New York: While breast milk is regarded as the best source of nutrition for a newborn, researchers have now found that exclusive breastfeeding for a long time may also expose infants to a class of industrial chemicals linked with cancer and immune system dysfuntion.

The chemicals –perfluorinated alkylate substances, or PFASs – appear to build up in infants by 20-30 percent for each month they are breastfed, the findings showed.

“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,” said one of the researchers Philippe Grandjean, adjunct professor of environmental health at Harvard T.H. Chan School of Public Health in Boston, US.

“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,” Grandjean pointed out.

PFASs are used to make products resistant to water, grease, and stains. These compounds –which tend to bioaccumulate in food chains – are found regularly in the blood of animals and humans worldwide, and have been linked with reproductive toxicity, endocrine disruption, and immune system dysfunction.

For the study, the researchers followed 81 children who were born in the Faroe Islands between 1997-2000, looking at levels of five types of PFASs in their blood at birth and ages 11 months, 18 months, and five years.

In children who were exclusively breastfed, PFAS concentrations in the blood increased by roughly 20-30 percent each month, with lower increases among children who were partially breastfed.

After breastfeeding was stopped, concentrations of all of five types of PFASs decreased.

The study appeared online in the journal Environmental Science and Technology.