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This essay is in response to: How is the developing fetus vulnerable to toxic chemical exposures, and how can our regulatory system more effectively protect our health in the prenatal period?
Recent publications in the scientific literature have highlighted the increasing evidence of adverse pregnancy outcomes due to environmental chemical exposures during pregnancy and the preconception period. Studies have definitively shown that the fetus is susceptible to exposure -- sometimes at many times the concentration in the mother -- with sometimes tragic results to childhood physical and cognitive development, future reproductive capacity, and the development of cancer. Publications in the lay press such as Living Downstream by Sandra Steingraber and Origins by Annie Murphy Paul have raised the awareness of patients who are looking to their personal physicians to advise them about how to prevent exposure and maximize the health of their offspring.
Although the reproductive health effects from exposure to the majority of the thousands of chemicals in current use are not known, evidence ranges from definitive to strongly suggestive that lead, some types of pesticides, mercury, and endocrine disrupting chemicals (EDCs) can adversely affect birth outcomes.
Lead
The health effects of exposure to lead during early childhood are well known. Studies showing the disruption of normal behavioral development and loss of IQ at blood lead levels below 10 ug/dl have led the Centers for Disease Control to propose lowering the action level to 5 ug/dl. In pregnancy, elevated maternal lead levels have been shown to result in neurodevelopmental outcomes similar to those seen in exposed children, as well as maternal gestational hypertension and increased risk for preterm delivery. Recently published guidelines from the CDC recommend screening at-risk women, and identifying and removing the source of exposure for those with blood lead >5ug/dl.
Pesticides
The group of chemicals called pesticides includes insecticides, herbicides, rodenticides, and fungicides. Strong evidence from studies of pregnant women living and working in agricultural settings shows that urine levels of pesticides are associated with lower IQ and poorer performance on other neuro-developmental tests in early childhood. Use of pesticides at home during the preconceptional period and during pregnancy is significantly associated with childhood leukemia. Exposure in both agricultural and inner-city environments leads to an increased risk of intrauterine growth restriction and low birth weight. Ecologic studies of residents who live in areas of high use of certain agricultural pesticides show higher rates of congenital anomalies.
Mercury
Mercury in the atmosphere from coal-fired power plants, waste incineration, and other industrial processes enters waterways and is metabolized by microorganisms into methyl mercury, which then accumulates in fish. In the United States mercury has contaminated 43% of US lakes and wetlands. In the past decade, several studies combining data on fish consumption frequency questionnaires and mercury levels in hair, blood, and cord blood, have estimated that between 5-8% of pregnant women may have mercury levels above the recommended limits. Mercury is a potent neurotoxin, and multiple studies show that low dose exposure from fish consumption among pregnant women can result in lower scores on the Denver Developmental test, the Bayley Psychomotor Development index, and the Neonatal Assessment Behavioral Scale.
Endocrine Disruptors
The potential health effects of endocrine disrupting chemicals (EDCs) have been recognized since diethylstilbestrol (DES), given to women to prevent miscarriages in the mid-twentieth century, resulted in uterine malformations and vaginal cancers in “DES daughters.” Other health effects discovered more recently include decreased fertility in both sons and daughters, and hypospadias and cryptorchidism in grandsons of DES recipients. More recently, plasticizers have received increasing attention as animal studies have shown that these substances can mimic or antagonize endogenous hormones, resulting in male and female reproductive tract abnormalities, and neurodevelopmental abnormalities. Exposure to EDCs in the US population is practically ubiquitous; the National Health and Nutrition Examination Survey (NHANES) has found phthalates in > 75% and bisphenol-A (BPA) in > 93% of participants over age 6. Polyfluoroalkyl chemicals (PFCs), used in food containers, lubricants, and “teflon” coated cookware, have been detected in > 98% of participants over age 12. Studies of blood donor samples shows that levels of some polybrominated diphenyl ethers (PBDEs), commonly used as flame retardants in household products, have increased in direct correlation to their production.
Because they appear in the blood of almost all US residents, there has been concern about the effects of EDCs on the developing fetus. Reproductive tract abnormalities in both males and females, and neurodevelopmental abnormalities are seen in studies of animals exposed to BPA. In human epidemiologic cohort studies, prenatal exposures to phthalates have been associated with male reproductive tract abnormalities. PBDE exposure during pregnancy has been associated with disruption of maternal thyroid hormone. Scientific articles reporting results of health outcomes from exposures to EDCs in pregnancy have mushroomed in the past 10 years. We will soon have sufficient data to bolster prevention efforts aimed at changing public policy, similar to successful efforts to decrease lead in gasoline and paint, and mercury from power plant emissions.
While exposure to lead, mercury, and some pesticides has decreased in recent decades, we are discovering subtle developmental and hormonal disruption at low doses. Preventing these health effects requires efforts by physicians and public health policy makers. Healthcare providers who take care of pregnant and preconceptional patients should screen their patients for exposures to substances known to harm the fetus. Questions about exposure to lead, mercury, and pesticide use in the home can help target advice about sources of lead, frequency of fish consumption, and avoidance of pesticide use at home. Public health professionals should continue efforts to monitor lead in homes and products and to advocate and legislate for decreased mercury emissions. They should promote alternatives to pesticides and demand legislation to update toxic substances regulation. Both physicians and public health professionals have an important role to play in protecting the fetus from harmful pollutants.
Acknowledgements to Judith Focareta, Sheela Sathyanarayana, and Perry Sheffield
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To those living in Montgomery County Maryland, please sign a petition calling upon the Montgomery County Council to act as a Board of Health to adequately protect our population and our environment from harmful effects of pesticides, by adopting a law that bans the use of harmful lawn and garden pesticides in Montgomery County, MD, equivalent to the Canadian Cosmetic Pesticide Ban of 2009. http://bit.ly/MoCoPesticideBan
February 14, 2012Dr. Buchanan, As a mother and a public health doctor, I'd like to thank you for providing such an excellent summary of the pollutants most likely to put fetal health at risk. Hopefully, commentary like yours will bring about better public health and environmental policy around toxins.
February 13, 2012