ATSDR TOXZINE

URANIUM

1 . . . . . . . . . . . . . . . . . . . . . . . Uranium Overview

2 . . . . . . . . . . . Uranium and the Environment

4 . . . . . . . . . . . . . . . . . . . . Exposure to Uranium

5 . . . . . . . . . . . . . . . . . . . Uranium and the Body

7 . . . . . . . . . . . . . . . Health Effects of Exposure

9 . . . . . . . . . . . . . . . . . . . Uranium and Children

10 . . . . . . . . . . . . . . . Reducing Risk of Exposure

11 . . . . . . . . . . . . . . . . . . . . . . . . . Exposure Testing

12 . . . . . . . . Governmental Recommendations

13 . . . . . . . . . . . . . . . . . . . Additional Information

CONTENTS

1

URANIUM 

OVERVIEW

Uranium is a naturally occurring radioactive element. 

It is found in very small amounts in nature in the form of minerals, but may be 

processed into a silver-colored metal. Rocks, soil, surface and groundwater, air, and 

plants and animals all contain varying amounts of uranium. If the amount is great 

enough, the uranium may be present in commercial concentrations, called ore, and 

can be mined. Uranium is almost as hard as steel and much denser than 

lead. Natural uranium is used to make enriched uranium; depleted uranium 

is the leftover product. Enriched uranium is used to make fuel for nuclear 

power plants. Depleted uranium is used as a counterbalance on helicopter 

rotors and airplane control surfaces, as a shield to protect against ionizing 

radiation, as a component to munitions to help them penetrate enemy 

armored vehicles, and as armor in some parts of military vehicles.

Natural uranium is a mixture of three isotopes: 234U, 235U, and 238U.

The most common isotope is 238U; it makes up about 99% of natural 

uranium by mass. All three isotopes behave the same chemically, but they 

have different radioactive properties. The half-lives of uranium isotopes (the 

amount of time needed for half of the isotope to give off its radiation and 

change into a different element) are very long. The least radioactive isotope 

is 238U with a half-life of 4.5 billion years. Depleted uranium is a mixture of 

the same three uranium isotopes, except that it has very little 234U and 235U.

It is less radioactive than natural uranium. Enriched uranium is another mixture of 

isotopes that has more 234U and 235U than natural uranium. Enriched uranium is more 

radioactive than natural uranium.

Natural uranium is radioactive but poses little radioactive danger because it gives 

off very small amounts of radiation. Uranium transforms into another element 

and gives off radiation. In this way uranium transforms into thorium and gives off 

a particle called an alpha particle or alpha radiation. Uranium is called the parent, 

and thorium is called the transformation product. When the transformation product 

is radioactive, it keeps transforming until a stable product is formed. During these 

decay processes, the parent uranium, its decay products, and their subsequent 

decay products each release radiation. Radon and radium are two of these products.

Unlike other kinds of radiation, the alpha radiation ordinarily given off by uranium 

cannot pass through solid objects, such as paper or human skin. ◆

Natural uranium 

is radioactive 

but poses little 

radioactive danger 

because it gives 

off very small 

amounts 

of radiation.
2

URANIUM AND 

THE ENVIRONMENT 

Uranium is a naturally occurring radioactive material 

that is present to some degree in almost everything in our 

environment, including soil, rocks, water, and air.

It oxidizes readily, so it is found in minerals but not as free uranium in the 

environment. Uranium can be redistributed in the environment through wind 

and water erosion, and released into the environment through volcanic eruptions.

Inactive mines and mills may continue to release uranium into the environment.

Inactive uranium industries may continue to release uranium into the environment.

In the air, uranium exists as dust. The very small particles of uranium found in dust 

can fall onto water, plants, and land. Rain increases the rate at which uranium in air 

settles to the ground.
3

Uranium in water comes from different sources. Uranium can be found in drinking 

water, typically at low levels. Higher levels in drinking water can be found in wells 

drilled in uranium-rich rock formations. Uranium in surface water can be transported 

large distances. Some of the uranium in water will stick to sediment and other 

particles in the water.

Uranium is naturally present in nearly all rocks and soils. Uranium deposited on land 

can mix into soil, wash into surface water, or stick to plant roots.

Uranium can stick to plant roots. Unwashed potatoes, radishes, and other root 

vegetables are a primary source of uranium in the diet. Human daily intake has been 

estimated to range from 0.9 to 1.5 micrograms of uranium per day (μg/day). ◆

Uranium can be 

found in 

drinking water, 

typically at 

low levels.
4

EXPOSURE 

TO URANIUM

Since uranium is found everywhere in small amounts, 

you always take it into your body from the air, water, food, 

and soil.

