Environmental toxicants and fetal development is the impact of different toxic substances from the environment on the development of the fetus. This article deals with potential adverse effects of environmental toxicants on the prenatal development of both the embryo or fetus, as well as pregnancy complications. The human embryo or fetus is relatively susceptible to impact from adverse conditions within the mother's environment. Substandard fetal conditions often cause various degrees of developmental delays, both physical and mental, for the growing baby. Although some variables do occur as a result of genetic conditions pertaining to the father, a great many are directly brought about from environmental toxins that the mother is exposed to.
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 polychlorinated biphenyls, organochlorine pesticides, perfluorinated compounds, phenols, polybrominated diphenyl ethers, phthalates, polycyclic aromatic hydrocarbons, perchlorate PBDEs, compounds used as flame retardants, and dichlorodiphenyltrichloroethane (DDT), a pesticide banned in the United States in 1972, in the bodies of 99 to 100 percent of the pregnant women they tested. Among other environmental estrogens, bisphenol A (BPA) was identified in 96 percent of the women surveyed. Several of the chemicals were at the same concentrations that have been associated with negative effects in children from other studies and it is thought that exposure to multiple chemicals can have a greater impact than exposure to only one substance.
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.
Preterm birth One in ten US babies are born preterm and about 5% have low birth weight. Preterm birth, defined as birth at less than 37 weeks of gestation, is a major contributor 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.
Structural congenital abnormality
Toxic substances that are capable of causing structural congenital abnormalities can be termed teratogens. They are agents extrinsic to embryo or fetus which exert deleterious effects leading to increased risk of malformation, carcinogenesis, mutagenesis, altered function, deficient growth or pregnancy wastage.Daftary, Shirish; Chakravarti, Sudip (2011). Manual of Obstetrics, 3rd Edition. Elsevier. pp. 38-41. . Teratogens are classified in four main categories: Drugs in pregnancy – in addition to environmental chemicals, includes recreational drug use and pharmaceutical drugs. Vertically transmitted infections Radiation, such as 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.
Autism spectrum disorder (ASD) is a neurodevelopmental disorder that presents as deficits in social interactions, and communications. These deficits can vary in strength and impairment in day-to-day function. This could be alexithymia, aggressive behaviors, difficulty regulating emotions, repetitive behavior, and lack of empathy. ASD is known to have many factors some including epigenetic, genetic, and environmental. These findings regarding autism are controversial, however, with many researchers believing that increasing rates in certain areas are a consequence of more accurate screening and diagnostic methods.
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.
Alcohol Drinking alcohol in pregnancy can result in a range of disorders known as fetal alcohol spectrum disorders. The most severe of these is fetal alcohol syndrome. These two conditions can lead to a large range of defects that can affect the fetus physically, cognitively, neurodevelopmentally, and can cause neurobehavioral deficits. These changes are dependent on severity of alcohol use and the timing during gestation. The physical characteristics of FAS could include facial abnormalities, growth deficit, and dysfunction of central nervous system development. Even more so behavioral and emotional differences are also very common in patients with FAS.
Tobacco smoke
Fetal exposure to prenatal tobacco smoke may experience a wide range of behavioral, neurological, and physical difficulties. 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.
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. 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, methyl mercury was discharged into the waters of Minamata Bay, where it went on to be ingested regularly by many villagers who used the fish living in the bay as a dietary staple. Soon, many of the inhabitants who had been consuming the mercury-laden meat began experiencing negative effects from ingesting the toxin; however, the mercury especially impacted pregnant women and their fetuses, resulting in a high rate of miscarriage. Surviving infants exposed to mercury in-utero had extremely high rates of physical and intellectual disabilities, as well as physical abnormalities from exposure in the womb during key stages in fetal physical development. The United States Food and Drug Administration and the Environmental Protection Agency advise pregnant women not to eat swordfish, shark, king mackerel and tilefish and limit consumption of albacore tuna to 6 ounces or less a week.
High mercury levels in newborns in Gaza are theorized to originate from war weaponry.Manduca, Paola, Awny Naim, and Simona Signoriello. "Specific Association of Teratogen and Toxicant Metals in Hair of Newborns with Congenital Birth Defects or Developmentally Premature Birth in a Cohort of Couples with Documented Parental Exposure to Military Attacks: Observational Study at Al Shifa Hospital, Gaza, Palestine." International Journal of Environmental Research and Public Health. N.p., 14 May 2014. Web. 25 July 2014. <http://www.mdpi.com/journal/ijerph>.
Mercury exposure in pregnancy may also cause limb defects.
Lead Adverse effects of lead exposure in pregnancy include miscarriage, low birth weight, neurological delays, anemia, encephalopathy, paralysis, blindness,
The developing nervous system of the fetus is particularly vulnerable to lead toxicity. Neurological toxicity is observed in children of exposed women due to 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.
Cadmium Cadmium is a heavy metal that the United States Environmental Protection Agency classifies as a probable human carcinogen. People are often exposed to cadmium through various industrial and agricultural sources, and diet is considered the primary exposure method. The heavy metal has been shown to cause damage to the kidneys, bones, and neurological systems. Pregnant women are at higher risk of health issues from cadmium due to increased absorption of the metal during pregnancy. Cadmium can also pose health risks to the fetus, some of which may be lifelong, as it interferes with placental function and fetal development. There has been evidence of changes in birth size associated with high levels of cadmium exposure, particularly in female children. 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.
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.Facts about Dioxins. from Minnesota Department of Health. Updated October 2006
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.
Compounds such as carbon monoxide, sulfur dioxide and nitrogen dioxide all have the potential to cause serious damage when inhaled by an expecting mother. Low birth weight, preterm birth, intrauterine growth retardation, and congenital abnormalities have all been found to be associated with fetal exposure to air pollution. 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.
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.