EPA has classified nickel refinery dusts and nickel subsulfide as Group A, human carcinogens . Nickel carbonyl has been reported to produce lung tumors in animal studies. EPA has classified nickel carbonyl as a Group B2, a probable human carcinogen a Milligrams per kilogram per day is one way to measure the amount of the contaminant that is consumed in food. Exceedance of the RfD does not imply that an adverse health effect would necessarily occur. As the amount and frequency of exposures exceeding the RfD increase, the probability of adverse health effects also increases.
Nickel carbonyl is the most acutely toxic nickel compound.
The soluble compounds, such as nickel acetate, were the most toxic, and the insoluble forms, such as nickel powder, were the least toxic. Contact dermatitis is the most common effect in humans from nickel exposure. Cases of nickel contact dermatitis have been reported following occupational and non-occupational exposure, with symptoms of itching of the fingers, wrists, and forearms. These include direct respiratory effects such as asthma due to primary irritation or an allergic response, and an increased risk of chronic respiratory tract infections. Animal studies have reported effect on the lungs, kidneys, and immune system from inhalation exposure to nickel.