Now we have one more reason to believe that ghar ka khaana (home-cooked meals) is better than fast food: A new study of fast food packaging has found it contains toxic chemicals known as PFAS.

PFAS stands for per- and polyfluoroalkyl substances and refers to a group of chemicals that are used to make packaging materials and other household items waterproof and fire-resistant. The chemicals are also grease-resistant, making them useful in packaging to transport and deliver food.

The study, published in Environmental Health Perspectives, aimed at assessing the levels of PFAS in people who ate fast food. It found an increase in the amount of PFAS in their blood after they had consumed fast food.

PFAS, said scientists of the study, can linger in the human body for years and is a risk factor for cancer, thyroid disorders, hormonal changes, and weight gain. Therefore, regular fast food consumption could mean a build-up of PFAS in the body.

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The harmful effects of PFAS are not limited to the consumption of food or the wearing of clothing packaged in it; per the study, PFAS can leach into groundwater when it accumulates in unlined landfills, too. In India, a 2016 study found 15 PFAS in Ganges River surface water in several locations; other studies have found PFAS contamination in fish and pigs. Particulate air pollution in India also contains PFAS particles, found another study.

In order to avoid the impact of PFAS, very recently, Denmark became the first country to ban it from food packaging, while the U.S. states of Washington, New York and Rhode Island, as well as the city of San Francisco, have each proposed restrictions of PFAS. However, in India, no PFAS substances are regulated, even after the country became a party to the Stockholm Convention in 2006, which designated the substances on its global restriction list.

Researchers in the latest study of food packaging assessed blood samples of more than 10,000 people from 2003 and 2014 and found five commonly used types of PFAS in at least 70% of participants. The survey also questioned people on how often they had eaten fast food over the past 24 hours, one week, and one month. Even after a 24-hour period, blood samples of those who had consumed fast food consistently showed an increase in the amount of PFAS proving that it stays in the body.

“We’re still learning about health effects that may occur at lower and lower levels of exposure,” study author Laurel Schaider, an environmental engineer and chemist at the Silent Spring Institute, said in a press release. “Food is just one source of exposure.”

PFAS is also commonly found in paint, carpeting, and clothing, she said. “At this point, I would say it makes sense for people to try to reduce their exposure, [but] we’re not able to link a certain rate of fast food intake with harmful health effects,” Schaider added.