between prenatal exposure to bisphenol A (BPA), phthalates and perfluorinated compounds, and umbilical cord blood levels of three different immune system biomarkers. Data from the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, a national study of approximately 2,000 pregnant women, were used to explore this relationship. Of these women, 1,258 had a singleton, term birth and provided a cord blood sample. Within this population, it was found that maternal levels of phthalates, BPA, and perfluorinated compounds were not associated with immunotoxic effects that manifest as elevated levels of cord blood immune system biomarkers. These results add to the body of scientific knowledge, which informs risk assessment and risk management decisions at Health Canada for these chemicals. This work was led by scientists at Dalhousie University and was published in the journal Environmental Research (2015 Jul;140:360-8).
Exposure to Phthalates, Bisphenol A and Metals in Pregnancy and the Association with Impaired Glucose Tolerance and Gestational Diabetes Mellitus: The MIREC Study
Health Canada helps to protect the health of Canadians by assessing and managing the potential health risks associated with exposure to environmental contaminants. In support of these efforts, the Maternal-Infant Research on Environmental Chemicals (MIREC) Study was established to examine the potential adverse health effects of exposure to environmental chemicals during pregnancy. In this study led by scientists at the IWK Health Centre in Halifax, chemicals that may interfere with the hormone system were measured to see if they increased the risk of developing gestational diabetes. Four metals (lead, cadmium, mercury and arsenic) were measured in the women's blood samples, while BPA and several phthalates, which are chemicals used in some plastics, were measured in their urine. Results of a glucose tolerance test administered during the pregnancy were used to identify those women with gestational diabetes or with impaired glucose tolerance, which is a less severe glucose disorder. It was found that women with the highest levels of arsenic in their blood were about 4 times as likely to have gestational diabetes as women with the lowest levels of arsenic. Women with the highest levels of the other metals, phthalates or bisphenol A did not have a higher risk of gestational diabetes or impaired glucose tolerance. The results of this work add to the body of evidence supporting a potential role for arsenic in the development of diabetes. These results will contribute to Health Canada's efforts to manage the risks of these chemicals. This study was published in the journal Environment International (2015 Oct;83:63-71).
Concentrations of Persistent Organic Pollutants in Maternal and Cord Blood from the Maternal-Infant Research on Environmental Chemicals (MIREC) Cohort Study.
Health Canada is responsible for the assessment and management of health risks, including those associated with exposure to chemicals in the environment. Persistent organic pollutants, or POPs, are chemicals that tend to linger in the environment and accumulate in fatty tissues of humans and animals. Exposure to some of these chemicals has been linked with specific health effects. Pregnant women are an especially important population to monitor for environmental exposures, given the vulnerability of the developing fetus. In this study, the levels of several POPs were measured in first trimester maternal blood and umbilical cord blood samples from the Maternal-Infant Research on Environmental Chemicals (MIREC) cohort. Women in the MIREC Study were found to be exposed to several chemicals, many of which were banned from use in Canada several years ago. However, the study found that, compared to other population studies, the MIREC participants had lower contaminant concentrations. In addition, parity, maternal age, income, education, smoking status, pre-pregnancy body mass index (BMI), and whether or not one was born in Canada were found to have an impact on contaminant levels. The results of this study will help to inform Health Canada risk assessment and risk management activities as well as public health measures aimed at protecting this vulnerable population from the potential effects, if any, of exposure to environmental chemicals. This work was published in the journal Environmental Health (2016 May 4;15(1):59).
Determinants of Urinary Concentrations of Dialkyl Phosphates among Pregnant Women in Canada - Results from the MIREC Study
Health Canada helps to protect the health of Canadians by assessing and managing the health risks associated with exposure to environmental contaminants. Organophosphates (OPs) are a group of closely related pesticides used extensively in agricultural and non-agricultural sites that have potential to affect functioning of the nervous system. Exposure to elevated levels of OPs during pregnancy has been associated with adverse birth outcomes and poorer neurodevelopment in children. Several of these pesticides have been voluntarily discontinued or have had their residential uses severely restricted. The Maternal-Infant Research on Environmental Chemicals (MIREC) Study was established to obtain national-level biomonitoring data for pregnant women and their infants over a three-year period from 2008 to 2011 in 10 Canadian cities. The objective of the present study was to examine the relationship between levels of OP pesticide metabolites in maternal urine and various factors that are potential sources of exposure or determinants of levels. Six OP metabolites were measured in 1st trimester urine samples of 1884 pregnant women from the MIREC Study. The following characteristics were significantly associated with higher urinary concentrations: higher education, first pregnancy, normal pre-pregnancy body mass index, non-smoker, fasting prior to urine collection, winter season at urine collection, and early and late day urine collection times. Dietary items significantly related with higher concentrations included higher intake of citrus fruits, apple juice, sweet peppers, tomatoes, beans and dry peas, soy and rice beverages, whole grain bread, white wine, green and herbal tea. In conclusion, factors and potential sources of exposure to OP pesticides were identified and may be useful to Health Canada's Pest Management Regulatory Agency in their re-evaluation of these pesticides and their uses. This study was conducted in collaboration with scientists from the University of Montreal and was published in the journal Environment International (2016 Sep;94:133-140).
