What also sets them apart from many other women is that they use fewer personal care products – which makes them an interesting subject for a scientist studying exposure to environmental chemicals.

When Dr Shanna Swan, Professor of Preventive Medicine from Mount Sinai School of Medicine in New York City, tested the urine of ten Old Order Mennonite women, she found that, compared to the average American, it contained lower levels of synthetic chemicals such as phthalates and bisphenol A. Both chemicals are hormone disruptors which means that at certain doses they can interfere with human and animal hormones. Pthalates have been linked to problems with male sperm, for instance, and bisphenol A - or BPA- has been linked to obesity and diabetes.

Shanna Swan attributes the Mennonite's lower levels of these chemicals not only to fewer cosmetics, but other lifestyle differences including less processed foods – pthalates and BPA are sometimes used in food packaging.

The question here is how much does this matter? If you happen to have lower levels of these chemicals in your body does it makes you less vulnerable to some health problems compared to someone whose levels are higher? We don't know - and that's the trouble with environmental chemicals: there are plenty of concerns and suspicions but also a lot of 'don't knows'. While experts might have figured out what the safe level of some  individual chemicals is for humans to ingest, a bigger question is how safe – or unsafe – is it for humans to be exposed to a mix of so many synthetic  chemicals from so many different sources from pesticides in food to chemicals in cosmetics, food packaging and frying pans?

It's an issue so big and so complex that it sometimes feels like the only thing to do – short of joining the Old Order Mennonites - is stick your head in the sand and ignore it. But then along comes Toxin Toxout, a new book by Canadian environmental activists Bruce Lourie and Rick Smith that helps to make some sense of it all and leaves you feeling slightly less powerless.

In their earlier book Slow Death by Rubber Duck, the authors used themselves as guinea pigs to see how changing their exposure to everyday environmental chemicals absorbed through the skin or from food affected the levels of these chemicals in their bodies. But in Toxin Toxout, the emphasis is on how we can reduce our exposure to these chemicals – and being selective with personal care products is one.

Lourie and Smith - who write about Shanna Swan's experiment with the Mennonite women in their book - also do some testing of their own and show that when volunteers switch from using conventional personal care products to more natural and organic products their levels of phthalates and parabens drop very quickly.

Among their other suggestions for limiting exposure to synthetic chemicals:

• Eat more organic food to avoid pesticides whenever you can and wash fruit and vegetables well before eating. (Incidentally, a small Australian study from RMIT's School of Health Sciences reported in April found that one week of eating mostly organic food reduced organophosphate pesticide levels in urine by 89 per cent.)
•  Use natural fibres and green products like low VOC (volatile organic compounds) paint in your home. Avoid vinyl products and furniture made with polyurethane foam. Clean and dust interior surfaces frequently and use a vacuum cleaner with a HEPA filter (a type of filter that captures ultra-fine particles).
• Exercise. Although we flush out some toxins in urine, others including some pesticides can be stored in fat. But according to Canadian researcher Dr Stephen Genuis from the University of Alberta – exercise helps release toxins from fat cells so that they're excreted via sweat and lung exhalation.

Bruce Lourie is speaking at the Sydney Writers' Festival at 10am Saturday May 24 and 9am Sunday May 25.

Toxin Toxout is published by University of Queensland Press, $29.95

smh.com.au