Cadmium and cadmium compounds and cancer

ROC STATUS: Known human carcinogen since 2000

ALSO KNOWN AS: Cadmium chloride, cadmium sulfate, cadmium nitrate, cadmium oxide, cadmium sulfide, cadmium carbonate, greenockite, capsebon, cadmopur yellow

DEFINITION: Cadmium is a natural metal that usually occurs in combination with other elements rather than in its pure state. It is most frequently found in zinc deposits as cadmium sulfide. Commercial use of cadmium began at the end of the nineteenth century and became widespread by the middle of the twentieth century. The non-corrosive properties of cadmium led to its use in batteries, electroplating, and coating of other metals, such as steel. Workers are at risk for occupational exposure to cadmium through inhalation, but cadmium also may be released into the environment through these industrial processes. Additionally, cadmium is released into the environment from other sources, including forest fires, volcanoes, weathering of rocks, and combustion of fossil fuels such as coal. Both industrial and natural cadmium releases into the atmosphere put the general public at risk for exposure through contaminated water, air, and soil. Plants can absorb cadmium from contaminated soil, so the major exposure to cadmium in the general public is through the food supply. Tobacco plants are among those that absorb cadmium, so tobacco smoking is another source of exposure for the general public.

Related cancers: Lung cancer, possibly prostate and kidney cancer

Exposure routes: Inhalation and ingestion

Where found: Food (particularly grain cereal products, potatoes, and other vegetables), cigarette smoke, zinc and lead ores, electroplating and -coating, alloys, pigments (paint, glass, ceramics, porcelain, textiles, plastics, paper, and fireworks), stabilizers in plastics, nickel-cadmium batteries, smoke detectors, radiation detectors, and various electronics and laboratory equipment

At risk: Workers who refine and smelt zinc and lead ores, workers in industries using thermal processes (iron production or welding cadmium-coated steel), and tobacco smokers

Etiology and symptoms of associated cancers: Cadmium exposure can be acute or chronic. Acute toxicity through ingestion of cadmium may cause only short-term illness, but acute toxicity through inhalation can lead to severe damage to the lungs and even death. Chronic exposure to cadmium can cause damage to the lungs, kidneys, and sometimes bones. Studies have shown that inhalation of cadmium in the workplace is associated with lung cancer. Laboratory studies using cultured cells have shown that cadmium damages the deoxyribonucleic acid (DNA) of the cells and affects the cells' ability to repair DNA damage. These factors are likely to be the mechanism through which cadmium contributes to cancer formation in humans.

Lung cancer can affect one lung or both. Lung cancer detection often occurs when the disease has progressed to late stages because symptoms may take years to appear. When symptoms appear, they are often mistaken for other less serious conditions. Common signs and symptoms of lung cancer are persistent cough (not related to smoking); persistent pain in the chest, shoulder, or back; coughing up mucus or blood; recurrent respiratory infections; shortness of breath; fatigue; unexplained weight loss; and loss of appetite. Many of these symptoms may be attributed initially to other causes before lung cancer is eventually diagnosed. According to the National Toxicology Program's Report on Carcinogens, Twelfth Edition (2011), lung cancer is the only cancer that has been confirmed to be associated with cadmium exposure.

Studies from the 1960s and later have had conflicting results regarding a connection between cadmium and prostate cancer. Several studies have shown increases in the occurrence of prostate cancer in workers exposed to cadmium in nickel-cadmium battery plants and other industrial sites. Still, conflicting studies have indicated either no increases or increases that were too small to be statistically significant. Cadmium has also been implicated in kidney cancer, with early studies showing a correlation between exposure and increases in kidney cancer. However, further studies have not confirmed this association.

History: Industrial use of cadmium became widespread in the middle of the twentieth century, and the toxic effects of occupational exposure began to be recognized by the early 1950s. Studies that examined workers who had been exposed to high levels of cadmium were used to explore the toxic effects, and by the 1960s, researchers were investigating cadmium's potential carcinogenicity. Experimental animal studies were also conducted to research cadmium's toxicity and carcinogenicity. Regarding the role cadmium played in the development of lung cancer, initial studies were inconclusive or conflicting. Associated factors, such as workers who were tobacco smokers or were exposed to additional heavy metals, contributed to the confusing results. Because of its toxic effects, many federal, state, and local agencies, including the Environmental Protection Agency (EPA), began to regulate cadmium in various ways, including stipulating allowable amounts in air and water. In 1992 the Occupational Safety and Health Administration (OSHA) ruled on permissible exposure limits (PELs) for workers exposed to airborne cadmium in the workplace. By 2000, sufficient studies reported that cadmium contributed to the development of lung cancer for it to be designated as a known human carcinogen by the US Department of Health and Human Services.

In the 2010s,, certain products containing cadmium began to be banned in Europe. Items such as jewelry and artistry paint were subjected to this action. In 2015, cadmium was one of six banned substances named by the European Union's Directive on the Restriction of Hazardous Substances. Cadmium in certain plastics had already been prohibited for more than a decade. In 2015, following an uproar from the artist community, the cadmium ban on paint was lifted. Cadmium is not prohibited in the U.S., but it is regulated. In 2024, cadmium was named as one of four substances that must be tested in baby food sold in California. In addition, manufacturers must begin posting online results in 2025. This action was spurred by high levels of heavy metals that often appear in baby foods. Heavy metals consumed by young children can later result in cognitive impairment and behavioral and cardiovascular issues.

Bibliography

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