Cobalt (chemical symbol Co) is a metal that may be stable (nonradioactive,
as found in nature), or unstable (radioactive, man-made). The
most common radioactive isotope of cobalt is cobalt-60.
Who discovered cobalt and cobalt-60?
In 1735, a Swedish scientist, George Brandt, demonstrated that
a blue color common in colored glass was caused by a new element,
cobalt. Previously, people thought that bismuth, which occurs
in nature with cobalt, was the cause. Radioactive cobalt-60 was
discovered by Glenn T. Seaborg and John Livingood at the University
of California - Berkeley in the late 1930's.
Where do cobalt and cobalt-60 come from?
Nonradioactive cobalt occurs naturally in various minerals, and
has been used for thousands of years to impart blue color to ceramic
and glass. The radionuclide, cobalt-60, is produced for commercial
use in linear accelerators. It is also produced as a by-product
of nuclear reactor operations, when structural materials, such
as steel, are exposed to neutron radiation.
What are the properties of cobalt-60?
Cobalt (including cobalt-60) is a hard, brittle, gray metal with
a bluish tint. It is solid under normal conditions and is generally
similar to iron and nickel in its properties. In particular, cobalt
has can be magnetized similar to iron.
What is cobalt-60 used for?
Cobalt-60 is used in many common industrial applications, such
as in leveling devices and thickness gauges, and in radiotherapy
in hospitals. Large sources of cobalt-60 are increasingly used
for sterilization of spices and certain foods. The powerful gamma
rays kill bacteria and other pathogens, without damaging the product.
After the radiation ceases, the product is not left radioactive.
This process is sometimes called "cold pasteurization."
Cobalt-60 is also used for industrial radiography, a process
similar to an x-ray, to detect structural flaws in metal parts.
Radionuclides, such as cobalt-60, that are used in industry or
medical treatment are encased in shielded metal containers or
housings, and are referred to as radiation ‘sources.' The
shielding keeps operators from being exposed to the strong radiation.
Occasionally, medical or industrial radiation sources are lost
or stolen. We call these "orphan sources." They pose
a significant risk:
On a number of occasions, people have handled them, not knowing
what they were, and have been exposed.
Sometimes sources find their way into municipal landfills,
where it is illegal to dispose of them.
Because of their metallic housings, sources can get mixed
in with scrap metal and pass undetected into scrap metal recycling
facilities. If melted in a mill, they can contaminate the entire
batch of metal and the larger facility, costing millions of
dollars in lost productivity and cleanup costs. The scrap industry
uses radiation detectors to screen incoming material. However,
sources that are under large loads may be undetected initially.
Cobalt-60 can also be released to the environment through leaks
or spills at nuclear power plants, and in solid waste originating
from nuclear power plants. Nuclear Regulatory Commission regulations
allow small amounts of cobalt-60 to be released into the air,
or poured down drains as part of a liquid.
How does cobalt-60 change in the environment?
Cobalt-60 undergoes radioactive decay with the emission of beta
particles and strong gamma radiation. It ultimately decays to
nonradioactive nickel. The half-life of cobalt-60 is 5.27 years.
This is short enough to make isolation a useful treatment strategy
for contaminated areas. In some cases, simply waiting 10 to 20
years allows for sufficient decay to make the site acceptable
for use again.
How do people come in contact with cobalt-60?
Most exposure to cobalt-60 takes place intentionally during medical
tests and treatments. Such exposures are carefully controlled
to avoid the adverse health impacts and to maximize the benefits
of medical care. Accidental exposures may occur as the result
of loss or improper disposal of medical and industrial radiation
sources. Though relatively rare, exposure has also occurred by
accidental mishandling of a source at a metal recycling facility
or steel mill.
How does cobalt-60 get into the body?
People may ingest cobalt-60 with food and water that has been
contaminated, or may inhale it in contaminated dust. The major
concern posed by cobalt-60, however, is external exposure to its
strong gamma rays. This may occur if you are exposed to an orphaned
source, or if you come in contact with waste from a nuclear reactor
(though this is very unlikely).
What does cobalt do once it gets into the body?
Once in the body, some cobalt-60 is quickly eliminated in the
feces. The rest is absorbed into the blood and tissues, mainly
the liver, kidney, and bones. Absorbed cobalt leaves the body
slowly, mainly in the urine.
All ionizing radiation, including that of cobalt-60, is known
to cause cancer. Therefore, exposures to gamma radiation from
cobalt-60 result in an increased risk of cancer.
External expsosure to cobalt-60 is usually considered a greater
threat, because it emits such strong gamma rays. The magnitude
of the health risk depends on the quantity of cobalt-60 involved
and on exposure conditions:
length of exposure
distance from the source (for external exposure)
whether the cobalt-60 was ingested or inhaled.
Is there a medical test to determine exposure to cobalt-60?
Yes, there are several. However they are not routinely available
in a doctor's office because they require special laboratory equipment.
Some tests can measure the amount of cobalt-60 in urine, even
at very low levels. Scientist can estimate the amount in the body
from the amount measured in the urine.
A technique called "whole-body counting" can detect
gamma radiation emitted by cobalt-60 in the body. A variety of
portable instruments can directly measure cobalt-60 on the skin
or hair.
Other techniques include measuring the level of cobalt-60 in
soft tissues (such as organs) and in blood, bones, milk, or feces
You need special equipment to detect the presence of any radionuclide.
What can I do to protect myself and my family from cobalt-60?
You are unlikely to encounter cobalt-60 unless you undergo certain
medical treatments. Thorough discussions with your doctor about
the amount of exposure and potential alternatives allow you to
make informed decisions about the relative risks.
Although it is very unlikely, you may accidentally encounter
a sealed radiation source containing cobalt-60 that has escaped
proper control ("orphaned sources").
Cobalt-60 is regulated by both the EPA and the Nuclear Regulatory
Commission. The Nuclear Regulatory Commission has jurisdiction
over the licensing and use of cobalt-60 sources, and disposal
of cobalt-60 sources.
EPA has several regulations that control cobalt-60 in the environment,
including standards for the maximum amount of cobalt-60 that nuclear
facilities may release to the air, maximum contaminant levels
for cobalt-60 in drinking water, and risk-based
criteria for soil and groundwater at sites previously contaminated
with cobalt-60.
