91: Cadmium

HISTORY AND EPIDEMIOLOGY

Cadmium, atomic number 48, is a transition metal in group IIB of the periodic table. In its pure atomic form, it is a bluish solid at room temperature. It is readily oxidized to a divalent ion, Cd²⁺. Naturally occurring cadmium commonly exists as cadmium sulfide (CdS), a trace contaminant of zinc-containing ores.³⁶

Cadmium sulfide, cadmium oxide, and other cadmium-containing compounds are refined to produce elemental cadmium, which is used for industrial purposes. When combined with other metals, cadmium forms alloys of relatively low melting points, which accounts for its extensive use in solders and brazing rods. Today, cadmium is primarily used as a reagent in electroplating and in the production of nickel-cadmium batteries. Other uses of cadmium include as a pigment and as a neutron absorber in nuclear reactors. Cadmium salts have also been used as veterinary antihelminthics.¹²

As cadmium processing has increased, so has the incidence of cadmium toxicity. Cadmium toxicity usually occurs after environmental, occupational, or hobby work exposure.

Environmental Exposure

Environmental exposure to cadmium generally occurs through the consumption of foods grown in cadmium contaminated areas. Because cadmium is fairly common as an impurity in ores, areas where mining or refining of ores takes place are the most likely to contain cadmium contamination.

In the 1950s, a mine near the Jinzu River basin in Japan discharged large amounts of cadmium into the environment, contaminating the rice that was a staple of the local food supply. An epidemic of painful osteomalacia followed, affecting hundreds of people, with postmenopausal multiparous women being most affected.⁶⁷ The afflicted were prone to develop pathologic fractures, and were reported to call out “itai-itai” (“ouch-ouch”) as they walked, because of the severity of their pain.²⁸ These symptoms were ultimately linked to the cadmium. Less consequential environmental cadmium exposures have also occurred in Sweden,⁴⁶ Belgium,¹⁰ and China.⁴⁸ Additionally, smokers have higher blood cadmium concentrations than nonsmokers,⁹¹ probably as a result of contamination of soil where the tobacco is grown. This is noteworthy, in that cadmium and tobacco may be synergistic causes of chronic pulmonary disease.⁶³

Occupational and Hobby Exposure

Welders, solderers, and jewelry workers who use cadmium-containing alloys are at risk for developing acute cadmium toxicity due to inhalation of cadmium oxide fumes. Other workers who do not work with metals per se may develop significant chronic cadmium toxicity through exposure to cadmium-containing dust.

Hobbyists who work with cadmium solders have exposures similar to occupational metalworkers. Significant cadmium toxicity in this population is usually the result of metalworking in a closed space with inadequate ventilation and or improper respiratory precautions.

TOXICOKINETICS

There is no known biologic role for cadmium or its salts. Orally ingested cadmium salts are poorly ...