What is Cadmium?

It’s a rare metal that does not occur naturally in nature. It comes from greenockite, which is nearly always is found in association with sulphide ores of zinc (sphalerite). Cadmium itself is a “transition metal” because it emerges as a by-product of zinc mining. It’s described as soft, bluish, and “easily cut with a knife.” As Audiologists, we were particularly taken with what’s described as the “cadmium scream” that occurs when you bend a bar of the metal.

What’s the Problem with Cadmium?
cadmium hearing aids

Cadmium is composed of several radioactive isotopes. It’s toxicity is such that it is highly regulated throughout the globe. It, and compounds containing cadmium, are known carcinogens. US and UK maximum safe levels of airborne cadmium intake averaged over 8 hours are 5 mg/cm3 air (OSHA, Permissible Exposure Level) and .025 mg/cm3 (HSE, Workplace Exposure Levels). Noting the wide difference in these two standards, I have to assume I’m missing something important here, and I invite readers with a better understanding of toxicity and standards to help set me straight. About 25K tons of cadmium enter the environment on an annual basis, half of it from manufacturing processes, the other half from nature. In short, it’s an occupational hazard but also an unavoidable part of everyday life.

What are the Natural Paths of Cadmium Exposure?

They’re not really “natural” but they are environmental . People are exposed to cadmium through cigarette smoke, food, and soils treated with artificial phosphate fertilizers. As I understand it, food does not naturally contain cadmium, but absorbs it from the soil during the growing process; likewise, water sources can contain cadmium from fertilized soil run off (see more in section after next). These sources of environmental contamination are recognized and controlled by government policy.

What Manufacturing Processes Use Cadmium?

Unfortunately–and the reason it’s globally regulated– is that it’s common to diverse industrial processes (e.g., manufacturing of nickel cadmium batteries, pigments, plastics and other synthetics). Other industrial uses include:

  • Electroplating and silver soldering
  • A barrier against nuclear fission
  • Black & white and blue & green phosphors for televisions
  • Paints, leather and textiles
  • Plastics stabilizer (e.g., PVC)
How Does Cadmium Get Into Our Bodies and Where Does it Go?

For those of us who don’t smoke cigarettes or work in industrial settings, our greatest everyday exposure to cadmium comes through food absorption. About half of the 25,000 tons of cadmium released into the environment every year comes from natural sources: weathering rocks release into streams; forest fires, volcanoes, and burning of fossil fuels release cadmium into the air. Then there’s the cadmium that gets into farm soils and water run-off from artificial phosphate fertilizers. All together, these sources get into plant life, and enters our mouths when that plant life is eaten. From there, it enters the bloodstream and travels to the liver and kidneys where it accumulates with a half-life of 10 to 50 years and can cause severe kidney damage or failure.

Cadmium can also enter the body by dust inhalation in industrial settings or through inhalation of cigarette smoke. In those cases, it settles in the lungs. long term exposure can cause inflammation and/or pulmonary edema, and other lung conditions.

As you’d expect, the toxicity risk of cadmium depends on type and amount of exposure.

Cadmium Has One Endearing Quality… at Least to Audiologists

No doubt, cadmium is not something you want to avoid in any form. But we did find one intriguing auditory characteristic of this element. It turns out that cadmium bars let out a characteristic “cadmium scream” when you bend them. We have not done that and remain content to take the word of those who bend cadmium. I hoped this cool video would do that, but even the expert doesn’t want to touch those bars!

Does cadmium scream in the forest if there’s no one to hear it? We’ll never know but it’s a unique characteristic, though. Does anyone know of other minerals that can be identified by their “utterances”?

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