Cadmium: The Highly Toxic Metal That Powers the World

Cadmium is a natural metal, like silver or platinum, found in nature, usually in zinc ores. It is a chemical element with the symbol Cd and atomic number 48 and is chemically similar to the two other stable metals in Group 12 of the periodic table, zinc and mercury. It's soft, silvery-white in color with a bluish tint that diminishes when exposed to air or moisture.

"This rare metal is also ductile and malleable, which means that you can easily shape it. It is resistant to corrosion and has a lower melting point than most other transition metals," says Samir Jaber, a technical content writer and editor at Matmatch GmbH, a materials science-based platform for material and supplier sourcing based in Munich, Germany.

Because cadmium has a low melting point of 609 degrees Fahrenheit (321 degrees Celsius) and is corrosion resistant, it's a popular choice for coating steel for industrial purposes. (Rhodium, by contrast, has a high melting point, at 3,595 degrees F, or 2,035 degrees C). It's also an efficient energy conductor. However, there are different types of cadmium and so its characteristics may differ depending on the supplier and material grades, notes Jaber. It's used to stabilize paint pigments ranging from yellow to maroon, steel coating, batteries, solar power and barrier material in nuclear fission reactors. "However, cadmium is quite toxic to humans upon exposure and does not have a taste or odor," Jaber says.

Cadmium is released into the atmosphere in two main ways: through natural events like the weathering of rocks, forest fires or volcanoes; or human activity like mining and manufacturing. "Cadmium exposure predominantly takes place in areas where cadmium-containing products are produced or recycled, such as zinc mining, cadmium coating of steels, nickel-cadmium battery production, and others. That happens by inhaling dust and fumes emanating during processes, such as smelting," explains Jaber.

Both natural and manufacturing processes are responsible for more than 10,000 tons (9,072 metric tons) of cadmium into the environment, where it can seep into water supplies and soil used to grow crops, ultimately ending up on your plate, which is how most of the general non-smoking population come into contact with toxic cadmium. Smokers can also add cadmium to the list of ways they harm themselves with each puff, as Cd is known to exist in high levels in tobacco plant leaves.

"Cadmium is highly toxic to humans. It has been found that exposure to cadmium may lead to cancer, and it can affect the body's systems, including the respiratory, cardiovascular, gastrointestinal, reproductive, renal, and neurological systems," says Jaber. "Lung damage, bone toxicity, and the itai itai disease are only a handful of examples of cadmium toxicity." You might be eating, drinking or inhaling cadmium without ever knowing it.

"People shouldn't be alarmed, but they should be well-informed about the existence and amount of cadmium in their surroundings," recommends Jaber. The Occupational Safety and Health Organization (OSHA) of the United States Department of Labor limits the use of cadmium across multiple industries, to reduce human exposure. The European Union also instituted the Batteries Directive, released in 2006, that limits the amount of cadmium, by weight, that can be present in batteries or accumulators — except those used in medical or emergency devices.

If visiting or working at a facility that handles cadmium, Jaber says you'll need to throw on some protective gear — and bonus points for those who stop smoking. "People can minimize the risk of cadmium exposure by using the proper personal protective equipment at workplaces that may include handling of cadmium," he says. "They can also protect themselves by reducing smoking or stopping it altogether, as the smoke can transfer cadmium through to be absorbed by the lungs." If you've been exposed to cadmium, it's probably not a bad idea to go see your doctor.

The most common use of cadmium is in nickel-cadmium (Ni-Cd) rechargeable batteries. They have a high energy density and long lifespan, which makes them popular for industrial uses.

More recently, Jaber says, cadmium is being used in the solar energy industry. "Cadmium is also gaining traction in the solar industry, as cadmium telluride (CdTe) solar cells have become the second-most common photovoltaic technology behind crystalline silicon," he says. "This is thanks to its high absorption with a near-optimal bandgap energy to convert radiation from the sun into electricity in a single junction."

Don't worry about handling toxic batteries or your solar-powered sidewalk lights, because cadmium is rarely found in household batteries or tools. Even if you do come across a battery with cadmium, proper disposal can eliminate any potential harm to you. "People should not be concerned, but it is important to know where and how to dispose of such batteries. In fact, Ni-Cd batteries can be recycled at specific recycling points, so they should be taken separately to a household hazardous waste disposal facility, given their hazardous nature," suggests Jaber.