EDCs and Their Impact on Human Health

What Are Common Endocrine Disruptors?

The human population is daily exposed to a wide range of EDCs that can interfere with endocrine functions. Many of these chemicals are associated with the development of breast, testicular and ovarian cancers as well as metabolic diseases such as obesity.

Molecularly, EDCs share structural similarities to natural hormones and interact with nuclear steroid receptors. Common examples include polychlorinated biphenyls (PCBs), dioxins, phthalates and diethylstilbestrol (DES).

1. Pesticides

Endocrine disruptors are chemicals that interfere with the hormone system in humans and cause a wide variety of health problems, such as attention deficit hyperactivity disorder (ADHD), Parkinson’s and Alzheimer’s diseases, obesity, metabolic disorders including diabetes, cardiovascular disease, cancer and immune system impacts. They can mimic the actions of natural hormones, block or prevent their action by blocking the hormone receptors in cells or by altering synthesis, transport, metabolism and excretion.

Many endocrine disruptors are bio-persistent, meaning that they do not break down quickly in the environment. In one study, we measured metabolites of organophosphate, pyrethroid and phenoxy herbicides in urine from 619 reproductive-age women using liquid chromatography-tandem mass spectrometry. We found that higher levels of these metabolites were associated with an increased likelihood of endometriosis diagnosis.

2. Polychlorinated Biphenyls (PCBs)

EDCs include natural and human-made chemicals that mimic, block or interfere with the body’s hormones. They often bind to hormone receptors and cause the normal signaling process to be overstimulated. They can also bind to the enzymes that make or break down hormones, such as estrogens or androgens.

Studies of cell cultures, laboratory animals and wildlife have documented the effects of EDCs. It has been more difficult to demonstrate EDC impacts on humans, but there is evidence that they exist.

PCBs contaminate soil and water, and because of their chemical inertness and high lipid solubility, they bioaccumulate in the fat tissue of top food chain consumers (i.e. predatory fish, large mammals, humans). They have been shown to disrupt thyroid and reproductive function in men and women.

3. Triclosan

Triclosan is an antimicrobial chemical added to many household and industrial products to prevent bacterial and fungal growth. It is absorbed through the skin and can be ingested. It is also a moderate skin sensitizer and has been shown to interfere with thyroid hormone production.

Animal studies show that triclosan can reduce thyroid hormone levels. It is also of concern because it crosses the placenta and enters breast milk. It has been detected in human plasma, urine and fish tissues at low doses.

NTP scientists use a broad range of laboratory tests to evaluate chemicals for their potential to disrupt the hormone system. NTP also has been collaborating with other federal agencies, such as the Environmental Protection Agency (EPA), to develop integrated high-throughput testing strategies for screening chemicals for their ability to interact with hormones.

4. Bisphenol A (BPA)

Bisphenol A (BPA) is an endocrine disruptor that mimics or partly mimics naturally occurring hormones like estrogens and androgens in the body. It also binds to hormone receptors and blocks their normal function.

BPA is a chemical used to make certain hard plastics and epoxy resins that line metal cans and some baby bottles. It can leach into food when heated. It’s found in some polycarbonate water bottles and infant bottles marked with the recycling code “7.” It’s also found in some plastic food containers, napkins, and cash register receipts.

Studies show that low doses of this chemical can cause health effects in animals and humans. NIEHS and the National Toxicology Program are assessing BPA and other EDCs, including pesticides, perfluorinated chemicals, compounds that could replace BPA in the market, and flame retardants.

5. Flame Retardants

The body’s endocrine system produces hormones that regulate a wide variety of functions like metabolism, growth, development and reproduction. Chemicals that interfere with this system are called endocrine disruptors.

The vast majority of the endocrine disruptors scientists have tested are flame retardants. When chemists like Arlene Blum first showed that toddlers had 15 times higher levels of one type of flame retardant, brominated tris, in their urine than their mothers, regulators banned it from baby pajamas. But manufacturers simply switched to similar chemicals that scientists hadn’t evaluated yet.

These chemicals are added to furniture foam, electronics and building insulation to meet flammability standards set by government regulations. They can be mixed into the base material (additive flame retardants) or chemically bonded to it (reactive flame retardants). Some have been linked to cancer, hormone disruption and adverse developmental, behavioural, neurological and immune effects in humans and wildlife.

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