Photo by Josh Withers on Unsplash
Photo by Josh Withers on Unsplash

EXPERT REACTION: Is pesticide exposure as risky as smoking for some cancers?

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Living in a community with a high exposure to pesticides may come with an increased risk of some cancers that's comparable to smoking, according to US research. The team compared agricultural pesticide 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. The team says they found a link between pesticide exposure and an increased risk of any cancer, and more specifically leukaemia, non-Hodgkin's lymphoma, bladder, colon, lung and pancreatic cancers. The researchers say the risk from pesticide exposure is comparable to the risk from smoking for some of these cancers. However, below, Australian researchers say there is not enough scientific evidence to support this claim considering the well-known and major burden of cancers linked to smoking, and this type of research cannot show the higher community exposure to pesticides causes these cancers.

Journal/conference: Frontiers in Cancer Control and Society

Research: Paper

Organisation/s: Rocky Vista University, USA

Funder: The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article.

Media release

From: Frontiers

[TITLE] Pesticides potentially as bad as smoking for increased risk in certain cancers

[SUBTITLE] Researchers assessed the impact of commonly used agricultural pesticides on cancer incidence and found that pesticide use is associated with increased cancer risk

[SUMMARY] Pesticides have long been established as potentially health damaging, with some of them linked to cancer. In a populational US-wide study that considered not only farmers who actively use pesticides but communities as a whole, researchers contextualized cancer risk associated with pesticide use and smoking. They found that living in an environment heavily exposed to pesticides could increase the incidence of cancer as much as smoking.

[MAIN TEXT]

In modern day agriculture, pesticides are essential to ensure high enough crop yields and food security. These chemicals, however, can adversely affect plant and animal life as well as the people exposed to them.

Now, in a population-based, nation-wide study, researchers in the US have put increased cancer risk through agricultural pesticide use into context with smoking, a better understood cancer risk factor. The results were published in Frontiers in Cancer Control and Society.

“In our study we found that for some cancers, the effect of agricultural pesticide usage is comparable in magnitude to the effect of smoking,” said the study’s senior author, Dr Isain Zapata, associate professor at the Rocky Vista University, College of Osteopathic Medicine in Colorado.

Contextualizing cancer risk

“We accept that a person who is not a farmer living in a community with heavy agricultural production is exposed to many of the pesticides used in their vicinity. It becomes part of their environment,” Zapata said.

The researchers found that in such an environment, the impact of pesticide use on cancer incidence rivaled that of smoking. They strongest association was among non-Hopkins lymphoma, leukemia, and bladder cancer. In these types of cancers, the effects of pesticide exposure were more pronounced than the effects of smoking.

“We present a list of major pesticide contributors for some specific cancers, but we highlight strongly that it is the combination of all of them and not just a single one that matters,” Zapata pointed out.

Pesticide cocktails

Because pesticides aren’t used one at a time, the researchers said it is unlikely that one alone is to blame. Although some pesticides are discussed more frequently than others, all – and mostly their combination – can have an impact. Accordingly, the researchers included 69 pesticides for which use data is available via the United States Geological Survey. “In the real world, it is not likely that people are exposed to a single pesticide, but more to a cocktail of pesticides within their region,” Zapata said.

The researchers said their study is the first comprehensive evaluation of cancer risk from a population-based perspective at a national level. So far, no large-scale study had examined the big picture and put pesticide use in context with a cancer risk factor that is no longer questioned, in this case smoking. “It is difficult to explain the magnitude of an issue without presenting any context, so we incorporated smoking data. We were surprised to see estimates in similar ranges,” Zapata said.

Seeing the bigger picture

The researchers said that while their study extends knowledge about pesticide use in the US, cancer risk factors are complicated and assessing the big picture may not reflect individual outcomes. For example, geography has a strong impact. In regions where more crops are grown, such as the Midwest, which is famous for its corn production, the associations between pesticides and cancer incidence were more striking.

Getting people, also those who are not exposed to pesticides frequently, to think about the problems pesticide use poses in a bigger context is one of the researchers’ goals.

“Every time I go to the supermarket to buy food, I think of a farmer who was part of making that product. These people often put themselves at risk for my convenience and that plays a role in my appreciation for that product. It definitely has had an impact on how I feel when that forgotten tomato in the fridge goes bad and I have to put it in the trash,” said Zapata.

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Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

Professor Bernard Stewart is a Conjoint Professor with the School of Women's & Children's Health at the University of New South Wales and a scientific advisor to Cancer Council Australia.

Using a study titled Comprehensive assessment of pesticide usage patterns and increased cancer risk, to derive the headline Pesticides potentially as bad as smoking for increased risk in certain cancers, is little short of nonsense.

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. The study design cannot establish causation and no such modelling has been later confirmed for any putative carcinogen.

There is no recognition that pesticide exposure determines cancer risk in the general population as would justify this investigation. In the relevant publication there is no systematic reference to other epidemiological findings about particular pesticides. Thus while glyphosate carcinogenicity is restricted to non-Hodgkin lymphoma (NHL), this study records increased pancreatic and colon cancer but not NHL without acknowledging what’s already established.

