Fourteen popular brands of tampons sold in the U.S. and UK have been found to contain dangerous levels of lead, arsenic and cadmium, according to reports.

Scientists at the University of California, Berkeley, and Columbia University confirmed on Thursday that 16 types of toxic metals were found in the 30 products tested by public health researchers.

Salon.com reports: “Despite this large potential for public health concern, very little research has been done to measure chemicals in tampons,” said lead study author Jenni A. Shearston, in a university statement. “To our knowledge, this is the first paper to measure metals in tampons. Concerningly, we found concentrations of all metals we tested for, including toxic metals like arsenic and lead.”

The list of metals discovered includes arsenic, barium, calcium, cadmium, cobalt, chromium, copper, iron, manganese, mercury, nickel, lead, selenium, strontium, vanadium and zinc. Concentrations of the metals varied by country of purchase, whether a product was store-brand or name-brand, and whether the product was labelled organic or non-organic. Non-organic tampons contained higher concentrations of arsenic and lower levels of lead, while organic tampons had more lead and less arsenic. Researchers said the metals could have entered the products in any number of ways and that further testing is needed — but made clear that no amount of lead exposure is considered safe for human reproductive health, and none of the brands tested were notably lower than others in metal concentration. 

“I really hope that manufacturers are required to test their products for metals, especially for toxic metals,” Shearston said in the statement. “It would be exciting to see the public call for this, or to ask for better labeling on tampons and other menstrual products.”

These findings follow a 2023 study from the University of Notre Dame which found polyfluoroalkyl chemicals — or PFAs, also known as “forever chemicals” — in 123 menstrual products sold in the U.S. Similarly, a 2022 consumer watchdog study reviewed by Carnegie Mellon University researchers found that, out of 23 tampon brands tested, 22% contained PFAs, as did 48% of tested pads and liners. California lawmakers have tried at least twice to ban PFA use in tampons sold in the state.