People are becoming more aware of and concerned about the dangers that even tiny quantities of chemicals may cause them – chemicals that are found in products we use every day, such as plastic water bottles, sunscreen and toothpaste.
You've probably heard about bisphenol A (BPA), which can be found in plastic containers we use to store our food and drink.
We know BPA affects our hormones, and it's been linked (although not conclusively) to all sorts of hormone-related health problems including asthma, obesity, diabetes, attention deficit hyperactivity disorder (ADHD), breast and prostate cancers, and reproductive abnormalities.
Because of its hormonal action, BPA is classified as an endocrine-disrupting chemical (EDC).
But it's not the only EDC you'll find in everyday items.
The endocrine system is a series of ductless glands that secrete hormones directly into the blood to regulate various bodily functions. The glands and the hormones they produce include:
- gonads – produce sex hormones (oestrogen and testosterone)
- thyroid – thyroid hormone
- adrenal – adrenaline
- pancreas – insulin
- pituitary – growth hormone.
Body fat, muscle, heart, liver, intestines and kidneys have secondary endocrine functions and also produce hormones.
Many substances affect our endocrine systems. When ingested (in food, for example), absorbed or inhaled into the body, these substances interfere with the production, action and/or elimination of our naturally present hormones.
Endocrine disorders are on the rise worldwide
Endocrine disorders include:
- low semen quality and fertility in young men
- genital malformations, such as non-descending testes (cryptorchidism) and penile malformations (hypospadias) in baby boys
- premature birth and low birth weight
- neurobehavioural disorders associated with thyroid disruption in children (autism, attention deficit disorders and learning disabilities)
- endocrine-related cancers (breast, endometrial, ovarian, prostate, testicular and thyroid)
- earlier onset of breast development in young girls, which is a risk factor for breast cancer
- obesity and type-2 diabetes.
Studies have confirmed EDCs as a cause of many of these disorders (though not all). In some cases, EDCs account for their increased incidence, too. Endocrine disorders have also been recorded in wild and domestic animals.
BPA may be one of the highest-profile endocrine disruptors, but we're regularly exposed to plenty of others, including:
- synthetic chemicals used as industrial solvents/lubricants and their byproducts (polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs), dioxins)
- plasticisers (phthalates)
- pesticides (methoxychlor, chlorpyrifos, dichlorodiphenyltrichloroethane (DDT) and tributyltin)
- fungicides (vinclozolin)
- pharmaceutical agents (diethylstilbestrol)
- fluorinated surfactants or perfluoroalkyl and polyfluoroalkyl substances (PFAS).
Although they're rarely classed as endocrine disruptors, natural substances such as soy and beta-sitosterol also have hormonal effects. Pharmaceuticals including menopause hormone therapy and the oral contraceptive pill have endocrine-disrupting effects, too.
Another concern is that, of an estimated 50,000 chemicals in use today, very few have been tested for endocrine effects. And only a small proportion of the 800 or so chemicals suspected to be endocrine disruptors have been tested.
Some types of pesticides are known endocrine disruptors.
Our age and developmental stage play a major role in how, or even if, endocrine disruptors affect us.
Humans and other animals are most vulnerable to EDCs during critical periods of development, such as during foetal development and puberty. And there can be a long time, even several generations, between exposure to an endocrine disruptor and when it takes effect. This means a pregnant woman's exposure may ultimately affect her grandchildren.
A pregnant woman's exposure may ultimately affect her grandchildren
In acknowledgement of the vulnerability of the developing foetus and infant, the Danish government has compiled an English-version consumer brochure for pregnant women.
This explains how to avoid exposure to known and suspected endocrine disruptors while pregnant and breastfeeding. It also explains how to keep your baby away from them too.
We’re most vulnerable to EDCs during key developmental stages such as foetal development and puberty.
There's lots we don't know about the effects of EDCs. For instance, researchers still struggle to establish whether a substance is an endocrine disruptor or not, and under what circumstances. But research has at least shed some light on EDCs.
Lots of information about endocrine disruption has come from lab animals, but animal testing doesn't always translate well from one species to another. For example, rats are more sensitive to some chemicals than other animals (including humans), yet less sensitive to others. Even within a species, some breeds are more sensitive than others.
Many endocrine disruptors have different effects at different doses. The problem arises when scientists only study very large doses and, if proven safe, assume the EDC is still safe at lower doses, too.
But there's growing evidence that very low doses of certain chemicals have an equal effect to high doses, or even a more potent effect. A medium dose, by contrast, may have no effect at all.
The other possibility is that the effect may be different, but equally damaging. For example, pregnant mice given large doses of an oestrogenic drug called diethylstilbestrol have extremely skinny offspring, whereas very low doses produce obese offspring. Alternatively, some endocrine disruptors may have an effect at medium doses, but have no effect at very high or very low doses.
Testing also often overlooks the combined effects of more than one EDC – they may magnify, change or cancel out any endocrine effects they have individually. This applies to products such as cosmetics or pesticides, which contain a raft of chemicals that could alter the effects of EDCs.
Studies on herbicides containing glyphosate, for example, found that the formulation of its containers was the major determinant of its endocrine effects, rather than the concentration of the glyphosate itself.
Test conditions versus normal use
Finally, just because a product contains known EDCs doesn't mean they'll be in a form that's harmful.
The Danish environmental protection agency tested various products containing EDCs, including mobile phone covers, work gloves, sleeping mats, sneakers and handbags, and found that the chemicals didn't migrate from the products under simulated conditions of normal use.
Just because a product contains known EDCs doesn't mean they'll be in a form that's harmful
On the other hand, for decades scientists assumed BPA wouldn't cause any problems because it was safely locked up in polycarbonate plastic – but when that plastic was heated or washed in harsh detergents, it released the BPA.
Some jurisdictions adopt a precautionary approach, meaning they ban known EDCs from some or all products and processes.
Relevant Australian authorities are taking a wait-and-see approach until there are more definitive research results – these include the Therapeutic Goods Administration (TGA), Food Standards Australia New Zealand (FSANZ), the Australian Pesticides & Veterinary Medicines Authority (APVMA), the National Industrial Chemicals Notification and Assessment Scheme (NICNAS), plus the various state and local environmental and water authorities.
- The Endocrine Society is an international organisation of professionals concerned with endocrinology research and clinical practice. Its members include clinicians, researchers, educators, industry professionals and health professionals. They have created a comprehensive review of the science behind endocrine disruptors.
- The World Health Organization (WHO) and United Nations Environment Programme's report on EDCs was released in February 2013.
- The Danish Ministry of the Environment has information and a consumer-friendly pamphlet (in English) for pregnant women on how to avoid EDCs.