Cadmium has been used in a number of industrial processes and products, including in batteries and mining operations, and in rust protection for steel. Cadmium is transported both through sea and air, and it may pollute the marine environment via rivers. Cadmium emissions have been reduced by 95 per cent in Norway over the past 30 years.
In Europe, the most important dietary source of cadmium are grain products and vegetables. Fish absorb cadmium to a very limited extent, but it can accumulate in molluscs. In fish, it is accumulated in the kidneys and liver. Crabs and shellfish have a limited ability to excrete kadmium, which means it accumulates easily. Brown crab meat, horse mussel kidneys and the digestive gland of scallops are some examples of organs that contain a lot of cadmium.
Cadmium has a long half-life in humans and can be carcinogenic. It can accumulate in the kidneys and lead to kidney failure. Cadmium can also have an adverse effect on fertility.
The legal maximum level for cadmium in fish fillet is 0.05 mg/kg, while it is 0.5 mg/kg in crab claw meat. The tolerable weekly intake of cadmium is 2.5 µg cadmium per kg body weight per week, and the intake in Europe is roughly at this level. Agricultural products are the largest dietary cadmium source.
Maximum levels in fish feed
Cadmium in fish feed mainly comes from fishmeal. The maximum legal level for cadmium in fish feed has recently been increased from 0.5 to 1.0 mg/kg feed, but the results of the feed monitoring programme show that the average levels of cadmium in fish feed are well below the previous threshold value. Since cadmium to a very limited extent is transferred from feed to muscle tissue (2-6 per cent), most of it is discharged to the environment. We know little at present about the consequences of these emissions.