The assertion that living in an environment heavily exposed to pesticides could increase the incidence of cancer as much as smoking is misleading because lung cancer is not the basis of the observation. That the observation applies only to NHL, leukaemia and bladder cancer largely invalidates the assertion because smoking does not cause NHL or leukaemia apart from the acute myeloid type. Suggestions that pesticide exposure could play a role similar to smoking and be more determinative of cancer than socioeconomic disparities are without merit.

Last updated: 25 Jul 2024 9:46am
Declared conflicts of interest:
None declared.
Terry Slevin is CEO of the Public Health Association of Australia and an Adjunct Professor at both Curtin University and ANU

The evidence linking some cancers with some pesticides is growing, particularly for those who regularly directly work with them.  Establishing the precise nature of that connection is scientifically challenging so there remains debate.  For some pesticides there is strong evidence of cancer link (Lindane and non-Hodgkins lymphoma being an example)

BUT – the decades of unequivocal evidence linking tobacco smoking with 16 different types of cancer is solid and well accepted.

It’s important to note that this 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.

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. I do not agree with the contention that these findings “show that the impact of pesticide usage on cancer incidence may rival that of smoking.”

Smokers are always well advised to quit, and non-smokers to not start smoking.  People who use pesticides – especially those who do so regularly as part of their work – are strongly advised to minimise their exposure to those chemicals through finding alternatives, or by minimising contact through proper PPE and careful handling.

Last updated: 26 Jul 2024 2:11pm
Declared conflicts of interest:
None declared.
Oliver Jones is Professor of Chemistry at RMIT University in Melbourne, Australia

The authors have identified a possible association between increase in risk of cancer and combined pesticide use by comparing existing data sets, not conducting new experimental work. 

While it is certainly interesting to look at combined rather than single exposure, as I see it, and as the authors themselves admit, there are several weaknesses to the study. 

Firstly it is important to keep in mind that the word pesticide is a catch all term for many different compounds, they are not all the same and they should be used with proper protective equipment.

Similarly, an association is not the same as causation. It is possible that something else is related to both agriculture and any potential increased cancer risk. However, if the proposed association was found to hold up by other studies then it might be worth trying to distinguish those pesticides with a stronger association with cancer from those with no association. This data could then be fed into risk assessment when choosing which pesticide to use.  

The authors state that organic farms do not use pesticides. This is incorrect. Organic farms do use pesticides, just different (usually less effective) ones than conventional farming. Examples include nicotine sulfate, methyl bromide, peracetic acid, and Veratran D. The amounts of pesticides used on organic farms are generally not recorded though. 

The study also seems to treat non-Hodgkin lymphoma as single cancer when it is actually a catch-all term for over 60 different subtypes. 

So, in short, a thought-provoking study that might well be worth further investigation, but it is not without limitations and should not be a cause for panic.

Last updated: 24 Jul 2024 2:48pm
Declared conflicts of interest:
Oliver has declared he has no direct conflicts of interest, however he declares receiving funding from the Australian Research Council and the water industry for some of his research work.
Dr Ian Musgrave is a Senior Lecturer in the Faculty of Medicine, School of Medicine Sciences, within the Discipline of Pharmacology at the University of Adelaide.

This paper attempts to identify cancer risks due to pesticide use by examining cancer rates in US counties with their rates of pesticide usage. This provides an association, but does not provide evidence of causation. The major issue is that there is no real quantitation of exposure, and it is assumed that the local usage level in agriculture equates to exposure to all people in that county.

Furthermore, 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.

As a reminder, glyphosate was suggested to be associated with cancer because of some small studies that did not achieve statistical significance [results may be down to chance]. Only with the large agricultural health study, where actual exposure to glyphosate could be determined, was it shown to have no effect on cancer rates.

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.

Last updated: 24 Jul 2024 2:46pm
Declared conflicts of interest:
None declared.
Dr Yousuf Mohammed is a Senior Research Fellow/Research leader at the Frazer Institute at the University of Queensland

The paper evaluates the effect of agricultural pesticide usage and cancer incidence across the United States from a population perspective. The authors also compare the area/county-based increase in cancer incidence that can be linked to pesticide usage to smoking.

Although the journal isn’t at the peak in the area, the topic potentially is sensational. In summary, the authors have used established and clearly defined tools to study the relative increase in cancer incidences (across leukaemia, non-Hodgkin’s lymphoma, bladder, colon, lung, pancreatic, cancers, and all cancers) in a population base.

They showed that the areas of the US with higher agricultural productivity had higher cancer risk due to pesticide usage. Their median rate per 100,000 people was found to be similar to reported data from CDC, demonstrating soundness of methods. The authors acknowledge that independent validation by others is required.

Last updated: 04 Dec 2024 11:10am
Declared conflicts of interest:
None declared.

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