According to a new study in the Journal of Exposure Science and Environmental Epidemiology, fast food from popular chains such as McDonald’s, Burger King and Pizza Hut contain harmful chemicals linked to a suite of health problems.

As Americans devour a fast-food burger in the car or gobble up a chicken burrito in front of the TV, some may bite into phthalates, according to a new study in the Journal of Exposure Science and Environmental Epidemiology.

This is the first study to directly measure the amount of phthalates present in common fast foods in the U.S. and adds to mounting evidence linking phthalate exposure to fast food consumption.

A group of synthetic chemicals widely used to make plastic more flexible, phthalates are as ubiquitous in modern life as their host plastic products, ranging from toys to personal care products to food packages.

Easily absorbed by human bodies, phthalates have been shown in human and animal studies to disrupt our endocrine system by heisting hormone receptors — such as the estrogen receptors or the retinoic acid X receptors — and turning on and off the switches for gene expressions.

The chemicals have been linked to a wide range of health impacts, including birth and reproduction problems, impaired brain development, diabetes and cancer.