Young children have a habit of putting things in their mouths, since sensory exploration is natural to learning. But mouthing certain items, such as inexpensive toy jewelry imported from China, may expose children to over 100 times the recommended limit of cadmium, a toxic metal.

A known carcinogen, cadmium is potentially harmful even at low doses, and has been linked to kidney, bone and liver disease.

The US Consumer Product Safety Commission (CPSC) has issued five recalls of children’s jewelry products for cadmium contamination. However, there is no formal standard for acceptable levels of cadmium in jewelry and few data exist regarding potential exposures.

The prevalence of cadmium in toy jewelry comes as a result of regulations banning lead from children’s toys. Cadmium is being used as a lead substitute, and its use in the marketplace is not yet regulated for children’s toys and jewelry. The CPSC has released guidelines on safe levels of the metal, but there is no way to enforce these recommendations at this time.

Of the 92 pieces of cadmium-containing jewelry tested in the study, which was published recently in the journal Environmental Health Perspectives, two would expose children to 100 times the recommended limit on cadmium had they been swallowed. And when the jewelry becomes scratched or damaged, as is often the case among anything a child wears or plays with regularly, the risk for exposure is even higher. The research found that damaged pieces of jewelry in some cases leached up to 30 times more cadmium than undamaged pieces.

Cadmium poses a special risk, said lead study author Jeff Weidenhamer, a professor of chemistry at Ashland University, because it’s impossible for parents to tell which items they buy contain the metal. Many don’t contain cadmium, he said, and among those that do, often the levels are ostensibly safe but can still be quite toxic.

Cadmium is also of major concern because it accumulates in the body over the course of a lifetime, Weidenhamer said. “And the digestive systems of kids are more efficient at absorbing cadmium, so exposure to kids who swallow these items is of increased concern.”

“Our hope is that the potential hazards of cadmium laden jewelry will be taken seriously,” says Weidenhamer. “While the bioavailability of cadmium from many items was low, the amounts of cadmium obtained from other items were extraordinarily high and clearly dangerous if these items were mouthed or swallowed by children. To think there are products on the shelf that you could pull thousands of micrograms of cadmium off by simple extractions like this is very concerning.”

“I like to tell people to buy books, avoid cheap costume jewelry and gumball machine jewelry, and try to keep toys and other products out of their children’s mouths. There are so many kids toys manufactured in other countries so it is hard to say don’t buy those, but I would be careful buying those,” said Dr. Adam Spanier, at the department of Pediatrics at Hershey Medical Center.

What’s more, the research on cadmium toxicity is still growing, said Bruce Fowler, cadmium specialist and toxicologist from the Centers for Disease Control and Prevention, and researchers have increasingly been lowering the threshold at which this metal can be harmful.

“It’s a moving target because the more sensitive tests we develop, the more we realize that even lower levels are toxic,” he said.

Cadmium contamination is a global health concern. Most human exposure comes from food or tobacco grown with cadmium-rich phosphate fertilizer. Health effects typically are not acute but instead result from chronic, long-term exposure. Because cadmium can accumulate in the body, all exposures should be avoided. Agencies around the world, including the World Health Organization, are working to regulate the use and disposal of the heavy metal.