17 December 2014

Dr Crispin Halsall argues that systematic reviews, commonly practiced in the world of medicine, could be equally useful in assessing the safety of chemicals. 

Determining whether a medical intervention works or not is nowadays highly dependent on subjecting the available evidence to a systematic review (SR). SRs have been instrumental in distinguishing effective treatments from ineffective ones; as such, SR techniques may be just the ticket to ensuring that risks associated with exposure to everyday chemicals are properly evaluated, using the best evidence to provide a transparent answer.

So I and Paul Whaley, a colleague from the Lancaster Environment Centre at Lancaster University, organised a workshop to explore this idea. Bringing together a disparate group of scientists and regulators is always an interesting affair. People are at ease describing their own field, but once you mix specialists up and create a discussion group about topics that are out of their comfort zone, then the fun really starts.

Hosted by the Royal Society of Chemistry in the lovely surroundings of Burlington House in central London, we managed to gather 34 specialists (including Prof Ian Boyd, the Chief Scientific Advisor to the Department For Environment, Food & Rural Affairs) with the aim of exploring the topic of ‘systematic review’ as applied to chemical risk.

What a dry topic, you might think.

But consider this: Bisphenol-A (BPA) is a common plasticiser present in the linings of food cans, plastic bottles etc. Because of its wide use in consumer goods and food contact materials, pretty much everyone is exposed to it pretty much all the time. It is also a suspected hormone disrupting agent, mimicking the activity of oestrogen to varying degrees at various hormone receptor sites. Its health effects seem to vary unpredictably depending on the organism studied, the time at which they were exposed, and/or the dose administered..

The problem is, different groups of scientists and regulatory bodies, using broadly the same toxicology studies, are at loggerheads over whether the chemical is safe or not! This is the case for many chemical substances and if the public is to have confidence in regulatory authorities then the system needs to change.

Borrowing from the world of medicine, we hope to adopt SR methods to properly assess the risks posed by chemicals present in our food and environment.

So what is systematic review? SR is a procedure for reviewing evidence which yields a reproducible method for determining what is and is not known in relation to a carefully poised question or hypothesis. It is almost like a tick list of jobs which a reviewer needs to follow in order to conduct a high-quality, credible, verifiable review of the evidence.

A question such as “Does exposure to BPA lead to an increase in hormonally-induced cancer?” would be addressed by following this procedure. It would begin with an explicit expression of how and where you are going to start your search for the literature, followed by a transparent statement of the criteria you are using to decide which studies are to be included in your review and which excluded.

Studies selected for inclusion would then be subject to a specific protocol to assess the quality of data/findings and to identify any risk of bias in each included study. A subsequent meta-analysis might ensue using the best possible data, which in turn will eventually answer the question, or at least identify knowledge gaps which might prevent an answer!

In our workshop, we brought together specialists from the worlds of epidemiology, toxicology, regulatory science and systematic review. Between presentations, a number of breakout sessions were held focusing on pragmatic approaches to applying SR to the world of chemical risk assessment, and the major challenges that these pose. So, back to mixing specialists up!

The discussion groups were lively and free flowing, and set the basis for a special issue of the journal Environment International, allowing workshop members to contribute full research papers as well as commentaries about this new field. Clearly this is horizon scanning at the moment, but momentum is gaining and plans are afoot to develop a network of scientists to push this field forward.

In the not too distant future, we hope SR will revolutionize how we assess chemicals present in our food and environment, giving the public reassurance about what is safe and what is not.


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