Cadmium: Health Risks and Most Contaminated Foods
Cadmium is a metallic element best known for its high toxicity and carcinogenicity. Like all heavy metals, it accumulates in the bodies of most organisms (including humans). Alongside the three other heavy metals – arsenic, lead and mercury – cadmium appears in the WHO’s list of ten chemicals of major public health concern.
For many years, non-ferrous metallurgy, electroplating in the steel industry, manufacturing of nickel-cadmium batteries and burning of fossil fuels and municipal waste have been the prime sources of cadmium pollution. Today, cadmium is still used in the production of industrial pigments, PVC (though cadmium stabilizers were already phased out in the European Union) and cadmium telluride solar panels. Processing scrap steel is becoming a less important source of cadmium pollution. In addition, volcanic activity also releases substantial amounts of cadmium into the environment.
Occupational exposure is the most frequent cause of cadmium poisoning. In some parts of the world, industrial waste, airborne dust and fumes, and polluted drinking water that contain high concentrations of cadmium are still the main sources of concern for general population. However, for most others, food and tobacco smoke are the main sources of cadmium exposure. Cadmium is more readily absorbed by inhalation (5-50%) than ingestion (1-10%).
Health Hazards of Cadmium
Regardless of the type of cadmium compound or the route of absorption, cadmium is highly toxic and carcinogenic for humans. Although the kidneys and liver can transform most cadmium that enters the body into a form that is not harmful, too much overload may cause toxicity. Short-term exposure to cadmium causes respiratory irritation (when inhaled), especially irritation of the lungs and, when ingested, irritation of the stomach. The symptoms of acute cadmium poisoning may resemble a flu-like illness with fever, headache, coughing and chills. If cadmium entered the body through food or water, vomiting, stomach pain and diarhea may also occur.
Cadmium builds up in the kidneys (and to a lesser extent in the liver and muscles) and is, therefore, particularly toxic for the kidneys. It also causes release of calcium from the bones, oxidative stress and is mutagenic for human cells. Recent research suggests that cadmium could also act as an endocrine disruptor. As a result of all this, long-term exposure to cadmium has been associated with kidney and lung damage, lung cancer (perhaps also prostate, testicular and breast cancer), bone damage, liver disease, damage to the immune system, contact dermatitis, hormonal imbalances, metabolic disruptions, fetal malformations, decreased birth weight, impaired neurological development of young children, brain damage, psychological disorders and genetic mutations that can be passed along to future generations. It should be noted that some of these effects have only been observed in animal studies not humans.
Foods Most Contaminated with Cadmium
For non-smokers and people who are not occupationally exposed to cadmium, food is the main source of cadmium exposure. However, heavy smokers can absorb as much cadmium from tobacco smoke as they do from food.
Cadmium readily accumulates in aquatic organisms such as molluscs (snails, mussels, oysters, scallops, octopuses, squids and chitons), crustaceans (lobsters, shrimp, crabs, crayfish, prawns, krill) and fish and in agricultural plants including tobacco, leafy vegetables (e.g., broccoli, lettuce, spinach), soybeans, peanuts, grains (including rice), sunflower seeds, potatoes, starchy roots and cocoa beans. The use of phosphate fertilizers contributes to increased levels of cadmium in plants. In addition, cadmium uptake by plants is higher in acidified soil. Other foods high in cadmium are liver, mushrooms and dried seaweed. Contamination of drinking water with cadmium is for most people in the world a much smaller health concern than contamination of foods.
Paradoxically, many of the foods that are on the list of health foods of most dieticians, such as seafood, broccoli, soybeans or cocoa, also happen to be among those most contaminated with cadmium. In fact, seafood is not only high in arsenic and mercury. For some populations, it is also the chief source of cadmium exposure.
Where to Get More Information: International Cadmium Association