New research suggests that breastfeeding may expose some children to toxic chemicals, Medical News Today.

Researchers at Harvard University found that perfluorinated alkylate substances (PFAS), a class of industrial chemicals linked with cancer and interference with immune function, appear to build up in infants by 20 to 30 percent for each month they're breastfed.

PFASs are used to make products resistant to water, grease, and stains. They've been in use for more than 60 years in products such as stain-proof textiles, waterproof clothing, some food packaging, paints, and lubricants, and are known to contaminate drinking water in the U.S. near various production facilities.

"We knew that small amounts of PFAS can occur in breast milk, but our serial blood analyses now show a buildup in the infants, the longer they are breastfed," researcher Philippe Grandjean said in a statement.

For the study, researchers collected and analyzed data from 81 children who were born in the Faroe Islands between the years 1997 and 2000. They looked at five types of PFASs in their blood at birth and ages 11 months, 18 months, and 5 years. They also looked at PFAS levels in mothers of the children at week 32 of pregnancy.

They found that, in children who were exclusively breastfed, PFAS concentrations in the blood increased by roughly 20 to 30 percent each month, with lower increases among children who were partially breastfed, UPI reported. In some cases, by the end of breastfeeding, children's serum concentration levels of PFASs exceeded that of their mothers', Medical News Today reported.

"There is no reason to discourage breastfeeding, but we are concerned that these pollutants are transferred to the next generation at a very vulnerable age. Unfortunately, the current U.S. legislation does not require any testing of chemical substances like PFASs for their transfer to babies and any related adverse effects," Grandjean said.

The findings are detailed in the journal Environmental Science & Technology.