2 years ago
30 March, 2021
Whether pesticides have toxic effects and cause breast cancer is a burning question, both for the scientific community and for consumers who want to lead a healthy lifestyle.
A pesticide can be a weedkiller used to clear invasive weeds in agricultural fields. It can also be a fungicide or an insecticide. Pesticides are not only sprayed in agricultural fields but also in private or public gardens, on rail tracks, industrial sites, golf courses, or even on verges of most cities.
In a recent scientific study 1, grass samples from playgrounds and schoolyards in Italy were found to be contaminated by dozens of pesticides. Some of them are known endocrine disrupting chemicals with harmful properties that raise questions about their potential role in breast cancer development.
Pesticides are generally linked to modern agriculture. Farmers who apply pesticides in their fields are often criticised by individuals or environmental organisations, causing growing resentment. This is sometimes known as ‘agribashing’. We should not neglect the challenges farmers are facing. The toxic effects of pesticides in farming communities are well known. The largest agricultural study conducted in the US has identified a link between the use of some insecticides and breast cancer risk among farmers’ wives 2.
Investigating the role of pesticide exposure in breast cancer development for women working on farms should be a priority. Women represent a large proportion of the agricultural workforce. Women may have a greater risk of pesticide exposure than men, as suggested in a study of Latina farmworkers in the US 3. It was found that women are often less protected than men when they handle pesticides because they have difficulty accessing properly fitting personal protective equipment typically designed for men.
Consuming fruits and vegetables grown on organic farms will certainly reduce an individual’s pesticide exposure. This is not very surprising. However, some major sources of pesticide exposure are closer to home. The inconvenient truth is that large quantities of insecticides are bought to kill mosquitoes, clothes moths, or other inconvenient bugs. When blood or urine tests reveal exposure to a dangerous dose of pesticide, the source is often domestic.
Ask yourself, is this mosquito on the wall worth pesticide exposure? Some flea and tick collars for dogs contain doses of insecticides sufficient to kill approximately 1 billion honey bees or a thousand partridges. The use of these collars is a major source of insecticide exposure 4. Ask yourself if your dog really needs it.
New clothes are also frequently contaminated by pesticides sprayed on cotton or because they are included in protective treatments during manufacturing. Always wash new clothes before wearing them.
Another problem is that pesticide screening in blood or urine is almost never done. Even after decades of controversies surrounding the toxic effects of pesticides 5, it is still not clear whether exposure at low doses present in the environment can cause diseases.
The sources of exposure to pesticides are multiple and difficult to evaluate. We are exposed to different doses of pesticides at different moments of our lives. It is difficult to predict when the toxic effects of pesticides can manifest. We studied the effects of glyphosate on breast cancer cells with the support of BCUK. This was an important study because of the debates surrounding glyphosate carcinogenicity, but we only scratched the surface as dozens of pesticides are used in the UK6.
The development of breast cancer can be initiated in the womb by toxic exposures, but these are only detected after a few decades.
The most reliable strategy to evaluate the adverse effects of pesticides in human populations is not to conduct animal studies or survey food for pesticide residues but to directly measure pesticide exposure by blood or urine screening. One of the few surveys performed in the US showed that high blood levels of the banned insecticide DDT predicted a 5-fold increased risk of breast cancer 7. Despite the worrying signs from this study, the presence of pesticides in the UK population has never been evaluated. There is an urgent need for human monitoring of pesticides.
Pesticide exposures are difficult to avoid. However, there is a lot we can do to reduce risks. Small actions, such as seeking information, or reconsidering the use of toxic chemicals in your house, may have significant consequences!
Written by Dr Robin Mesnage, who is a Research Associate in the Department of Medical and Molecular Genetics at King’s College London. He is a computational toxicologist whose main research interest focuses on understanding the effects of pollution on human health. Mesnage is also a consultant, providing expert advice on the risk assessment of pesticides. He is also a member of Breast Cancer UK’s Independent Scientific Review Panel.
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