Unexpected chemical contaminants found in human milk: McGill study

A new study from researchers at McGill University has found unexpected chemical contaminants in human milk.

Researchers looking into milk from Canada and South Africa have found that chemicals within the milk contained traces of pesticides, antimicrobials, and additives used in plastics and personal-care products.

“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 at McGill.

Previous studies looked at individual substances and the health consequences of exposure, while this study used a non-target analysis to conduct a broad search for any unusual chemical residues. Researchers were able to find the following compounds:

• 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).

Additionally, in samples from South Africa, researchers also detected 8-hydroxyefavirenz, a breakdown product of a medication called efavirenz used to treat HIV.

Researchers highlight that these compounds had not been previously reported in human milk.

“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.

Researchers add that this information could help improve chemical safety regulations and protect infant and parental health by expanding testing targets, while also encouraging further research to better understand how certain chemicals are metabolized in the human 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.

“Human milk is considered the gold standard for infant nutrition,” added Jonathan Chevrier, study co-author and associate professor of epidemiology at McGill. “It is therefore essential to understand everything infants are exposed to during this critical window of susceptibility in development.”

For the study, just under 600 human milk samples were collected in Canada (Montreal) and South Africa (Vhembe and Pretoria) between 2018 and 2019.