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Nickel

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Introduction

Pure nickel is a hard, silvery white metal, which has properties that make it very desirable for combining with other metals to form mixtures called alloys. Some of the metals that nickel can be alloyed with are iron, copper, chromium, and zinc. These alloys have important uses such as in the making of metal coins and jewelry and in industry for making items such as valves and heat exchangers. Most nickel is used to make stainless steel. Compounds of nickel combined with many other elements, including chlorine, sulfur, and oxygen, exist. Many of these compounds dissolve fairly easily in water and have a characteristic green color. Nickel and its compounds have no characteristic odor or taste. Nickel compounds are used for nickel plating, to color ceramics, to make some batteries, and as substances known as catalysts to increase the rate of chemical reactions.

Nickel combined with other elements occurs naturally in the earth's crust, is found in all soils, and is also emitted from volcanos. Nickel is the 24th most abundant element, and in the environment it is found primarily as oxides or sulfides. Nickel is also found in meteorites and in lumps of minerals on the floor of the ocean, known as sea floor nodules. The earth's core is believed to contain large amounts of nickel. Nickel is released into the atmosphere during nickel mining and by industries that convert scrap or new nickel into alloys or nickel compounds or by industries that use nickel and its compounds. These industries may also discharge nickel in waste water. Nickel is also released into the atmosphere by oil-burning power plants, coal-burning power plants, and trash incinerators.

There is only one nickel mine in operation in the United States. The mine is located in Riddle, Oregon. Most of our new nickel is imported from Canada. Much of our domestic nickel comes from recycling nickel-containing alloys.

Fate & Transport

Nickel may be released to the environment from the stacks of large furnaces used to make alloys or from power plants and trash incinerators. The nickel that comes out of the stacks of the power plants is attached to small particles of dust that settle to the ground or are taken out of the air in rain. It will usually take many days for nickel to be removed from the air. If the nickel is attached to very small particles, removal can take longer than a month. Nickel can also be released in waste water. Most nickel will end up in the soil or sediment where it is strongly attached to particles containing iron or manganese. Under acidic conditions, nickel is more mobile in soil and may seep into groundwater. Nickel does not appear to concentrate in fish. Two recent studies indicate that it does not accumulate in plants growing on land that has been treated with nickel-containing sludge or in small animals living on that land.

Exposure Pathways

You may be exposed to nickel by breathing air, drinking water, eating food, and smoking tobacco and by skin contact with soil, water, and metals containing nickel as well as with metals plated with nickel. Stainless steel and coins contain nickel. Jewelry is often plated with nickel or made from nickel alloys. Patients may be exposed to nickel in artificial body parts made from nickel-containing alloys.

We do not always know to what form of nickel we are exposed. Much of the nickel found in sediment, soil, and rock is so strongly attached to dust and soil particles or embedded in minerals that it is not readily taken up by plants and animals and cannot easily affect your health. We do not know what forms of nickel are found at most hazardous waste sites.

Nickel in air is attached to small particles. In 1982, the average concentration of nickel in air in 111 U.S. cities ranged from 1 to 86 ng/m3 (1 ng/m3 is equivalent to 1 billionth of a gram in a cubic meter of air).

The concentration of nickel in water from rivers and lakes is very low. The average concentration of nickel is generally less than 10 parts in a billion parts (ppb) in rivers and lakes. The level of nickel in water is often so low that we cannot measure it unless we use very sensitive instruments. The average concentration of nickel in drinking water is about 2 ppb. However, you may be exposed to higher than average levels of nickel in drinking water if you live near industries that process or use nickel.

Soil generally contains between 4 and 80 parts of nickel in a million parts of soil (ppm; 1 ppm is 1,000 times greater than 1 ppb). The highest soil concentrations (up to 9,000 ppm) are found near industries where nickel is extracted from ore. High concentrations of nickel occur because dust released from stacks during processing settles out of the air. You may be exposed to nickel in soil by skin contact. Children may also be exposed to nickel by eating soil.

Food contains nickel and is the major source of nickel exposure for the general population. You eat about 170 micrograms (ug; 1 ug = 1,000 ng) of nickel in your food every day. Foods naturally high in nickel include chocolate, soy beans, nuts, and oatmeal. Our daily intake of nickel from drinking water is only about 2 ug. We breathe in between 0.1 and 1 ug nickel/day, excluding nickel in tobacco smoke. We are exposed to nickel when we handle coins and touch other metals containing nickel.

