Jan 12, 2010
As a chemist by training, I’ve always been loath to give credence to unfounded criticism of synthetic chemicals that might stoke up chemophobia. Indeed, on several occasions I have written about how our bodies have evolved to cope with all kinds of chemicals regardless of whether they are synthetic or “natural”. I’ve never been a shill for the chemical industry, although I have been accused of it. But, there is so much misguided nonsense about the supposed absolute risks of synthetic chemicals that someone has to provide a little balance.
On at least one occasion, however, I’ve been thwarted in my efforts to provide just such a balanced point of view the issues surrounding chemical safety. Once it was a blinkered features editor on a well-known popular science magazine who simply refused to see past the word “manmade” and had already decided that if the product being discussed wasn’t derived from an extract of hemp or some other natural material and squeezed out by native bushpeople or some such nonsense then it didn’t deserve a mention in the hallowed pages of the magazine.
As a science, chemistry is more than wonderful, it not only sates the inquisitive and repeatedly throws up new puzzles, it also provides us with the materials with which we have built the modern world. As with any human endeavour there is, of course, a price to pay. Many of the essential ingredients of the industrial processes on which our standard of living depends are toxic. There is no way to avoid that issue. Volatile organic compounds are a case in point and several of the most toxic are now banned substances on health and environmental grounds.
Toxicity, however, is about exposure and dose, not about blanket bans. That said, it is sometimes necessary to take a more holistic view of the potential impact of the chemical cocktails with which we surround ourselves in the workplace and in the home. Multiple-chemical sensitivity was a buzz-phrase back in the early 1990s and filled many a column inch in trade magazines such as Chemical & Engineering News (C&EN) and the now-defunct Chemistry in Britain. I’ve still got the pre-PDF “cuttings” mouldering away in a filing cabinet somewhere. But, this syndrome doesn’t seem to feature much in the trade or any other media these days, I suspect its clinical significance like so many other nebulous disorders simply didn’t stand up to close scrutiny. There are many people who will likely disagree, and certainly medicine is far from perfect, but the assumption intrinsic in MCS is that synthetic = bad, which really isn’t the case.
However, Dimosthenis Sarigiannis and colleagues at the European Commission – Joint Research Centre, at the Institute for Health and Consumer Protection, in Ispra, Italy, seem keen to resurrect the notion that mixtures of chemicals are somehow more worrying than a single chemical acting alone.
Writing in the International Journal of Risk Assessment and Management, they assert how current risk assessments address compounds individually whereas real-life human exposure is to mixtures of chemicals present in the environment, the workplace, or consumer products. They suggest that a more connected approach to chemical risk assessment is needed.
Such an approach would combine information from environmental fate analysis, epidemiological data and toxicokinetic models to help us estimate internal exposure. This information might also be coupled to gene expression profiles to provide a signature of exposure to whole classes of toxic compounds so that we might derive a biologically based dose-response estimate. Such an approach will take into account the non-linear relationship between risk and exposure to mixtures of toxic compounds, the team explains.
The team concedes that any such model of risk-exposure will need a large data set to ensure that its predictions are statistically robust. And, I agree that we need to overhaul risk assessment in light of better understanding of how chemical mixtures affect gene expression, metabolism, and other biological processes. They also explain that a linear, additive approach to mixture toxicology is entirely outmoded given the latest evidence on non-additive effects. Again, I agree. This is not chemophobia this is rational assessment.
Sarigiannis, D., Gotti, A., Reale, G., & Marafante, E. (2009). Reflections on new directions for risk assessment of environmental chemical mixtures International Journal of Risk Assessment and Management, 13 (3/4) DOI: 10.1504/IJRAM.2009.030697