September 23, 2026

expert reaction to study looking at chemical production volumes, sources, intake levels, emissions of breast-cancer relevant chemicals

Scientists comment on a study, published in Environmental Health Perspectives, looking at chemical production volumes, sources, intake levels, emissions of breast-cancer relevant chemicals.

Prof Michael Antoniou, Professor Emeritus of Molecular Genetics and Toxicology, King’s College London, said:

“Commercial pesticide (herbicide, insecticide, fungicide) formulations used both in agricultural and urban/domestic settings, are complex mixture of chemicals consisting of a stated pesticidal “active ingredient” and various co-formulants. The co-formulants perform various functions but collectively allow the active ingredient to more effectively exert its pesticidal action on the target pests (weeds, insects, fungi). There is now a large body of evidence from laboratory studies in cultured cells and more importantly in regulatory relevant animal systems, including work from my own research group, which shows that commercial pesticide formulations are far more toxic than the active ingredient alone – demonstrating that the co-formulants are highly toxic. Nevertheless, government regulatory agencies are yet to fully consider co-formulants as part of their risk assessment of pesticides. Co-formulants are rarely listed on commercial pesticide packaging as there is no regulatory obligation to do so. Instead, regulators focus exclusively on setting exposure limits for a given pesticide based on the stipulated active ingredient alone. Regulators require companies to conduct long-term toxicity studies in animals only with the active ingredient and not with the commercial formulations, to which people and environment are exposed.

“With this in mind, the findings of Kay and colleagues of the Silent Spring Institute are of high public health relevance. In a previous study published by the same group in 2024, the authors scrutinized several reliable US government and other international agency databases and based on experimental evidence identified over 900 chemicals that could pose a breast cancer risk. Although the data identified was from on cell culture and animal studies, they are of regulatory relevance. It is unethical to conduct toxicity studies in humans and thus regulators rely on results from investigations in cultured cells and more so in laboratory animals to set safety limits of exposure to toxic chemicals. Kay and colleagues have now built on this previous investigation by identifying possible sources of exposure to these potential or known breast cancer-associated chemicals. Using the latest available information from US government agency databases, they garnered information on the amount of a given chemical’s production, its uses, its routes of release into the environment, and estimated the level of its presence in people’s bodies based on actual measures in the US population. The study is well-executed and is unique in the range of measures it has undertaken, hence its publication in the top toxicology journal. They discovered that pesticides constitute a major source of exposure to breast cancer-associated chemicals, which included both active ingredients and co-formulants. They identified numerous sources of exposure to these pesticide ingredients, including food, drinking water, household and garden products, insect repellents, pest-control products for lice, athlete’s foot treatments, and sanitizers. Perhaps surprisingly, pesticides were also found in building materials. In their press release, the study’s lead author accurately reflets the concerns raised by their findings, which show that people are being exposed with carcinogenic chemicals, and further investigations should look into whether this accounts for some of the increased incidence of breast cancer.

“The limitation of the study by Kay and colleagues is common to all human biomonitoring and epidemiological studies – they provide associations and not definitive evidence that exposure to a chemical or chemicals causes any given illness. However, when combined with laboratory studies where animals are exposed to the same chemicals and they cause ill health, then the data from the biomonitoring and epidemiological studies is significantly strengthened. Thus, the current study, when combined with the experimental data presented in this group’s 2024 publication as well as many others demonstrating toxicity and disease from pesticide exposure, strengthens the argument for a link with breast cancer.

“The findings of Kay and colleagues may be of relevance to the UK population. My group has conducted the only pesticide biomonitoring study of UK citizens. We analysed the urine of 130 subjects living in different locations for 186 common insecticide, herbicide, and fungicide residues. We found that 53% were positive for the herbicide glyphosate and 100% positive for pyrethroid and organophosphate insecticides. Thus, similarly to what Kay and colleagues describe for US citizens, the UK population also seems to be exposed to a large cocktail of pesticides, which may have long-term health implications.   

“Overall, the findings of the study by Kay and colleagues highlight yet again that regulators should adopt more extensive risk assessment practices that include commercial pesticide formulations, and not just the declared active ingredients, in order to put in place measures to better protect people and the environment.”

Prof Oliver Jones, Professor of Chemistry, RMIT University, said:

“In my view, this paper is rather alarmist in nature. Little evidence is provided, and what is there is quite subjective. They also use terms like “pesticide”, which is catch all term for anything used to control pests and includes hundreds of different substances with vastly varying levels of risk.

“No new research has been performed; the authors have created a list of chemicals based on existing data from lab-based cell and animal models and then estimated possible exposure to chemicals. They did not actually measure concentrations of chemicals in people.

“Just because something can possibly happen under certain circumstances (e.g. high concentrations in an animal model) doesn’t mean that it does so in everyday life. For example, alcohol and UV rays in sunlight are both class one carcinogens. It does not mean a glass of wine or going outside is going to give you cancer.  Similarly, just because something is present in the environment does not automatically mean it is causing harm.  A chemical can be detected without it automatically meaning it will give you cancer. It is also incorrect to say that risk assessors don’t take mixture effects into account. Chemists and toxicologists are aware that there is more than one chemical in the world at a time. This is partly why they build in large safety factors into chemical risk assessment.

“Increased cancer rates could be the result of a number of things, such as a result of our success in reducing premature deaths from other causes. This is because cancer is primarily a disease of aging; the longer you live, the higher the likelihood that you develop some form of cancer. Thus, if we prevent people dying young from preventable diseases with vaccines and/or reduce road deaths by requiring seat belts, then more people live to the age when cancer risk goes up, and so cancer detection will increase. This possibility, nor any other alternative explanation, is not discussed in the paper.

“Overall, while the paper has a laudable goal, science should be objective. Oversimplification is not helpful to discussions on chemical safety and may even cause unnecessary public concern.”

‘Guiding Risk Reduction for Breast Cancer-Relevant Chemicals (BC 2 Chems): Chemical Production Volumes, Sources, Intake Levels, Emissions, and Regulations’ by Jennifer E. Kay et al. was published in Environmental Health Perspectives at 13:00 UK time on Wednesday 23 September 2026.

DOI: 10.1021/EHP.6c00022

Declared interests

Prof Michael Antoniou:
“I have not received any funding from industry of relevance to this subject. The pesticide toxicology work conducted in my group was funded by environmental and health charities namely the Sustainable Food Alliance (USA), the Sheepdrove Trust (UK) and Breast Cancer UK. 

I have served as a consultant on glyphosate risk assessment issues as part of litigation in the US over glyphosate-based herbicide health effects.

I received support from industry, Millipore-Sigma (USA), for clinical biotechnology research. “

Prof Oliver Jones: “My group is active in environmental pollution research. I have previously received funds from the Environment Protection Authority Victoria and various Australian Water utilities for research into environmental pollution. I am also a current member of the National Health and Medical Research Council (NHMRC) Water Quality Advisory Committee.”