You may be exposed to higher than background levels of nickel if you work in industries that process or use nickel. You may be exposed to nickel by breathing dust or furmes (as from welding) or by skin contact with nickel-containing metal and dust or solutions containing dissolved nickel compounds. A national survey conducted from 1980 to 1983 estimated that 727,240 workers are potentially exposed to nickel metal, nickel alloys, or nickel compounds.

Metabolism

Nickel can enter your body when you breathe in air containing nickel, when you drink water or eat food that contains nickel, and when your skin is in contact with nickel. If you breathe in air that contains nickel dust, the amount of inhaled nickel that reaches your lungs and enters your blood depends on the size of the dust particles. If the particles are large, they stay in your nose; if the particles are small they can enter deep into your lungs. More nickel is absorbed from your lungs into your body when the dust particles are able to dissolve easily in water. When the particles do not dissolve easily in water, the nickel will tend to remain in your lungs for a long time. Some of these nickel particles can leave the lungs with mucus that you spit out or swallow. More nickel will pass into your body through your stomach and intestines if you drink water containing nickel than if you eat food containing the same amount of nickel. A small amount of nickel can enter your bloodstream after being placed on your skin. After nickel gets into your body, it can go to all organs, but it mainly goes to the kidneys. The nickel that gets into your bloodstream leaves in the urine. After nickel is eaten, almost all of it leaves quickly in the feces, and the small amount that gets into your body leaves in the urine.

Health Effects

Nickel is essential to maintain health in animals. Although a lack of nickel has not been found to effect the health of humans, a small amount of nickel is probably also essential for humans.

Much of our knowledge of nickel toxicity is based on animal studies. Rats and mice may die after eating large amounts of nickel. Eating levels of nickel very much greater than the levels normally found in food causes lung disease in dogs and rats and affects the stomach, blood, liver, kidneys, and immune system in rats and mice. Effects on reproduction and birth defects also were found in rats and mice eating or drinking very high levels of nickel. The studies in animals were completed using high levels of soluble nickel which is more readily absorbed by the gastrointestinal tract than the nickel compounds usually found in water and food.

The most common adverse health effect of nickel in humans is an allergic reaction to nickel. People can become sensitive to nickel when jewelry or other things containing nickel are in direct contact with the skin. Wearing earrings containing nickel in pierced ears may also sensitize people to nickel. Once a person is sensitized to nickel, further contact with the metal will produce a reaction. The most common reaction is a skin rash at the site of contact. In some sensitized people dermatitis may develop at a site away from the site of contact. For example, hand eczema is fairly common among people sensitized to nickel. Less frequently, some people who are sensitive to nickel have asthma attacks following exposure to nickel. People who are sensitive to nickel have reactions when nickel is in contact with the skin, and some sensitized individuals react when they eat nickel in food or water, or breath dust containing nickel. More women are sensitive to nickel than men. This difference between men and women is thought to be a result of greater exposure of women to nickel through jewelry and other metal items.

People who are not sensitive to nickel must eat very large amounts of nickel to suffer adverse health effects. Workers who accidently drank light green water containing 250 ppm nickel from a contaminated drinking fountain had stomachaches and suffered adverse effects to the blood (increased red blood cells) and kidneys (increased protein in the urine). A child who ate 5,700 milligrams (mg) (1 milligram = 1 thousandth of a gram) of nickel as crystals of nickel sulfate died from heart failure.

The most serious effects of nickel, such as cancer of the lung and nasal sinus, have occurred in people who have breathed nickel dust while working in nickel refineries or in nickel processing plants. The levels of nickel in the workplace were much higher than background levels. Lung and nasal sinus cancers occurred when the workers were exposed to more than 1 mg of nickel per cubic meter of air as nickel compounds that dissolved easily in water (such as nickel sulfate and nickel chloride) or 10 mg nickel/m3 as nickel compounds that were hard to dissolve (such as nickel subsulfide). The Department of Health and Human Services has determined that nickel and certain nickel compounds may be reasonably anticipated to be carcinogens. The International Agency for Research on Cancer (IARC) has determined that some nickel compounds are carcinogenic to humans and that metallic nickel may possibly be carcinogenic to humans. The EPA has determined that nickel refinery dust and nickel subsulfide are human carcinogens. Other lung effects including chronic bronchitis and reduced lung function have been observed in workers breathing nickel.

Information excerpted from:

Toxicological Profile for Nickel August 1995 Draft Update

Agency for Toxic Substances and Disease Registry
U.S. Dept. of Health and Human Services