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ENDOCRINE DISRUPTORSÂ
produced by the placenta and the corpus luteum in the early days of a pregnancy, has many roles including protecting the fetus from the mother’s immune cells. Estrogen production during pregnancy increases greatly, and is a key player in placental development, as well as in establishing the blood circulation between the uterus and the placenta. Thyroid hormones, produced by the mother and the fetus, are critical for the development of the fetal and neonatal brain. Endocrine disruptors are any substance, natural or synthetic, that disrupts the synthesis, metabolism or transport of natural hormones. One of the first cases that struck the imagination and was the gateway for the study of endocrine disruptors is that of the insecticide DDT. This was used in several countries to fight against all kinds of insect pests, including mosquitoes carrying malaria. An American biologist, Rachel Carson, began in the late 1950s to take an interest in the dangers of DDT, when several birds died in Cape Cod after heavy use of DDT. She has written one of her best selling books describing how DDT enters the food chain and accumulates in adipose tissue. In Silent Spring, she relates the endocrine disrupting effects of DDT. Among other things, the exposure of birds to DDT decreased the activity of an enzyme, carbonic anhydrase, which is a key enzyme in eggshell formation. As a result, the shells were thinner and more fragile, so the eggs were very often damaged, and the reproductive success of several species was greatly affected. The work of several scientists, including Rachel Carson, led to the ban of DDT in the 1970s. Are human populations also exposed to endocrine disruptors, and if yes, is this exposure associated with any negative health outcomes? So far, we know that these substances have the ability to change the hormonal balance of several species, including humans, and that this imbalance is at the root of many diseases. We also know that human populations are exposed in various ways to these compounds. Endocrine disruptors are found in cosmetics (e.g paraben), plasticizers (e.g Bisphenol A), everyday products, pesticides, etc. Endocrine disruptors have been found in maternal and cord blood, as well as in the urine of pregnant women and in breast milk. A lot of endocrine disruptors can pass through the placenta,
therefore exposing the fetus. However, exposure to an endocrine disruptor (or any other environmental contaminant) does not necessarily mean a negative health outcome will be caused by this exposure. This will depend on the levels of exposure to this contaminant, as well as its capacity to be toxic. In the field of endocrine disruptors, we don’t have all the information required to be certain of a cause and effect relationship between exposure to these substances and negative birth outcomes.
What we know is that exposure to endocrine disruptors has been associated with altered reproductive function, increased incidence of some cancers such as breast cancer, preterm birth, low birth weight babies, neurodevelopmental delays in children, impacted immune function and obesity. These health outcomes are often multifactorial, but exposure to endocrine disruptors may contribute to the development of those pathologies. Another challenge scientists are facing when investigating the impacts of these substances, is that the potential health consequences of exposure to endocrine disruptors may happen later in life.
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