A number of toxic metals including arsenic and lead have been detected in widely used tampons that could increase the risk of adverse health effects among users, a new study by the University of California, Berkeley has found.

Researchers purchased tampons from September 2022 to March 2023 from stores in New York City, Athens, and London and from two popular online retailers. They tested 30 tampons—made from cotton, rayon, viscose, or a mix of these materials—across 14 brands and 18 product lines, and found all 16 types of metal they were testing for in every product.

“To our knowledge, our study is the first to assess concentrations of metals in tampons, despite the potential for substantial vaginal absorption of metals and the widespread and frequent use of tampons among menstruators,” the study’s authors wrote.

An estimated 52 to 86% of Americans who menstruate use tampons. There is no “safe” level for any of the metals researchers tested for, the study said.

Toxic metals are particularly dangerous if they come into direct contact with the vagina, where they are more easily absorbed. Chronic metal absorption has been linked to increased risk of dementia, cancer, infertility, and other health issues.

The level of metal detected in each tampon varied according to whether they were sold in the U.S., U.K., or E.U. There was also variance in metal levels depending on whether the tampons were organic or non-organic.

The authors wrote that some metals may be more “more abundant” in organic cotton tampons due to the use of fertilizers prevalent in the soil of organic cotton fields.

Tampons are regulated for product safety across the U.S., U.K., and the E.U., but existing rules do not require chemical testing in these jurisdictions.

The study notes that further research is needed to replicate its findings. The researchers also acknowledged some limitations of the study, including that absorption of metals was not tested and “thus we cannot estimate health risks (if any) from tampon use.”

“I really hope that manufacturers are required to test their products for metals, especially for toxic metals,” Jenni Shearston, the study’s lead author told Sky News.