“The dose makes the poison…”
Public fear about the health and safety of chemicals is not new.
In today’s world, this fear is often generated by published reports linking chemicals to various illnesses or effects and drawing assumptions about the relevance of animal studies to people.
What is sometimes missed in these reports and what some people remain unaware of is the basic principle of toxicology that “the dose makes the poison”.
Concerns are sometimes raised about the presence of a tiny amount of a substance that is not hazardous to humans unless it’s consumed in large doses. There is also a commonly held view that synthetic chemicals are of more concern, even when the same chemicals exist in nature.
Many chemical substances, natural and synthetic, have an intrinsic hazard. In fact, many naturally occurring substances that are essential for good health and are fine in small doses, e.g. vitamin A, can cause great harm if taken in too large a dose.
One of the most important concepts regulators have to explain is that the actual risk to human health and safety is the product of the hazard times the exposure, in the case of food safety, to exposure through the diet.
Hazard is defined by international bodies such as the World Health Organisation as the potential of a substance to cause harm. For example, we know from very well characterised research that heavy metals, such as lead, can cause a hazardous effect on the human fetus and we know that exposure to lead results in harm to the human fetus, resulting in a high risk to human health and safety (i.e. risk = hazard x exposure).
Chemicals such as heavy metals occur naturally in the environment so exposure to very low amounts is unavoidable. The challenge is to mitigate the risk by developing effective risk management strategies to maintain levels of these chemicals as low as is reasonably achievable (known as the ALARA Principle). Even for the heavy metals, if there is low exposure, there is low risk. So again the message is the “dose that make the poison”.
The current debate on the safety of exposure to low levels of the chemical substance Bisphenol A (BPA), is an interesting example of a substance where the exposure is extremely low but fears have been generated by some studies.
BPA has been widely and safely used for many years in a wide range of products including food and beverage packaging.
It has been associated with many deleterious effects on endocrine and reproductive systems (BPA is regarded by some scientists as an “endocrine disruptor”), cardiovascular disease, diabetes and cancer, and the list is ever expanding. However, recent comprehensive risk assessments on all the available data on BPA, undertaken by the US Food and Drug Administration, and the European Food Safety Authority, have concluded that there is little potential hazard for BPA and that exposure is very low, leading to a very low risk to human health and safety.
To illustrate the point about the importance of levels of dietary exposure, research clearly indicates that levels of BPA found in food are in the parts per billion range. Liver enzymes are very efficient at combining with BPA, making 99.9% of it non-toxic, and it’s excreted in the urine so people of all ages are exposed to extremely low levels (in the range of parts per billion to parts per trillion – that’s 1 part in 1,000,000,000,000), which is the equivalent to taking a bucket of water out of Sydney Harbour). At such tiny levels of exposure to BPA, it is highly unlikely there is any risk to human health and safety.
The challenge for regulators the world over is to fill in the information gaps that result when some reports are published and reported on. We must communicate science in a way that acknowledges consumers’ concerns using language the community understands.
FSANZ has prepared consumer information on a range of chemical substances including BPA.
From the desk of the Chief Scientist - Food Standards Australia New Zealand:
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