Two new studies raise concerns about levels of mercury found in products containing high-fructose corn syrup.

In one study, published in Environmental Health scientists found mercury in nine out of 20 samples of high-fructose corn syrup tested.

Former FDA scientist and lead researcher Renee Dufault said she warned the agency about her findings, but they did not follow up, Reuters reports.

Meanwhile, a second study conducted by researchers at the Institute for Agriculture and Trade Policy sought to further investigate the results by testing products that contain high-fructose corn syrup.

Dr. David Wallinga and colleagues chose 55 commonly sold items that listed the ingredient first or second on its label.

“We found about one out of three had mercury above the detection limit,” he told Reuters.

The researchers suggest the food was exposed to mercury-contaminated caustic soda during the manufacturing process.

In response to the findings, the Corn Refiners Association said the study was based on outdated samples and the industry has used mercury-free versions of caustic soda “for several years.”

Those who prefer natural health resources may want to steer clear of products containing high-fructose corn syrup to limit their exposure to mercury.