The U.S. Food and Drug Administration (FDA) is investigating toxic metals found in tampons after lawmakers raised safety concerns, senator Patty Murray announced on Thursday.

Sen. Murray said that the FDA initiated an independent review of the literature on the metals’ health effects in response to a letter she sent in July, which urged the FDA to examine the findings of a recent study concerning the heavy metals in tampons.

Theepochtimes.com reports: That study, published in the science journal Environmental International in August, found measurable concentrations of 16 metals—such as lead and arsenic—in tampon products made by 14 common brands.

“These are products millions of women are using on any given day, so it’s important we absolutely put to rest any concerns about their safety,” Murray said in a statement on Sept. 5.

Murray said the FDA has commissioned an independent contractor to undertake the literature review to assess any possible links between tampon use and adverse health effects.

The agency also initiated an internal lab study to determine the amount of metals that may be released by the products during normal use, the senator added.

More than half of Americans who menstruate use tampons. Women may use more than 7,400 tampons in their reproductive years, according to the study conducted by researchers from the University of California Berkeley, Columbia University, and Michigan State University.

The researchers said that more studies are needed to replicate their findings and determine whether metals can leach out of tampons and be absorbed into the bloodstream through the vaginal lining.

“To our knowledge, this is the first paper to measure metals in tampons,” lead author Jenni A. Shearston said in a statement. “Concerningly, we found concentrations of all metals we tested for, including toxic metals like arsenic and lead.”

The metal concentrations varied depending on whether the tampons were organic or non-organic. Lead was detected in all 30 tampons tested in the study, and there is no safe level of exposure to this metal.

Exposure to heavy metals can potentially lead to health issues such as diabetes and cancer.

“Although toxic metals are ubiquitous and we are exposed to low levels at any given time, our study clearly shows that metals are also present in menstrual products, and that women might be at higher risk for exposure using these products,” Kathrin Schilling, one of the study’s co-authors, said in a statement.

UC Berkeley said in a statement that it was unclear if metals detected in the study could contribute to any negative health effects and that future research will test “how much of these metals can leach out of the tampons and be absorbed by the body; as well as measuring the presence of other chemicals in tampons.”

The FDA did not respond to a request for comment by publication time.