A widely used class of industrial chemicals linked to cancer and immune system problems accumulates in the bodies of infants by 20 to 30 percent for each month they're breast-fed, a new Harvard University study warns.

This is the first study to show that perfluorinated alkylate substances, or PFASs are transferred to babies through breast milk, the researchers said.

The study involved 81 children living in the Faroe Islands, which is halfway between Iceland and Norway, whose blood levels of the chemical were measured at regular intervals.

"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," said Philippe Grandjean, M.D., adjunct professor at the Harvard School of Public Health, who co-authored the study, which is published in the journal Environmental Science & Technology.

The study shouldn’t dissuade women from breast-feeding, scientists said, because the health benefits to both mother and child have been well demonstrated.

However, the findings warrant more tests to find if the chemical is widespread in infants, they said.

PFASs, which make products stain-resistant, have been found to contaminate drinking water near U.S. production facilities and also to accumulate in the food chain.