Many common foods made using commercial high fructose corn syrup contain mercury as well, researchers reported on Tuesday, while another study suggested the corn syrup itself is contaminated.
Food processors and the corn syrup industry group attacked the findings as flawed and outdated, but the researchers said it was important for people to know about any potential sources of the toxic metal in their food.
In one study, published in the journal Environmental Health, former Food and Drug Administration scientist Renee Dufault and colleagues tested 20 samples of high fructose corn syrup and found detectable mercury in nine of the 20 samples.
Dufault said in a statement that she told the FDA about her findings but the agency did not follow up.
Dr. David Wallinga, a food safety researcher and activist at the nonprofit Institute for Agriculture and Trade Policy, said he followed up on the report to find mercury in actual food.
"When I learned of that work, I said that is interesting but we don't just go out and eat a spoonful of high fructose corn syrup," Wallinga said in a telephone interview.
"We went and looked at supermarket samples where high fructose corn syrup was the first or second ingredient on the label," he said. These 55 different foods included barbecue sauce, jam, yogurt and chocolate syrup.
"We found about one out of three had mercury above the detection limit," Wallinga said.
The Corn Refiners Association challenged the findings.
"This study appears to be based on outdated information of dubious significance," the group said in a statement.
Wallinga and colleagues said they believed the mercury got into the food during manufacture, at plants that use mercury-grade caustic soda produced in industrial chlorine plants, although his team was unable to show this.
"Our industry has used mercury-free versions of the two reagents mentioned in the study, hydrochloric acid and caustic soda, for several years," Audrae Erickson, president of the Corn Refiners Association, said in a statement.
Wallinga said the studies were based on samples taken in 2005, the most recent available.
Many studies have shown that fish can be high in mercury. Wallinga said consumers should know about other potential sources so they can limit how much they eat. "The best mercury exposure is no exposure at all," he said.
"Even at low levels methylmercury can harm the developing brain. The last thing we should intentionally do is add to it," Wallinga added.
He said his team did not test foods that did not contain corn syrup to see if they were also high in mercury.