The researchers collected toilet paper rolls sold in Africa, North America, Latin America, and Western Europe, along with sewage samples from wastewater treatment plants in the United States.
The paper was found to contain disubstituted polyfluoroalkyl phosphates" - or diPAPs - compounds that can convert to more stable PFAS such as perfluorooctanoic acid, which is potentially carcinogenic.
The research study published in the Environmental Science and Technology Letters journal found that toilet paper contributed about four percent of diPAPs in the United States and Canada, 35 percent in Sweden and up to 89 percent in France.
The numbers may be lower in North America because other products are responsible for PFAS in wastewater, such as cosmetics, textiles or food packaging.
"Forever chemicals", or PFAS, have been linked to several types of cancers, cardiovascular disease, fertility problems and developmental disorders in children.
The synthetic chemicals are present in soil and waterways across the globe, and the new study found that toilet paper "should be considered as a potentially major source" of PFAS in wastewater treatment systems.
The researchers said reducing PFAS in wastewater is "critical", since the chemicals are potentially harmful.
"Wastewater effluent and sludge are commonly reused for irrigation and/or land application; research has already shown that these two pathways pose a risk for human and environmental exposure to PFAS," said the study.
Introduced in the 1940s, PFAS (perfluorinated and polyfluorinated alkyl substances) are known as "forever chemicals" because they are extremely persistent in the environment and in our bodies.
Although hard to avoid entirely, contact with them can be reduced by avoiding non-stick cookware, stain-repellent and water-repellent materials and with proper water filtration.