How toxic are the chemicals we use?

PUBLISHED : Sunday, 06 November, 2011, 12:00am
UPDATED : Sunday, 06 November, 2011, 12:00am


What if your water bottle was making you fat? What if it could be giving you cancer or increasing the chances of your child being born with deformed genitals?

Welcome to the disquieting world of endocrine disrupters, chemicals that mess with the normal functioning of your hormone system. They can be found in flame retardants, cosmetics, pesticides, plastics and a host of daily personal care products.

While toxicology has thought the dosage makes the poison, scientists are finding more evidence that the dosages - once considered safe - of chemicals used in daily products may harm our health and alter the genetic destiny of future generations.

'What hormones do, particularly as the fetus is developing, is they turn genes on and off,' says John Peterson Myers, the founder, chief executive and chief scientist at Environmental Health Sciences in Virginia. 'The timing of turning genes on and off is absolutely crucial ... it makes sure your brain gets wired correctly ... and makes sure you turn out to be the right sex.

'Turns out, they behave the same way [as natural hormones]. Low doses turn genes on and off, high doses are poisonous,' said Myers, who was invited by Greenpeace Hong Kong to give a lecture at Hong Kong Baptist University last week.

With this new information, scientists like Myers are postulating that environmental contaminants may be adding to worldwide epidemics of obesity, infertility, type 2 diabetes and cancer. They may even cause the behavioural disorders like autism by altering the way our genes are expressed as we age.

On Myers' computer screen are a fat mouse and a normal mouse from a study at the US National Institutes of Health on an endocrine-disrupting chemical called diethylstilbestrol (DES). Genetically identical mice ate the same amount of food and moved about the same amount - but those exposed to DES at birth became obese at middle age.

The DES affected how the gene was expressed. 'There's this pool of stem cells, which when it's hit with a particular hormone, it becomes a fat cell. This particular pool makes a choice, either it's bone or fat. DES makes it become fat,' Myers said.

It's a simplified view of a complex chain of reactions that hormones can incite in a cell, but it shows the physiological change that happens when different levels of hormones, hormone mimickers or other types of endocrine-disrupting chemicals (EDCs) are introduced.

A 2007 study by Duke University geneticist Randy Jirtle showed that rats exposed to bisphenol A, a common additive in plastics used to line food cans, were born with a yellow coat instead of the more common brown and were more prone to obesity. Geneticist Pat Hunt found that mice exposed to BPA were more likely to suffer miscarriages. While it's too early to see whether certain endocrine disrupting chemicals, like BPA, affect the human genome in the same way, there is evidence that other factors are affecting how genes are expressed.

Susan Murphy, a Duke University expert in epigenetics, or the study of how genes are regulated, found that mothers who smoked during pregnancy had smaller babies. She said the chemicals reduced the activity of the gene that normally encourages cell growth in early development - in male babies only. 'Why it was just the male babies, I don't know.'

Her research showed the effects may be reversible, she said, but other studies indicate the chemicals we are exposed to now could change the way genes are expressed to other generations. 'When a woman is pregnant, the baby that is developing inside is developing gametes [what becomes eggs or sperm],' she said.

'Those gametes now are also exposed to whatever the mother has eaten and the mother's environment is she's smoking cigarettes. So it's not just affecting the mom herself with the direct exposure and the baby she's carrying, but it's also affecting the next generation,' Murphy said.

For these reasons, Greenpeace and scientists like Myers are working to limit such chemicals by reducing consumer demand and working with chemical producers, particularly 'green chemists'.

There are different ways green chemists operate, but the part that's applicable to EDCs is the idea of designing against hazard.

'Now you're involved in a fight over one chemical or another. Very often, less is known about the potential replacement than the thing you're trying to replace ... so you're in this awkward situation where you know you have to find something safer, but the choices are molecules that have been using the same criteria - flawed criteria - that were used to design the bad thing,' Myers said.

'[Green chemists] as they're designing a molecule, maybe they're looking at the shape and say: 'Wait a minute that looks like oestrogen, I don't want to use that. Boom - don't even bother to work with it, save money by even refusing to work with it,' said Myers. 'This is a vision - we see the pieces, but we don't have all of them in place ... the possibility of creating an entirely new generation of materials that are inherently safe.'

Of course, with so many chemicals in the world it's hard to say whether this approach is feasible.

Rudolph Wu Shu-sun, director of the school of biological sciences at University of Hong Kong, says the combined effects of EDCs in the human body are 'not known' because there are different types of chemicals with various effects. But he says it is also impractical to remove all endocrine-disrupting chemicals from the environment as the cost is too high.

'If the damage is very small, like a couple of beers, but you derive a lot of pleasure from it, then you go for it. For example, carcinogens. How about barbecue? How about smoked salmon? You still eat the thing.'

But he adds: 'If the consequence is something we cannot bear - such as the deformity of babies, death, cancer, even if the probability is very low - we still need to reduce the risk [of exposure].'

So while the animal studies, and evidence from statistical analysis are not enough of a smoking gun to say EDCs cause health problems, even the scientists are avoiding what they can, advising those pregnant to be particularly careful.

'Looking at my can of green beans in the cupboard,' said Murphy. 'I think, 'Well that would be good with dinner.' But I'll pass and get the broccoli out of the fridge that's fresh.'