⏳ Estimated Reading Time: 7 - 9 minutes

Describe endocrine disruptors and their effects on ecosystems.

The Endocrine System

The human endocrine system — **The endocrine system is not talked about as much as other body systems but can have wide-ranging effects on your health.**

Hormones regulate metabolism (insulin and thyroid hormones), growth and development (growth hormone), reproduction (testosterone and estrogen), homeostasis, and even our moods (serotonin, dopamine, endorphins). Even a slight imbalance in hormone levels can have significant health effects.

The endocrine system is a chemical messenger system in animals. It involves a series of feedback loops of hormones released by internal glands such as the hypothalamus, pituitary gland, and pineal gland among several other glands.

Hormones from these glands are released into the circulatory system and target organs in different parts of the body to help regulate them. When hormones are released from one of the glands, receptors in various organs and tissues recognize and respond to them.

Endocrine systems are found in all mammals and are also found in birds, fish, and many other types of living organisms.

There are several natural and human-made chemicals that can interfere with (disrupt) or mimic the normal hormones in an organism. This lesson focuses on problems caused in living organisms when the endocrine system is disrupted by these chemicals.

Endocrine Disruptors

Endocrine disruptors are chemicals that can interfere with (disrupt) the endocrine system of animals.

Exposure to endocrine disruptors may come through diet, air, skin, and water. Below are some common exposure routes:

released treated effluent from sewage treatment plants
leachate from landfills
consuming food and beverages
taking medicine
applying pesticides
using cosmetics
some plastics
gasoline

According to the EPA, the following chemicals at high exposure levels have been directly tied to endocrine disruptions:

organochlorine compounds (e.g., 1,1,1- trichloro-2,2-bis(p-chlorophenyl)
ethane (DDT) and its metabolite (DDE)
polychlorinated biphenyls (PCBs), and dioxins
some naturally occurring plant estrogens

In addition to the above, the National Institute of Health (NIH) cites the following as endocrine disruptors:

🍼 Bisphenol A (BPA) — used to make polycarbonate plastics and epoxy resins, which are found in many plastic products including food storage containers
📄 Dioxins — produced as a byproduct in herbicide production and paper bleaching, they are also released into the environment during waste burning and wildfires
🎇 Perchlorate — a by-product of aerospace, weapon, and pharmaceutical industries found in drinking water and fireworks
🍳 Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) — used widely in industrial applications, such as firefighting foams and non-stick pan, paper, and textile coatings
🪀 Phthalates — used to make plastics more flexible, they are also found in some food packaging, cosmetics, children’s toys, and medical devices
🥛 Phytoestrogens — naturally occurring substances in plants that have hormone-like activity, such as genistein and daidzein that are in soy products, like tofu or soy milk
🏠 Polybrominated diphenyl ethers (PBDE) — used to make flame retardants for household products such as furniture foam and carpets
🔌 Polychlorinated biphenyls (PCB) — used to make electrical equipment like transformers, and in hydraulic fluids, heat transfer fluids, lubricants, and plasticizers
🧴 Triclosan — may be found in some anti-microbial and personal care products, like liquid body wash

Looking at the list above, you can see that endocrine disruptors are all around us even though very few chemicals have been thoroughly tested for their impact on endocrine systems.

Essential Knowledge

Endocrine disruptors are chemicals that can interfere with the endocrine system of animals.

Impacts of Endocrine Disruptors

The effects of endocrine disruptors on cellular responses. The first diagram depicts increased hormones leading to a cellular response, the second shows hormone mimics binding to receptors, and the third presents hormone blockers altering hormone production. — ***Endocrine disruptors mimic natural hormones. These can fool the body into over-responding or under-responding to a stimulus.***

Concern about these pollutants has been increasing over the past few decades. Below are a few of the impacts found to be associated with endocrine disruptors:

🐣 Development Malformations (click to reveal)

An American alligator — **The most frequently reported effect of endocrine disruptors is estrogen mimicry. Florida alligators have been experiencing these effects since at least 1999.**

Endocrine disruptors can cause changes in fetal development, leading to birth defects or developmental disorders.

Effects from exposure to low levels of endocrine disruptors have been observed as well (e.g., parts-per-trillion levels of tributyl tin have caused masculinization of female marine molluscs such as the dog whelk and ivory shell).

Researchers have found that male alligators in Florida lakes have been experiencing feminization, likely due to exposure to endocrine-disrupting contaminants (Guillette, et al. 2000).

Growth hormones have been used in the livestock and poultry industry for years to get animals to grow faster and bigger to maximize profits. These chemicals that mimic growth hormones may cause an over-response leading to increased muscle mass when none were needed.

In Silent Spring, Rachel Carson detailed how DDT caused a decrease in eggshell thickness in raptors, such as bald eagles and peregrine falcons (1962).

🍼 Reproductive Issues (click to reveal)

A drawing of a pregnant woman holding her belly surrounded by endocrine disruptors, like plastics. — **Pregnant mothers can easily be exposed to endocrine disruptors.**

Endocrine disruptors can affect fertility and reproductive health, potentially causing conditions like endometriosis or reduced sperm quality.

Lavender and tea tree oil have been found to be potential endocrine disruptors. Researchers have found that persistent exposure to lavender oil resulted in atypical breast development in females and males (multiple publications by Ramsey, JT et al. 2017-2023).

Prior to its ban in the early 1970s, doctors mistakenly prescribed DES to as many as five million pregnant women to block spontaneous abortion and promote fetal growth. Researchers have found that the drug DES can alter the way genes are turned on and off in the reproductive organs, providing a possible explanation for how these chemicals disrupt reproduction and fertility (Jefferson, et al. 2018).

Phthalates have been linked to increased rates of preterm birth in non-white groups, likely caused by increased exposure to phthalates (Welch et al. 2023).

🦠 Increased Cancer Risk (click to reveal)

Exposure to certain endocrine disruptors has been linked to an increased risk of some cancers, particularly those related to the hormonal system like breast and prostate cancer.

Prior to its ban in the early 1970s, doctors mistakenly prescribed DES to as many as five million pregnant women to block spontaneous abortion and promote fetal growth. It was discovered after the children went through puberty that DES affected the development of the reproductive system and caused vaginal cancer.

💉 Immune System Disturbances (click to reveal)

Endocrine disruptors can affect the immune system, leading to increased susceptibility to infections or immune-related conditions.

Studies indicate that children exposed to high levels of PFAS have a diminished response to vaccines (Grandjean et al. 2017).

🧠 Neurological Effects (click to reveal)

Endocrine disruptors can impact the nervous system, potentially leading to learning disabilities or cognitive impairments.

Researchers have found that ordinary exposure to certain phthalates, as found in urine samples, was associated with ADHD-related behaviors in adolescence (Shoaff, et al. 2020). The drug DES may be linked to an increased chance of developing ADHD in the grandchildren of women who used it during pregnancy (Kioumourtzoglou, et al. 2018).

🩸 Metabolic Effects (click to reveal)

Endocrine disruptors can contribute to obesity, diabetes, and other metabolic diseases (Martin et al.).

More research and studies are needed on endocrine disruptors, especially when it comes to their effect on humans. Hopefully in the future, we will have a better handle on these fairly new pollutants.

Essential Knowledge

Endocrine disruptors can lead to birth defects, developmental disorders, and gender/imbalances in fish and other species.

AP Exam Tip

Endocrine disruptors are ubiquitous and can cause a wide range of effects in humans and living organisms.

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