Environmental toxicants and fetal development
Environmental toxicants and fetal development is the impact of different
Various toxins pose a significant hazard to fetuses during development. A 2011 study found that virtually all US pregnant women carry multiple chemicals, including some banned since the 1970s, in their bodies. Researchers detected
Effects
Environmental toxicants can be described separately by what effects they have, such as structural abnormalities, altered growth, functional deficiencies, congenital neoplasia, or even death for the fetus.[2]
Preterm birth
One in ten US babies is born preterm and about 5% have low birth weight. Preterm birth, defined as birth at less than 37 weeks of gestation, is a major basis of infant mortality throughout childhood. Exposures to environmental toxins such as lead, tobacco smoke, and DDT have been linked with an increased risk for spontaneous abortion, low birth weight, or preterm birth.[3]
Structural congenital abnormality
Toxic substances that are capable of causing structural
- pharmaceutical drugs.
- Vertically transmitted infections
- X-rays
- Mechanical forces, such as oligohydramnios
Teratogens affect the fetus by various mechanism including:
- Interfering with cell proliferation rate, such as viral infection and ionization
- Altered biosynthetic pathways, as seen in chromosomal defects
- Abnormal cellular or tissue interactions, as seen in diabetes
- Extrinsic factors
- Threshold interaction of genes with environmental teratogens
Neurodevelopmental disorder
Neuroplastic effects of pollution can give rise to neurodevelopmental disorders.
Many cases of
Toxicants and their effects
Substances which have been found to be particularly harmful are lead (which is stored in the mother's bones), cigarette smoke, alcohol, mercury (a neurological toxicant consumed through fish), carbon dioxide, and ionizing radiation.[7]
Alcohol
Drinking alcohol in pregnancy can result in a range of disorders known as
Tobacco smoke
Fetal exposure to prenatal tobacco smoke may experience a wide range of behavioral, neurological, and physical difficulties.[9] Adverse effects include stillbirth, placental disruption, prematurity, lower mean birth weight, physical birth defects (cleft palate etc.), decrements in lung function, increased risk of infant mortality.[7]
Mercury
Elemental mercury and methylmercury are two forms of mercury that may pose risks of mercury poisoning in pregnancy. Methylmercury, a worldwide contaminant of seafood and freshwater fish, is known to produce adverse nervous system effects, especially during brain development. Eating fish is the main source of mercury exposure in humans and some fish may contain enough mercury to harm the developing nervous system of an embryo or fetus, sometimes leading to learning disabilities.[10] Mercury is present in many types of fish, but it is mostly found in certain large fish. One well-documented case of widespread mercury ingestion and subsequent fetal development complication took place in the 1950s in Minamata Bay, Japan. Used by a nearby industrial plant in the manufacture of plastics,
High mercury levels in newborns in Gaza are theorized to originate from war weaponry.[12]
Mercury exposure in pregnancy may also cause limb defects.[3]
Lead
Adverse effects of lead exposure in pregnancy include miscarriage, low birth weight, neurological delays, anemia, encephalopathy, paralysis, blindness,[3][7]
The developing nervous system of the fetus is particularly vulnerable to lead toxicity. Neurological toxicity is observed in children of exposed women as a result of the ability of lead to cross the placental barrier. A special concern for pregnant women is that some of the bone lead accumulation is released into the blood during pregnancy. Several studies have provided evidence that even low maternal exposures to lead produce intellectual and behavioral deficits in children.[13]
Cadmium
Cadmium is a heavy metal that the United States Environmental Protection Agency classifies as a probable human carcinogen.[14] People are often exposed to cadmium through various industrial and agricultural sources, and diet is considered the primary exposure method.[15] The heavy metal has been shown to cause damage to the kidneys, bones, and neurological systems.[16] Pregnant women are at higher risk of health issues from cadmium due to increased absorption of the metal during pregnancy.[17] Cadmium can also pose health risks to the fetus, some of which may be lifelong, as it interferes with placental function and fetal development.[18] There has been evidence of changes in birth size associated with high levels of cadmium exposure, particularly in female children.[19] Although studies show that relatively low levels of cadmium exposure can affect pregnancy outcomes, more studies must be done to confirm these effects, establish updated exposure limitation guidelines, and explore ways to decrease exposure, particularly during pregnancy.[20]
Dioxin
Dioxins and dioxin-like compounds persists in the environment for a long time and are widespread, so all people have some amount of dioxins in the body. Intrauterine exposure to dioxins and dioxin-like compounds have been associated with subtle developmental changes on the fetus. Effects on the child later in life include changes in liver function, thyroid hormone levels, white blood cell levels, and decreased performance in tests of learning and intelligence.[21]
Air pollution
Air pollution can negatively affect a pregnancy resulting in higher rates of preterm births, growth restriction, and heart and lung problems in the infant.[22]
Compounds such as carbon monoxide, sulfur dioxide and nitrogen dioxide all have the potential to cause serious damage when inhaled by an expecting mother.[23] Low birth weight, preterm birth, intrauterine growth retardation, and congenital abnormalities have all been found to be associated with fetal exposure to air pollution.[24] Although pollution can be found virtually everywhere, there are specific sources that have been known to release toxic substances and should be avoided if possible by those who wish to remain relatively free of toxins. These substances include, but are not limited to: steel mills, waste/water treatment plants, sewage incinerators, automotive fabrication plants, oil refineries, and chemical manufacturing plants.[23]