For most people, food and drinking water are the main sources of uranium exposure.

Root crops such as potatoes, parsnips, turnips, and sweet potatoes contribute the 

highest amounts of uranium to the diet. The amount of uranium in these foods is 

directly related to the amount of uranium in the soil in which they are grown.

People who work with materials and products that contain uranium may be exposed 

at work. This includes workers who mine, mill, or process uranium or make items that 

contain uranium. People who work with phosphate fertilizers may also be exposed to 

higher levels of uranium because the phosphate rock used in the production of the 

fertilizer may contain significant quantities of uranium.

People who live near uranium mining, processing, and manufacturing facilities 

could be exposed to more uranium than the general population. People may also be 

exposed if they live near areas where depleted uranium weapons are used.

In most areas of the United States, low levels of uranium are found in the drinking 

water. Higher levels may be found in areas with elevated levels of naturally occurring 

uranium in rocks and soil. ◆

People who live near 

uranium mining, 

processing, and 

manufacturing facilities 

could be exposed to more 

uranium than 

the general population.
5

URANIUM AND 

THE BODY 

We take uranium into our bodies in the food we eat, water we 

drink, and air we breathe. Uranium can also enter your body 

through dermal contact. 

When you breathe uranium dust, some of it is exhaled. The remainder gets retained; 

some comes up to be swallowed, some enters the bloodstream, and the rest stays 

there and can build up slowly over a lifetime. This occurs with other substances 

as well. Only about 0.76–5% of the uranium a person breathes will get into the 

bloodstream through the respiratory tract (nose, mouth, throat, lungs). Some 

uranium compounds are slowly cleared from the lungs.

When you eat foods and drink liquids containing uranium, most of it leaves your 

body within a few days and never enters your blood. Only about 0.1–6% of the

uranium a person ingests will get into the bloodstream through the gastrointestinal 

tract (mouth, stomach, intestines). Uranium compounds that dissolve in water enter 

the bloodstream more easily than uranium compounds poorly soluble in water.

A very small amount of uranium can be absorbed through the skin; water-soluble 

uranium compounds are the most easily absorbed.

Most of the inhaled and ingested uranium is not absorbed and leaves the body in 

the feces. Absorbed uranium leaves your body in the urine. Some inhaled uranium 

can stay in the lungs for a long time.

Most of the 

inhaled and ingested 

uranium is not 

absorbed.
6

Uranium that is absorbed is deposited throughout the body; the highest levels are 

found in the bones, liver, and kidneys. Sixty-six percent of the uranium in the body 

is found in your bones. It can remain in the bones for a long time; the half-life of 

uranium in bones is 70–200 days (this is the amount of time that it takes for half of 

the uranium to leave the bones). Most of the uranium that is not in bones leaves the 

body in 1–2 weeks. ◆

Uranium that is 

absorbed is deposited 

throughout the body.
7

HEALTH EFFECTS

OF EXPOSURE 

Natural and depleted uranium have the identical chemical 

effect on your body. The health effects of natural and depleted 

uranium are due to chemical effects and not to radiation.

Uranium’s main target is the kidneys. Kidney damage has been seen in humans and 

animals after inhaling or ingesting uranium compounds. Ingesting water-soluble 

uranium compounds will result in kidney effects at lower doses than following 

exposure to insoluble uranium compounds. Inhaled insoluble uranium compounds 

can also damage the respiratory tract.

No health effects, other than kidney damage, have been consistently found in 

humans after inhaling or ingesting uranium compounds or in soldiers with uranium 

metal fragments in their bodies. Rats ingesting uranium over a long time had 

neurobehavioral changes and changes in the levels of certain chemicals in the brain.

Uranium has been shown to decrease fertility in some studies of rats and mice; other 

studies have not found this effect. Very soluble uranium compounds on the skin 

caused skin irritation and mild skin damage in animals.

Neither the National Toxicology Program (NTP), International Agency for Research on 

Cancer (IARC), nor the EPA have classified natural uranium or depleted uranium with 

respect to carcinogenicity. ◆

Uranium’s 

main target 

is the kidneys.
8

URANIUM 

AND CHILDREN 

Like adults, children are exposed to small amounts of uranium 

in air, food, and drinking water. 

No data describe the effects of exposure to uranium on children. Although we think 

that children would likely show the same health effects as adults, we do not know 

whether children are more susceptible than adults to uranium effects.

