Our modern lives are drenched in chemicals, some of which can mimic hormones in our body's endocrine system.
Obesity, type 2 diabetes, and some cancer rates are on the rise in humans. While sperm count and fertility is on a downward slide in some populations. What if chemical exposure was partly responsible for these trends?
One hypothesis is that a group of chemicals — known as 'endocrine disrupting chemicals' (EDCSs) — could affect human reproduction, puberty, metabolism and other functions controlled by hormones in our endocrine system.
Many suspected EDCs are already in your home — but how much risk do they really pose? At what exposure level do they become unsafe?
Unfortunately the answer is not straightforward, with a range of opinions held by scientists, industry and regulators.
In terms of scientific evidence, there are good laboratory studies that show some industrial chemicals affect endocrine function in mice and rats, and many examples of endocrine disruption in wildlife from chemicals in the environment.
However, it's a lot harder to get conclusive evidence that these chemicals do the same in humans. This is partly because studying the long-term effects of everyday chemicals on humans is difficult.
"We can't test in humans directly. That would be absolutely unethical, to expose someone to the chemical and go, 'How are you doing today? How about tomorrow?" said Associate Professor Frederic Leusch, an environmental toxicologist from Griffith University on this week's Science Friction.
We're also exposed to hundreds of chemicals each day — and these may interact in unforeseen ways.
Is there a safe level of exposure?
Professor Leusch said we just don't know what level of exposure to EDCs is safe. Although, he said, the body has a strong repair system and is more resilient than we give it credit for.
Dr Andrea Gore, an endocrinologist from The University of Texas is of the view that it is less about the level of exposure and more about the timing of the exposure.
"Classical toxicology has always followed the mantra of the dose makes the poison — a higher dose will be worse than a lower dose; and there is a lower limit of exposure where there would be no effect," Dr Gore said.
Current safety regulation of chemicals in Australia take this approach.
In a statement to Science Friction, the federal Department of Health said chemicals introduced into Australia are regulated through the National Industrial Chemicals Notification Scheme (NICNAS).
It said risk assessments of chemicals, including some phthalates and brominated flame retardants, are published on the NICNAS website.
"For each of these chemicals, the effects are dose-responsive. These well-characterised examples with a classical dose-response effect allow a safe level of exposure to be identified and risk mitigation measures put in place," it said in the statement.
But scientists like Dr Gore argue that the classical toxicology approach does not allow for the possibility that very low levels of exposure to an EDC could have long-term effects, particularly if the exposure occurred at times when humans are very sensitive to hormones, such as in the womb or at puberty.
"Endocrinologists … say the timing makes the poison," she said.
"You can take a very low level of a chemical that disrupts a hormone and if you expose it during a developmental time of life when your body might not normally be exposed to a natural hormone at all, the body can respond to that low dose."
Again, this is very hard to test in humans, said Professor Leusch.
"We're very, very long lived and it's very difficult to link in an exposure when you were five to an effect when you're 20," he said.
In the end there's a range of opinions on whether there's enough evidence to raise a red flag on EDCs.
But until more is known, it may be a good idea to minimise our exposure to potential EDCs, said Professor Leusch.
"Until we can figure out what the safe concentration is, where the threshold is, I think we should aim to get exposed to as little as possible," he said.
The following suggestions are some simple ways that may limit your exposure to potential EDCs in the home.
Eat fresh food, and wash your fruit and veggies
Fruit and vegetables can have residue from pesticides which may be EDCs. Simply washing your fruit and vegetables with water can remove most of these residues, Dr Gore said.
She also suggested eating fresh food over processed food, to reduce the risk of exposure to chemicals during processing.
"No matter how pristine processed organic spinach might be we don't know what chemicals it came into contact with while being processed — did it come into contact with detergents and packing chemicals? The recommendation is always fresh over processed."
Tin cans and jar lids are often lined with bisphenols, like BPA. And while many manufacturers are now making BPA-free products, Dr Gore said the chemicals being used to replace BPA may also present a risk.
"We know that many replacement chemicals are in the same family BPF, BPS are also endocrine disruptors," she said.
Watch out for plastic
Plastic can contain bisphenols like BPA and phthalates. To find out what your plastic container is made of, look for a number between one and seven somewhere on the packaging — the numbers 3 (PVC) and 7 (polycarbonate) are the ones to watch out for.
Heating plastic containers — such as microwaving a takeaway container, or leaving a water bottle in a hot car — can cause BPA to leach from the plastic, said Dr Gore.
Other suggestions are to avoid washing plastics with harsh detergents, which can cause the plastic to break down. Or opt for glass, porcelain or stainless steel over plastic containers.
Phthalates can be found in plastic food wrap, vinyl flooring and soft toys. Toys, baby bottles and dummies containing more than 1 per cent of the phthalate DEHP have already been banned in Australia.
While some countries like Australia have put some restrictions on the use of phthalates in toys, there is always a question over what is present in imported goods from countries with less regulation.
Minimise exposure through personal care products
Cosmetics and personal care products — such as perfumes, nail polish, skin creams, shampoo and conditioner — can contain some types of phthalates and parabens (chemicals used as preservatives). Antibacterial soaps and some brands of toothpaste can contain triclosan.
Check the ingredient listing for parabens or phthalates, and be wary of artificial fragrances which can contain phthalates. However, it's often difficult to know what chemicals are in personal care products, especially in fragrances — Australian suppliers are not required to list the individual components.
Using less products is one way to reduce exposure. Or make your own products using common household ingredients, such as bicarb soda and coconut oil.
Check out your furnishings, clothing, and non-stick products
Common household objects like your couch, mattress, water-proof clothing and non-stick cookware can contain potential EDCs in the form of flame retardants (such as PBDEs), stain and water resistant coatings (such as PFOAs), or non-stick coatings (PFCs).
"A lot of our products around the home are covered in these compounds that act as flame retardants should there be a fire," said Professor Leusch.
But, he said, there are ways to try to cut down your exposure to them.
"If you've got new carpets for example, I strongly recommend aerating the space quite thoroughly before so you don't breathe in that new carpet smell too much."
When buying new products, try to check what types of flame retardant or stain-resistant chemicals it contains. And with non-stick cooking products, make sure you use them to the manufacturer's specifications (which often include low temperature usage). A further precaution is to throw away products if the non-stick surface is damaged.
Keep your house clean, but with the right products
Cleaning products for everything from benchtops to the bathroom tiles can contain potential EDCs, such as 2-butoxyethanol and methoxydiglycol. If they contain artificial fragrance they may also contain phthalates.
There are many alternative cleaning products, such as baking powder as a general cleaner and deodoriser; lemon juice as a mild bleach; salt mixed with lemon juice or white vinegar to remove stains; or white vinegar as a deodoriser and mild disinfectant.
Another source of exposure in the home can be from a build-up of potential EDCs, such as flame retardants, in household dust. Regular vacuuming, wiping down surfaces with a damp cloth, ventilating rooms and regularly cleaning air conditioners, heater inlets and vents can help reduce exposure.
Green chemistry – the road ahead?
It's estimated that there are close to 100,000 manufactured chemicals in our world, and we have not tested every single one of them, said Dr Leusch.
He is concerned about us finding out too late when industrial chemicals are toxic, but acknowledges the benefits they offer us.
"Chemistry and chemical engineering have done wonders for our life. We have to find a middle ground."
Meanwhile, environmental health scientists, biologists and endocrinologists have started working with chemists to design chemicals that are don't mess with our endocrine system.
"If you want to understand and design a safe chemical that doesn't interfere with hormones, you actually need to know what a hormone is and how it acts and how to test it," said Dr Gore.