An interdisciplinary team including researchers at McGill University has found a range of unexpected chemical contaminants in human milk samples from Canada and South Africa. The chemicals include traces of pesticides, antimicrobials and additives used in plastics and personal-care products. The findings were published across five papers.
"It is important to note that these chemicals were detected at low concentrations, and we do not fully understand the health effects of many of them. So, despite these findings, breast milk remains ideal for infants, as it has the nutrients infants need to develop as well as antibodies that protect them against diseases," said Stéphane Bayen, study co-author and Associate Professor in the Department of Food Science and Agricultural Chemistry.
The researchers said the data could help improve chemical safety regulations and protect infant and parental health by expanding testing targets. The information could also encourage further research to better understand how certain chemicals are metabolized in the human body.
Search for unusual residues
While earlier studies have often focused on individual substances and the health consequences of exposure, the researchers used a non-targeted analysis to conduct a broad search for any unusual chemical residues.
In this way, several new compounds were found, including:
- Antimicrobial preservatives (2-ethylhexyl 4-hydroxybenzoate and phenyl paraben) commonly added to soaps, disinfectants and personal-care products
- Plastic-related antioxidant additives (Irganox 1010 and BHT-COOH) used during manufacturing to stabilize plastics and packaging materials
- Pesticide-related or antimicrobial compounds: an agricultural herbicide (propanil) and an antimicrobial used in disinfectants and household products (chloroxylenol).
These compounds had not been previously reported in human milk.
In samples from South Africa, the researchers also detected 8-hydroxyefavirenz, a breakdown product of a medication called efavirenz used to treat HIV.
"To our knowledge, the compound had never before been identified in human milk. Its presence suggested that the mothers in South Africa used efavirenz during or prior to the sample years. This treatment was replaced by another regimen after 2019," Bayen said.
Analyzed samples in Montreal and South Africa
The researchers analyzed 594 human milk samples collected in Canada (Montreal) and South Africa (Vhembe and Pretoria) between 2018 and 2019.
They used different data-mining strategies in combination with high-resolution mass spectrometry, a technique that precisely identifies molecules in complex samples, to explore and identify unexpected or unknown contaminants in the body.
"Our results highlight - perhaps unsurprisingly - that populations are exposed to a complex cocktail of chemical residues, reflecting each individual's diet, environment and lifestyle," Bayen said.
He added that establishing baseline data is a necessary step toward reducing unwanted exposures.
The team also found that breast milk concentrations of certain chemicals, such as bisphenol A and bisphenol AF, were associated with altered growth among South African infants, highlighting potential adverse effects of exposure to breast milk contaminants. However, Jonathan Chevrier, Associate Professor of Epidemiology, cautions: "This is the first study of this type and so results need to be replicated before any conclusion can be drawn."
"Human milk is considered the gold standard for infant nutrition. It is therefore essential to understand everything infants are exposed to during this critical window of susceptibility in development," Chevrier said.
About the studies
"Breast milk bisphenol concentrations in Canada and South Africa and associations with body size among South African infants," by Basant Elsiwi, Stéphane Bayen, Zhi Hao Chi, Cynthia G. Goodyer, Barbara F. Hales, Bernard Robaire, Riana Bornman, Muvhulawa Obida Erica E.M. Moodie, and Jonathan Chevrier, was published in Environmental Research in November 2025.
"Application of non-targeted analysis for the identification of uncommon or unreported chlorinated contaminants in human milk," by Zhi Hao Chi, Ronan Cariou, Solène Motteau, Bruno Le Bizec, Gaud Dervilly, Lan Liu, Jingyun Zheng, Lei Tian, Jonathan Chevrier, Riana Bornman, Muvhulawa Obida, Cindy Gates Goodyer, Bernard Robaire, Barbara F. Hales and Stéphane Bayen, was published in Exposome in September 2025.
"Suspect screening of bisphenol A (BPA) structural analogues and functional alternatives in human milk from Canada and South Africa," by Zhi Hao Chi et al, was published in Nature: Journal of Exposure Science & Environmental Epidemiology in June 2025.
"Investigation of common and unreported parabens alongside other plastic-related contaminants in human milk using non-targeted strategies," by Zhi Hao Chi et al, was published in Chemosphere in May 2024.
"Biomonitoring of bisphenol A (BPA) and bisphenol analogues in human milk from South Africa and Canada using a modified QuEChERS extraction method," by Zhi Hao Chi et al, was published in Environmental Pollution in May 2024.
The research was funded by the Canada Foundation for Innovation/John R. Evans Leaders Fund, the Canadian Institutes of Health Research and a Canada Research Chair in Global Environmental Health and Epidemiology (J. Chevrier).
