Cadmium is a toxic heavy metal and occurs naturally in the Earth’s crust. It stems from eroded rock or volcanic eruptions. Furthermore, anthropogenic sources also play a part in the entry of cadmium into the biosphere. Their causes include emissions from metal mining and smelting, industrial and agricultural waste, phosphate fertilisers, sewage sludge, the burning of coal as well as the use of batteries and alloys. The heavy metal thus finds its way into soil, sediment in bodies of water. In the environment cadmium rarely occurs as a pure metal, usually occurring instead as inorganic compounds such as cadmium chloride, bromide, sulphate, oxide and sulphite.
In mammals, birds and fish as well as in plants, cadmium is found bound to proteins. Crop plants may absorb cadmium from the soil to differing degrees. Various factors influence absorption, such as soil consistency, type of crop and different farming practices like the use of phosphate fertiliser or sewage sludge. Cadmium can also find its way into plant-based foodstuffs via atmospheric deposition.
The primary means of absorption in non-smokers is via food, which accounts for around 90%. The remaining exposure (10%) is accounted for by ambient air and by drinking water (EFSA, 2012). Oil-bearing seeds, cocoa beans, wild mushrooms, nuts, cereals, seaweed and some vegetables are among the plant-based foodstuffs with the highest cadmium contamination levels. Offal and seafood can also be contaminated with elevated levels of cadmium.
However, often it is not the foodstuffs with the highest cadmium content that make the greatest contribution to cadmium intake, but the foodstuffs that are consumed in the largest quantities and with the greatest frequency such as cereals and vegetables (EFSA, 2009).
Besides food, smoking is another source of exposure to cadmium.
Young children can also absorb cadmium orally via house dust or soil (EFSA, 2009).
Cadmium is an accumulative, toxic heavy metal with a biological half-life of 10 to 30 years. It accumulates in the food chain and in human organs, especially the liver and kidneys as well as in the bones. It is only excreted very slowly via the kidneys and gut.
Compared to men, women tend to have higher cadmium levels since they are more prone to iron deficiency. Women of child-bearing age often suffer from iron deficiency and pregnancy in particular can cause low levels.
Cadmium poisoning via inhalation may have fatal consequences, as a series of workplace accidents has proved. Acute oral poisoning via water and drinks with very high cadmium content in particular causes gastro-intestinal symptoms within minutes of consumption. The most sensitive target organ in long-term oral absorption of cadmium are the kidneys.
A total of over 4,000 samples from 67 different food categories were tested for cadmium. Cadmium is ubiquitous and is absorbed primarily via frequently consumed foods. Major sources of cadmium intake for the Austrian population are cereals, potatoes, chocolate and leaf vegetables. Foodstuffs that are heavily contaminated with cadmium are molluscs, mushrooms, cocoa products, chocolate and certain food supplements. Cadmium content in cereals and vegetables is not only location-dependent, but also dependent on species, variety and plant organ. In chocolate there is a correlation between the cadmium content and the cocoa content.
This risk assessment deals exclusively with oral cadmium intake from foodstuffs, however it should also be noted that cigarette-smoking makes a very high contribution to cadmium exposure.