Hair appears
to be an accurate medium for evaluation of total tissue burden
of nickel. Most exposure leading to elevated hair levels is
via dust from nearby industries including electrometallurgical
emissions. Nickel accumulates with age and smoking, perhaps
explaining why tissue levels are highest in patients who died
of cardiovascular disease.
Given
nickel's ability to cause contact dermatitis, and its observed
perturbation of immunoglobulin levels, elevated hair levels
may serve as an indicator of possible immune dysfunction,
as well as a potentially useful marker of cardiovascular problems.
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 volcanoes.
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.
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.
