By Steven Mew, the Australian Science Media Centre
Research out of the US this week suggested that living in a community with a high exposure to pesticides may come with an increased risk of some cancers that's comparable to smoking, however the evidence might not be so clear cut, according to Australian experts.
The research, published in Frontiers in Cancer Control and Society, compared United States agricultural pesticide use data, cancer rates, and data on other cancer risks, including smoking, to estimate the relationship between living in an agricultural community with high pesticide use and eventual cancer rates.
But Professor Bernard Stewart, a Conjoint Professor at the University of New South Wales, who was not involved in the study, was critical of the way the study had been designed.
"In this study, cancer from pesticides is not determined by comparing cancer in people handling pesticides with those who don’t, but by correlating pesticide sales across US counties with respective incidences of different cancer types," he told the AusSMC.
Using this design, the researchers found a link between pesticide usage and an increased risk of any cancer, and more specifically leukaemia, non-Hodgkin's lymphoma, bladder, colon, lung and pancreatic cancers. The authors claim the risk from pesticide use is comparable to the risk from smoking, for some of these cancers.
However, Australian experts who independently evaluated the study in an AusSMC Expert Reaction, say there is not enough scientific evidence to support this claim considering the well-known and major burden of cancers linked to smoking.
Professor Stewart said the claim that living in an environment heavily exposed to pesticides could increase the incidence of cancer as much as smoking is misleading because they are not talking about lung cancer.
Instead, the paper found that by far the biggest increase in risk compared to smoking was for non-Hodgkin lymphoma (NHL) but according to Professor Stewart, "smoking does not cause non-Hodgkin lymphoma."
Mr Terry Slevin, CEO of the Public Health Association of Australia and Adjunct Professor at Curtin University and ANU suggested that while the evidence linking some cancers with some pesticides is growing, the specific interaction is scientifically challenging to determine and therefore is still under debate.
"BUT – the decades of unequivocal evidence linking tobacco smoking with 16 different types of cancer is solid and well accepted," he said.
According to Mr Slevin, it’s important to note that the study doesn’t prove that pesticides have caused specific cancers but looks broadly at cancer trends in geographic areas in the USA where pesticides are used.
"It’s a step-too-far from this level of analysis to suggest that the burden is comparable to tobacco, which causes more than 8 million deaths worldwide each year," he told the AusSMC.
"There is little scientific evidence to support a claim that exposure to pesticides is contributing to the cancer burden to anything like the level attributable to tobacco smoking."
Additionally, the very nature of the study's design means we need to be cautious about the conclusions we draw from its findings.
As Professor Oliver Jones from RMIT University and Dr Ian Musgrave from University of Adelaide were both quick to point out, 'an association is not the same as causation.' That is to say, finding that there is a link between pesticide use and cancer rates does not mean that pesticide use causes cancer.
"It is possible that something else is related to both agriculture and any potential increased cancer risk," Prof Jones told the AusSMC, while Dr Musgrave specified that the authors had not factored in other influences on the cancer rate.
"There are a number of factors that influence cancer development, such as air pollution, petrochemical exposure, etc. While adjustment for smoking was made in this study, a wide range of other potential confounders were not addressed," he said.
According to Dr Musgrave, the results of this study should be taken with extreme caution.
"If the effect were truly of the same order of magnitude as smoking, we would have surely seen it long before now."
The research was published just as Australia's federal court dismissed a class action claiming the common weed killer, Roundup is causing cancer.
You can read the full AusSMC Expert Reaction here.
This article originally appeared in Science Deadline, a weekly newsletter from the AusSMC. You are free to republish this story, in full, with appropriate credit.
Contact: Steven Mew
Phone: +61 8 7120 8666
Email: info@smc.org.au