Children can be exposed to as much as 100 times the recommended limit of cadmium when they mouth or accidentally swallow inexpensive jewelry, toxicologists warn.

Canadian and U.S. product safety authorities are investigating the presence of cadmium in children's jewelry imported from China following an Associated Press investigation in January. It found some Chinese manufacturers have been substituting cadmium for lead in cheap charm bracelets and pendants being sold throughout the United States and possibly Canada.

Cadmium, a heavy metal, can cause kidney, bone, lung, and liver disease. Because cadmium can accumulate in the body, all exposures should be avoided, health authorities say.

Researchers tested 92 pieces of cadmium-containing jewelry, and found a football pendant and a heart charm, for example, would expose children to 100 times the recommended limit on cadmium had they been swallowed.

"These results indicate the potential for dangerous cadmium exposures to children who wear, mouth, or accidentally swallow high-cadmium jewelry items," the study's authors concluded in Friday's online issue of the journal Environmental Health Perspectives.

Scientists also did separate tests to mimic normal use by children that could scratch or damage the outer coating on the jewels.

In those cases, the risk of exposure grew. Six damaged charms in the shape of sandals yielded 30 times as much cadmium as undamaged charms.

The study's lead author, Jeffrey Weidenhamer, a chemistry professor at Ashland University in Ohio, said they hope the potential hazards of cadmium-laden jewelry will be taken seriously since the amounts of cadmium were "extraordinarily high and clearly dangerous if these items were mouthed or swallowed by children."

Cadmium is a particular concern because it accumulates in the body over our lifetime, the researchers said. Kids' digestive systems are also more efficient at absorbing cadmium, they noted.

It is impossible for parents to tell which items contain cadmium because it is not identified on the product.

The study tested cadmium-laden jewelry, mostly charms and necklace pendants labelled for children and imported mainly from China. Most sold for less than $5 each and were bought in 2009 and 2010.

Agencies around the world, including the World Health Organization, are working to regulate the use and disposal of the heavy metal.

The study was funded in part by a grant from the Dr. Scholl Foundation.