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What scientific studies prompt regulatory action?

20 May 2011

The media often reports scientific studies that suggest possible links between pesticides and human health conditions. These are a subset of a wider range of studies that consider the potential impacts of a diverse set of factors from mobile phones to ultra violet radiation – on human health.

The key question we all face when reading of such studies is that of reliability and relevance. We want to know how strong the evidence is and whether the finding is relevant to our lives. At the back of our minds we also want to know that some Government agency is keeping an eye on things and will take action if necessary.

How do Government agencies, particularly those responsible for matters with a public health dimension, assess these studies? Perhaps more importantly, what would trigger a response?

A United States epidemiological study in 2010 that suggested that the herbicide atrazine may be a risk factor for the birth defect gastrochisis is a good example.

What evidence do regulators use?

Regulators use science-based information to make decisions. Typically, this information is provided by scientific studies.

But not all studies are of the same quality and value. Toward one end of the reliability/relevance continuum are epidemiological studies that use statistical correlations to suggest risk factors. Many of these studies are speculative in nature and have known forms of bias and error. They are useful for identifying potential hazards or hypothesis generation, but they cannot determine cause and effect.

Toward the other end are laboratory-based studies that demonstrate direct cause and effect relationships using real life contexts.

Any study that can be consistently replicated by other researchers and deliver the same results is highly valued. So too is the case when the scientific community develops a consensus around the causes of a particular condition.

Regulators are cautious about responding to epidemiological studies in isolation. They will, on the other hand, always respond to experimental studies that demonstrate direct causal relationships that can be replicated by other researchers where there is a scientific consensus.

Atrazine and gastrochisis?

The study suggesting a link between atrazine and gastrochisis was an epidemiological study. In looking at cases of gastrochisis it observed a very weak statistical relationship between month of birth and the season when a chemical such as atrazine would be applied in an adjoining agricultural area. No experimental studies were undertaken and no explanation was provided as to how atrazine might promote gastrochisis.

Another relevant factor is that no one knows what causes gastrochisis. Other epidemiological studies have proposed a range of other risk factors. These include recreational drug use, low maternal age at birth, infection, smoking, multiple sexual partners and use of aspirin and oral decongestants. Using the same statistical methods, the relationship between some of these factors and gastrochisis was found to be much stronger. For aspirin, for example, the association was over ten times greater.

But perhaps the strongest argument against atrazine causing gastrochisis is the fact that there is a scientific consensus – built from decades of research and thousands of experimental studies – that atrazine does not cause birth defects.

So, while the APVMA read and considered the study, it decided that its current set of management prescriptions for the safe use of atrazine was sufficiently protective and that no further changes were required. Other regulators have taken a similar position.

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Last updated on 27 May, 2011
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