Is cadmium the new lead? Link reported between the ubiquitous metal and kids with learning disabilities.
By Marla Cone
Editor in Chief
Environmental Health News
February 10, 2012
It’s a heavy metal. It’s linked to learning problems in school children. And every child is exposed.
Sounds like lead?
Signs are emerging that cadmium – a widespread contaminant that gets little attention from health experts and regulators – could be the new lead.
Children with higher cadmium levels are three times more likely to have learning disabilities and participate in special education, according to a new study led by Harvard University researchers.
Absorbed from the soil, cadmium is found in certain foods, particularly potatoes, grains, sunflower seeds and leafy greens, as well as tobacco. It also has been discovered in some inexpensive children’s jewelry, prompting new voluntary industry standards last fall.
Dr. Robert Wright, the study’s senior author, emphasized that the links to learning disabilities and special education were found at commonplace levels previously thought to be benign.
“One of the important points of the study is that we didn’t study a population of kids who had very high exposures. We studied a population representative of the U.S. That we found any [effect] suggests this is occurring at relatively low levels,” said Wright, an associate professor of pediatrics and environmental health at Harvard.
Scientists said the new findings are a sign that cadmium could have dangerous properties similar to lead that alter the way children’s brains develop. More research is necessary, though, to confirm and refine the potential effects on kids.
“It does certainly point to the fact that we need more attention paid to the neurotoxic effects of cadmium in children," Wright said.
Until now, the nervous system has not received much attention as a target for cadmium. Some studies of adult workers, however, have shown that high exposures can trigger neurological problems, and small, earlier studies of children found links to mental retardation and decreased IQs.
The new study is the largest to look at connections between cadmium in urine and neurological effects, and the only one that has used a national group of children.
“Collectively, the studies are very consistent. They provide fairly substantial support that cadmium is a neurotoxin,” said Dr. Bruce Lanphear, a pediatrician and epidemiologist at Simon Fraser University who was a co-author of the study.
Lanphear, one of the world’s leading experts on the effects of lead in children, added that “the pattern we’re seeing here with cadmium is very consistent with what we see with other toxicants,” including lead and mercury.
The two scientists recommended that government re-examine its standards and guidelines for cadmium in food, soil, workplaces and consumer products to consider the effects on children’s brains.
Current regulations for cadmium are based on threats to adults, and the kidneys have been considered the most sensitive organ to its toxic effects. Classified as a known human carcinogen, it is linked to lung, kidney and prostate cancer in workers.
“We’ve got a large new national study showing a threefold increase [in children’s learning disabilities and special education]. But I wouldn’t go so far to say we definitely need to lower regulatory levels. It deserves to be re-evaluated, though,” said Lanphear.
Of the 2,199 children between the ages of 6 and 15 included in the new study, 12.6 percent had a learning disability and 10.5 percent were enrolled in special education classes, according to the study, published online in Environmental Health Perspectives last month. The children were not tested for disabilities; instead it was reported by their parents on a questionnaire that is part of the National Health and Nutrition Examination Study.
For those with the highest cadmium levels, the odds of having a learning disability were 3.21 times higher than for the children with the lowest exposures. For special education, the odds were 3 times higher. No association was found with attention deficit hyperactivity disorders.
“The three times higher risk is high for such low cadmium levels,” said Aimin Chen, an assistant professor of environmental health at University of Cincinnati’s College of Medicine. He was not associated with the study.
But Chen said the link at this point is preliminary because researchers have not yet looked for any specific, more definitive neurological effects, such as reduced IQs, memories or vocabularies -- outcomes already linked to two other toxic metals, lead and mercury.
The connection to both learning disabilities and special education could indicate cadmium has an array of effects on a child’s brain just like lead does. Those two outcomes “are actually a mixture of different brain function problems,” Chen said.
Lead has been studied and regulated for many decades, leading to a large amount of evidence that it reduces children's IQs at low concentrations and contributes to attention disorders and even violent behaviors. It interferes with the development of synopses, or connections between neurons, that allow a child to learn.
Since cadmium is also a heavy metal, it might have similar effects on the brain, Lanphear and Wright said. But unlike lead, cadmium “is relatively understudied as respect to brain toxicity,” Wright said.
One big difference turned up in the new study: No link was found between cadmium and attention deficit disorders. “It stands out because one thing we’ve found fairly consistently with lead, tobacco and others is that it seems that some of these contaminants might increase the risk for ADHD,” Lanphear said. That could be a sign that cadmium is working on a different part of the brain, not the prefrontal cortex.
Another big mystery is the source of the cadmium in the kids. Cadmium stays in the body for long periods, so the tests measured amounts the children were exposed to over years.
Cadmium is in tobacco smoke, but surprisingly, concentrations in the kids were similar whether they lived with smokers or not. That “might mean for most kids [secondhand] smoking was not a major source,” Wright said.
An abundant element in the Earth’s crust, cadmium is found naturally in soil in some parts of the country. But it also is released by battery manufacturers, smelters, electroplating plants and other industries. It is one of the top chemicals reported in Superfund sites, found in virtually all of them, according to a Centers for Disease Control and Prevention document.
Some crops, including tobacco plants and leafy greens, easily absorb cadmium from the soil. Hot spots in ground water include California’s Salinas Valley, where most of the nation’s lettuce and spinach is grown. [Editor's note: Location corrected 8/25/2013]
Renee Gardner, a postdoctoral fellow at Sweden's Karolinska Institutet who studies heavy metals, said “the most important source of exposure is food. Green leafy vegetables and grains are the biggest sources, though most plant foods have some cadmium in them.”
Since these foods are important nutritionally, they shouldn’t be avoided. But Gardner said that iron helps prevent absorption of cadmium, so parents worried about exposure should ensure their kids have adequate iron in their foods.
Some children may have been exposed through inexpensive jewelry. In 2010, the Associated Press tested children’s jewelry manufactured in China and found cadmium, prompting recalls by stores. Cadmium was being used to replace lead.
Last fall, the Consumer Product Safety Commission considered standards, but backed off when the industry set its own voluntary testing procedures and limits for cadmium in children’s jewelry. California set its own standards.
Lanphear said for most children, jewelry probably isn’t responsible for the cadmium in their bodies. “But for some kids, those kids that swallow it, it’s an extraordinarily important source,” he said. It also can enter the body by mouthing the jewelry.
Saying the voluntary standards don’t go far enough, Wright recommended that cadmium be removed from all jewelry and other children’s products.
“It's very concerning to me that cadmium can be found in a children’s product,” Wright said. “Even if one child in a million is exposed that’s one child too many.”
The jewelry is an example of how one dangerous substance often replaces another, Lanphear said.
“Perhaps the biggest failure is to fail to learn the lesson of the lead pandemic, that environmental chemicals and metals have the potential to be toxic, so in the end they shouldn’t be treated any differently than drugs. They shouldn’t be used unless proven safe,” he said.
Is cadmium the new lead? Link reported between the ubiquitous metal and kids with learning disabilities, by Environmental Health News is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.
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