Occurrence in food
Nickel is a heavy metal occurring naturally in the environment. Nickel can also be released into the environment due to human activities, for example as a result of mining or metal processing, or as a result of burning fossil fuels. The amount of nickel released into the environment as a result of human activity is limited by environmental legislation. Nickel can end up in foods by being absorbed from the soil into the plant as it grows. Nickel does not accumulate much in animal tissues.
Human exposure to nickel is primarily through food. In food, Nickel usually occurs in its most stable form of oxidation, the divalent cation Ni (II). In foods, the highest levels of nickel have been found in legumes and pulses, nuts and oilseeds, as well as in cocoa beans and certain cocoa products. However, according to the EFSA's risk assessment, the main sources of nickel exposure in food are, because of their high use, cereals and cereal products, non-alcoholic beverages (excluding milk), sugar and confectionery (especially chocolate), legumes and pulses, nuts and oilseeds, and vegetables and plant products. In infants, milk and dairy products can also be a significant source of nickel exposure.
Nickel may migrate to food from food contact materials, including metal appliances and kitchen utensils.
Adverse health effects
Symptoms of immediate nickel poisoning include gastrointestinal irritation as well as nervous system symptoms. In addition, nickel allergy sufferers may present skin symptoms (contact dermatitis) especially from contact exposure, but also from dietary exposure. Prolonged exposure to nickel can damage the kidneys, liver and the function of the immune system. Foetal exposure to nickel can cause a delay in the development of the child.
The International Agency for Research on Cancer (IARC) has classified nickel as a human carcinogen in cases of inhalation exposure. In contrast, studies show that exposure through food is highly unlikely to cause cancer.
The European Food Safety Authority (EFSA) has set a maximum tolerable daily intake (TDI) for nickel of 2.8 µg/kg bw/d. The consumer can therefore consume a dose of this size every day of their life without suffering any health problems such as increased risk of miscarriage. Toxicological reference values for other adverse effects of long-term exposures to nickel are higher.
However, for nickel allergy sufferers, the acute exposure toxicological reference value (BMDL10, benchmark dose limit) has been set at 1.1 µg/kg bw/d. The BMDL10 value is defined as the average long-term exposure level at which the risk of the studied health hazard at the population level increases by one per cent of the risk level that the unexposed population would have. When the exposure of nickel allergy sufferers exceeds the BMDL10 value, the possibility of contact dermatitis, i.e. a rash-like skin reaction, cannot be ruled out. Symptoms may thus not yet occur at this dose, but their risk increases.
Maximum level in foods
At present, no maximum level has been set for nickel in food. However, food placed on the market in accordance with the General Food Law Regulation ((EC) No 178/2002 as amended) must always be safe for consumers.
In addition, Finland has a national decision 268/1992 (KTM), which sets a migration limit value of 2.0 mg/dm2 for all food contact materials. Migration from food contact materials intended for young children should only be 1/10 of this amount. The same regulation also sets limit values for cadmium, chromium and lead migrating from food contact materials.