We do not know whether uranium can harm an unborn child. No scientifically 

strong human study that has shown birth defects due to uranium exposure has 

been identified. Some studies in animals exposed to high levels of uranium during 

pregnancy, which caused toxicity in the mothers, have resulted in early deaths and 

birth defects in the young. It is not clear if this can happen in the absence of effects 

on the mother. Other studies have not found birth defects. In some rat studies, 

enriched uranium exposure during pregnancy caused changes in brain function in 

the offspring. Similar studies found changes in the ovaries of the female offspring.

One study reported that giving a high amount of uranium to newborn rats altered the 

tooth formation. ◆
9

REDUCING RISK 

OF EXPOSURE 

If your doctor finds that you have been exposed to significant 

amounts of uranium, ask whether your children might also 

be exposed. Your doctor might need to ask your state health 

department to investigate.

To help reduce your exposure to uranium, avoid eating root vegetables grown in soils 

with high levels of uranium. Consider washing fruits and vegetables grown in that 

soil and discard the outside portion of root vegetables. Consider having your water 

tested if you suspect that your drinking water might have elevated levels of uranium.

If elevated levels are found, consider using bottled water. If you live near a hazardous 

waste site with high amounts of uranium that are not controlled, do not let your 

children play outside in the dirt. Children put dirt in their mouths, and uranium is in 

this dirt. Also, make sure your children wash their hands often, especially 

before eating. ◆

If you live near 

a hazardous waste 

site with high 

amounts of uranium 

that are not controlled, 

do not let your children 

play outside in the dirt.
10

EXPOSURE 

TESTING 

Natural uranium is in your normal diet, so there will always 

be some level of uranium in all parts of your body.

If in addition you are exposed to depleted uranium, it adds to the total uranium level 

in your body. There are reliable medical tests that can detect whether uranium is in 

your body.

Uranium can be measured in blood, urine, hair, and body tissues. Normally, urinary 

sampling is the preferred method for assessing uranium exposure. The amount of 

radiation from uranium in your body can also be measured.

Most tests are for total uranium; however, expensive tests are available to estimate 

the amounts of both natural and depleted uranium that are present.

Most uranium leaves the body within a few days. High amounts in your urine might 

show that you have been exposed to high amounts of uranium within the last week 

or so. ◆
11

GOVERNMENTAL 

RECOMMENDATIONS 

Recommendations and regulations are updated periodically 

as more information becomes available. 

For the most current information, check with the federal agency or organization that 

issued the regulation or recommendation.

Some regulations and recommendations for uranium are in the chart below.

FEDERAL 

ORGANIZATION

REGULATION OR 

RECOMMENDATION

U.S. Environmental 

Protection Agency (EPA) 

The U.S. EPA has established a maximum contaminant 

level of 0.03 mg/L and set a maximum contaminant 

level goal of no uranium in drinking water.

Occupational Safety and 

Health Administration 

(OSHA)

OSHA set a legal limit for worker exposure to uranium 

in workplace air of 0.05 mg uranium/m3

 for soluble 

uranium and 0.25 mg uranium/m3 for insoluble 

uranium averaged over an 8-hour work day.

National Institute of 

Occupational Safety and 

Health (NIOSH)

NIOSH recommends that worker exposure to uranium 

in workplace air not exceed an exposure limit of 

0.05 mg uranium/m3

 for soluble uranium and 0.2 mg 

uranium/m3

 for insoluble uranium averaged for up 

to a 10-hour work day. NIOSH also recommends that 

exposure to soluble uranium not exceed 0.6 mg U/m3

for more than 15 minutes.

U.S. Nuclear Regulatory 

Commission (USNRC)

The USNRC has established derived air concentrations 

of 0.0005, 0.0003, and 0.00002 microcuries/m3

, averaged 

for a working year of 2,000 hours for workers exposed 

to a form of uranium that is excreted at fast, medium, 

and slow rates, respectively.
12

ADDITIONAL 

INFORMATION 

If you have any more questions or concerns, please contact 

your community or state health or environmental quality 

department or contact ATSDR at the address and phone 

number below. 

Agency for Toxic Substances and Disease Registry

Division of Toxicology and Human Health Sciences

1600 Clifton Road NE, Mailstop F-57

Atlanta, GA 30329-4027

Toll-free information and technical assistance:

1-800-CDCINFO (1-800-232-4636)

For additional information, check out ATSDR’s Toxic Substances Portal 

for Uranium. 

http://www.atsdr.cdc.gov/substances/toxsubstance.asp?toxid=77
13
something like: A publication from the Centers for 

Disease Control and Prevention

ATSDR TOXZINE A publication of CDC/ATSDR

CS251228-A