Maternal and Fetal Exposure to Cadmium, Lead, Manganese and Mercury: The MIREC Study
Health Canada helps to protect the health of Canadians by assessing and managing the health risks associated with exposure to environmental contaminants. Limited information is available on levels of potentially harmful environmental metals in pregnant women and their developing fetuses, particularly in the Canadian general population. In contrast, manganese is an essential nutrient for human health, especially in pregnancy. Using the Maternal-Infant Research on Environmental Chemicals (MIREC) Study of 2,000 pregnant women, four such metals - cadmium, lead, manganese, and mercury - were measured in 1st and 3rd trimester maternal blood, umbilical cord blood, and meconium (infant's first stool). Consumption of nutrients was estimated by administering both a food frequency and a dietary supplement questionnaire. Trace amounts of cadmium, lead and mercury were detected in maternal blood. Other than cadmium, which was rarely measured in cord blood or meconium, average levels of the other metals were higher in cord compared to maternal blood. Manganese was found in all the biospecimens tested. Increasing maternal blood manganese was associated with higher blood cadmium, mercury and lead, especially in the 3rd trimester. Increasing calcium consumption was associated with lower maternal 3rd trimester cadmium, lead, manganese, and mercury, and cord blood lead. Higher consumption of vitamin D was associated with lower 3rd trimester maternal cadmium, lead, and manganese, and cord blood lead. These results showed that the distribution of metals between maternal and cord blood differed by metal, with far less transfer of cadmium from mother to fetus. Furthermore, consuming more dietary calcium and vitamin D during pregnancy may be associated with lower maternal blood lead and cadmium levels and lower lead levels in cord blood. These results can be used to establish normative levels of these metals in pregnancy and to support good nutrition in pregnancy. This study was published in the journal Chemosphere (2016 Nov;163:270-282).
Arsenic Levels among Pregnant Women and Newborns in Canada: Results from the Maternal-Infant Research on Environmental Chemicals (MIREC) Cohort
Health Canada helps to protect the health of Canadians by assessing and managing the health risks associated with exposure to environmental contaminants. Arsenic is a common environmental contaminant, and human exposure can be detected in various tissues. Of paramount concern, particularly with respect to health effects in children, is the timing of exposure, as the prenatal and early-life periods are more susceptible to toxic effects. The Maternal-Infant Research on Environmental Chemicals (MIREC) Study was established to obtain national-level biomonitoring data for pregnant women and their infants over a three-year period from 2008 to 2011 in 10 Canadian cities. Total arsenic in first and third trimester maternal blood, umbilical cord blood, and infant meconium (first stool), and arsenic in first-trimester maternal urine were measured. Most pregnant women (approximately 90%) had detectable levels of arsenic in their blood. Arsenic was less often detected in umbilical cord blood and meconium. Most of the different forms of arsenic that can be measured in urine were rarely detected except for dimethylarsinic acid (DMA). Among this population of pregnant woman and newborns, levels of arsenic measured in maternal blood and urine were lower than national population figures for Canadian women of reproductive age (20-39 years). In general, higher arsenic levels were observed in women who were older, foreign-born, and had higher education. Further research is needed to identify factors that may influence arsenic exposure in pregnant women and infants and evaluate potential health effects, if any. Health Canada will use the results of this study to inform future risk assessments and risk management of arsenic, especially regarding exposures during pregnancy. This study was conducted in collaboration with scientists from the Yale School of Public Health, the Institut national de santé publique du Québec, Université de Sherbrooke, and Sainte-Justine University Hospital Research Centre, University of Montreal. This work was published in the journal Environmental Research (2017 Feb;153:8-16).