Control of air pollution can be difficult. For example, in Los Angeles, regulations have been made to control pollution by putting rules on industrial and vehicle emissions. Improvements have been made to meet these regulations. Despite these improvements, the region still does not meet federal standards for ozone and particulate matter. Approximately 150,000 births occur every year in Los Angeles. Thus, any effects air pollution has on human development in utero are of great concern to those who live in this region.[25]
Pesticides
Pesticides are created for the specific purpose of causing harm (to insects, rodents, and other pests), pesticides have the potential to cause serious damages to a developing fetus, should they be introduced into the fetal environment. Studies have shown that pesticides, particularly fungicides, have shown up in analyses of an infant's cord blood, proving that such toxins are indeed transferred into the baby's body.[28] Overall, the two pesticides most frequently detected in cord blood are
A 2013 review of 27 studies on prenatal and early childhood exposures to organophosphate pesticides found all but one showed negative neurodevelopmental outcomes. In the ten studies that assessed prenatal exposure, "cognitive deficits (related to working memory) were found in children at age 7 years, behavioral deficits (related to attention) seen mainly in toddlers, and motor deficits (abnormal reflexes), seen mainly in neonates."[29]
A systematic review of neurodevelopmental effects of prenatal and postnatal organophosphate pesticide exposure was done in 2014. The review found that "Most of the studies evaluating prenatal exposure observed a negative effect on mental development and an increase in attention problems in preschool and school children."[30]
In 2017, a study looked at the possible effects of agricultural pesticides in over 500,000 births in a largely agricultural region of California and compared their findings to birth outcomes in other less agriculturally dominated California areas. Overall, they found that pesticide exposure increased adverse birth outcomes by 5–9%, but only among those mothers exposed to the highest quantities of pesticides.[31]
Benzenes
A 2011 study found a relationship between Neural Tube Defects and maternal exposure to
Other
- Heat and noise have also been found to have significant effects on development.[7]
- Carbon dioxide – decreased oxygen delivery to brain, intellectual deficiencies[7]
- Ionizing radiation – miscarriage, low birth weight, physical birth defects, childhood cancers[7]
- Environmental exposure to IQ in the child.[34]
Avoiding relevant environmental toxins in pregnancy
The American College of Nurse-Midwives recommends the following precautions to minimize exposure to relevant environmental toxins in pregnancy:[35]
- Avoiding paint supplies such as stained glass material, oil paints and ceramic glazes, and instead using watercolor or acrylic paints and glazes.
- Checking the quality of the tap water or bottled water and changing water drinking habits if necessary.
- If living in a home built before 1978, checking whether lead paint has been used. If such is the case, paint that is crumbling or peeling should not be touched, a professional should remove the paint and the site should be avoided while the paint is removed or sanded.
- To decrease exposure to pesticides; washing all produce thoroughly, peeling the skin from fruits and vegetables or buying organic produce if possible.
- Avoiding any cleaning supply labeled "toxic" or any product with a warning on the label, and instead trying natural products, baking soda, vinegar and/or water to clean.
Natural gas development
In a rural Colorado study of
In Pennsylvania, unconventional natural gas producing wells increased from zero in 2005 to 3689 in 2013. A 2016 study of 9384 mothers and 10946 neonates in the Geisinger Health System in Pennsylvania found prenatal residential exposure to unconventional natural gas development activity was associated with
Role of the placenta
The healthy
Identifying potential hazards for fetal development requires a basis of scientific information. In 2004, Brent proposed a set of criteria for identifying causes of
- Well-conducted epidemiology studies consistently show a relationship between particular effects and exposure to the substance.
- Data trends support a relationship between changing levels of exposure and the specific effect.
- Animal studies provide evidence of the correlation between substance exposures and particular effects.[40]
See also
References
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- ^ a b c d e f g ATSDR (January 17, 2013). "Principles of Pediatric Environmental Health: How Can Parents' Preconception Exposures and In Utero Exposures Affect a Developing Child?". Centers for Disease Control and Prevention.
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Further reading
- Agin, Dan (2009). More Than Genes: What Science Can Tell Us About Toxic Chemicals, Development, and the Risk to Our Children. New York: Oxford University Press. ISBN 978-0-19-538150-4.
- Buelke-Sam, Judy; Kimmel, Carol A., eds. (1994). Developmental Toxicology (2nd ed.). New York: Raven Press. ISBN 0-7817-0137-6.
- Chudley, T. V. N.; Persaud, A. E.; Skalko, Richard G. (1985). Basic Concepts in Teratology. New York: Alan R. Liss. ISBN 0-8451-0241-9.
- Schardein, James L., ed. (2000). Chemically Induced Birth Defects (3rd ed.). New York: Marcel Dekker. ISBN 0-8247-0265-4.
- Steingraber, Sandra (2001). Having Faith: An Ecologist's Journey to Motherhood. Cambridge, MA: Perseus Publishing. ISBN 1-903985-14-5.