Urinary excretion of nickel bound to cysteine or other thiol compounds (such as glutathione) or to amino acids (histidine, aspartic acid, arginine) is the predominant mode of excretion. With the exception of specific occupational exposures, most absorbed Ni comes from food or drink, and intakes can vary by factors exceeding 100 depending upon geographical location, diet, and water supply. Nickel is present in a surprisingly large number of foods and food products, including: hydrogenated oils, black tea, nuts and seeds, soy milk and chocolate milk, chocolate and cocoa powders, certaincanned and processed foods, including meat and fish, certain grains, including: oats, buckwheat, whole wheat and wheat germ. 1 to 10% of dieatry Ni may be absorbed from the gastrointestinal tract into the blood. Urine reflects recent exposure to nickel and ay vary widely in nickel content from day to day.

Other sources of Ni include cigarettes (2 to 6 mcg Ni per average cigarett), diesel exhaust, Ni-Cd batteries, nonprecious, seminprecious dental materials, electroplating, plated objects, costume jewelry and pigments (usually for ceramics or glass), Arc welding, and metallurgical processes.

Most clinically relavant Ni exposures are manifested as dermatoses - contact dermatitis and atopic dermatitis. However, Ni hypersensitizes the immune system and may cause hyperallergenic responses to many different substances. Because Ni can displace zinc from binding sites on enzymes it can affect abnormal enzymatic activity. Nickel sensitivity is observed to be three to five times more prevelant in females than in males.

Other laboratory tests or possible clinical findings that may be associated with Ni exposure are; hair elements analysis, presentation of multiple allergic sensitivities, dermatitis, positive patch test for "Ni allergy", proteinuria, hyperaminoaciduria (by 24-hour urine amino acid analysis). Administration of EDTA or sulfhydryl agents (DMPS, DMSA, D-penicillamine) may increase urine Ni levels; such chelator- induced elevations may or may not be associated with adverse health effects.