Maternal Concentrations of Perfluoroalkyl Substances and Fetal Markers of Metabolic Function and Birth Weight
Health Canada helps to protect the health of Canadians by assessing and managing the health risks associated with exposure to environmental contaminants. Previous research has suggested that elevated maternal exposure to perfluoroalkyl substances (PFASs) may be associated with lower birth weight of their infants. PFASs are persistent pollutants widely used in the production of common household and consumer goods including cookware, clothing, and food packaging. The fetal time period is a window of increased sensitivity to the potential adverse effects of environmental contaminants. The objective of this study was to examine the potential association between maternal blood concentrations of three PFASs (perfluorooctanoic acid (PFOA), perfluorooctanesulfonate (PFOS), and perfluorohexanesulfanoate (PFHxS)) and infant birth weight. In addition, the association between maternal exposure to these contaminants and umbilical cord blood levels of two biomarkers of metabolic function, leptin and adiponectin, was examined. These two hormones may provide an indication of childhood growth patterns. Using the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, which was established to obtain national-level biomonitoring data for pregnant women and their infants over a three-year period from 2008 to 2011 in 10 Canadian cities, PFASs were measured in first trimester maternal blood of the MIREC women, whose pregnancies were followed through to delivery. Higher levels of PFOA in maternal blood were associated with reduced birth weight among both male and female infants, though the size of this effect was relatively low. Maternal concentrations of PFOS were associated with a modest decrease in cord blood leptin levels in both male and female infants. As the majority of North American women have detectable concentrations of these three types of PFASs in their blood, it is important to continue to assess the potential health risks of these chemicals. Following the MIREC children as they age will help determine whether the observed findings persist and manifest in any clinically significant manner. This study was led by scientists from Dalhousie University, with collaboration from Health Canada scientists and was published in the American Journal of Epidemiology (2017 Feb 1;185(3):185-193).
Associations of Prenatal Urinary Bisphenol A Concentrations with Child Behaviors and Cognitive Abilities
Health Canada helps to protect the health of Canadians by assessing and managing the risks associated with exposure to environmental chemicals. Prenatal bisphenol A (BPA) exposure has been associated with adverse effects in some studies but not others. However, few prior studies have examined the ability of children to learn and reason. This study measured BPA levels in urine of pregnant women enrolled in the Maternal-Infant Research on Environmental Chemicals (MIREC) Study. When the children born to these women were about 3 years of age, the study team measured the children's cognitive abilities using standardized tests of their intelligence (IQ) and executive function (ability to plan, organize, pay attention and remember things). Parents also reported information on their child's behaviour. The levels of BPA in the urine of the pregnant women were not associated with their child's IQ. However, the association between prenatal BPA exposure and scores measuring executive function was related to the sex of the child - a doubling of BPA level was associated with 1-point poorer working memory in boys and 0.5-point better scores in girls. BPA was also associated with anxiety, depression and somatic behaviours (experiences of physical symptoms that cannot be explained by underlying medical or neurologic conditions) in boys, but not girls. A doubling of prenatal BPA was also associated with worse scores on a test that measured interpersonal behaviours, communication, and repetitive or stereotypic behaviours in both boys and girls. Prenatal BPA levels were associated with some aspects of children's behaviour and working memory. However, the researchers cannot conclude that BPA caused these effects because they were not able to adjust for parental behaviour and IQ. In addition, BPA levels were only measured once during the pregnancy. Nevertheless, these results will add to the body of knowledge on potential neurotoxic effects associated with prenatal BPA exposure. This work was led by scientists at Brown University and published in the journal Environmental Health Perspectives (2017 Jun 16;125(6):067008).
Total Folate and Unmetabolized Folic Acid in the Breast Milk of a Cross-Section of Canadian Women
Folate requirements increase during pregnancy and lactation. Women who could become pregnant, are pregnant, or who are lactating are recommended to consume a folic acid (FA) containing supplement. The objective of this study was to determine breast milk total folate and unmetabolized FA (UMFA) content and to determine their relationship with FA supplement use and dose in Canadian mothers enrolled in the Maternal-Infant Research on Environmental Chemicals (MIREC) Study. Breast milk tetrahydrofolate (THF), 5-methylTHF, 5-formylTHF, 5,10-methenylTHF and UMFA were measured using LC-MS/MS in a subset of participants (n=561). Total daily supplemental FA intake was based on self-reported FA supplement use. The study found that UMFA was detectable in the milk of 96.1% of the women. Total daily FA intake from supplements was associated with breast folate concentration and species. Breast milk total folate was 18% higher (p<0.001) in supplement users (n=401) than non-users (n=160), a difference driven by women consuming >400 µg FA/day (p≤0.004). 5-methylTHF was 19% lower (p<0.001) and UMFA 126% higher (p<0.001) in supplement users than non-users. Women consuming >400 µg FA/day had proportionally lower 5-methylTHF and higher UMFA than women consuming ≤400 µg/day. This study demonstrated that FA supplement use was associated with modestly higher breast milk total folate and that detectable breast milk UMFA was nearly ubiquitous, including women who did not consume a FA supplement. Breast milk UMFA was proportionally higher than 5-methylTHF, a natural form of folate, in women who consumed >400 µg FA/day, suggesting that higher FA supplement doses exceed the physiological capacity to metabolize FA resulting in its preferential uptake in breast milk. FA supplement doses higher than 400 µg may therefore not be warranted, especially in populations such as in Canada where FA fortification is mandatory. This work was led by scientists at Health Canada and published in the American Journal of Clinical Nutrition.
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.
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