Naturally Occurring Contamination

Naturally Occurring Contamination

Naturally occurring contamination comes from substances already in the environment, rather than from chemicals or other hazardous materials used or manufactured by humans. Radon is one of those naturally occurring contaminants. Radon seeps into homes from the rock under the building’s foundation.

Human activities sometimes create conditions allowing exposure to a naturally occurring contaminant. For example, a mining operation might disturb naturally occurring contaminants in soil and rock. Rainwater might then wash contaminants such as lead out of exposed piles of soil and rock. The lead was naturally occurring but only became a problem when human activity disturbed it. Table 4.1 lists more examples of naturally occurring contamination.

Table 4.1 Naturally occurring contamination
Naturally occurring contaminant Places contaminant is sometimes found Reason for concern
Arsenic In water. Some parts of the United States have high naturally occurring levels of inorganic arsenic. Inorganic arsenic in large doses can cause a sore throat or irritated lungs. Swallowing very high levels of arsenic can result in death. Exposure to lower levels can cause nausea and vomiting, decreased production of red and white blood cells, abnormal heart rhythm, damage to blood vessels, and a sensation of “pins and needles” in hands and feet. Swallowing or breathing low levels of inorganic arsenic for a long time can cause a darkening of the skin and the appearance of small “corns” or “warts” on the palms, soles, and torso. Skin contact with inorganic arsenic can cause redness and swelling.
Asbestos In soil. Natural weathering and human activities can disturb naturally occurring asbestos-bearing rock or soil and release mineral fibers into the air. Asbestos mainly affects the lungs and the membrane that surrounds the lungs. Breathing high levels of asbestos fibers for a long time may result in scar-like tissue in the lungs and in the pleural membrane (lining) that surrounds the lung. This disease is called asbestosis and is usually found in workers exposed to asbestos, but not in the general public. People with asbestosis have difficulty breathing, often have a cough, and in severe cases, heart enlargement. Asbestosis is a serious disease and can eventually lead to disability and death.
Fluoride7 In water. High levels of fluoride occur naturally in some areas. Fluoride in small amounts helps prevent tooth cavities. In adults, exposure to high levels of fluoride can result in denser bones. However, if exposure is high enough, these bones might be more fragile and brittle, and there could be a greater risk of the bone breaking.
Lead In water. Most lead in water comes from the pipes or materials that help supply the water. Lead can sometimes be found naturally in groundwater. Lead can affect almost every organ and system in the body. The main target for lead toxicity is the nervous system, both in adults and children. Long-term exposure of adults can result in decreased performance in some tests that measure functions of the nervous system. It can also cause weakness in fingers, wrists, or ankles. Lead exposure also causes small increases in blood pressure, particularly in middle-aged and older people and can cause anemia. Exposure to high lead levels can severely damage the brain and kidneys in adults or children and ultimately cause death. In pregnant women, high-levels of exposure to lead can cause miscarriage. High-level exposure in men can damage the organs responsible for sperm production
Manganese In water. Manganese is a mineral that is found naturally in rocks and soil. It can get into drinking water. It can also give water an odd taste, smell or color. Manganese is an essential nutrient, and eating a small amount of it each day is important to stay healthy. The most common health problems in workers exposed to high levels of manganese involve the nervous system. These health effects include behavioral changes and other nervous system effects, such as slowed and clumsy movement. This combination of symptoms, when severe, is referred to as manganism. Other less severe nervous system effects, such as slowed hand movements, have affected some workers exposed to lower concentrations in the workplace. Studies in children have suggested that extremely high levels of manganese exposure can harm brain development, resulting in behavior changes and decreased ability to learn and remember.
Nitrates and nitrites In water. Nitrates and nitrites come from the breakdown of nitrogen compounds in the soil. Flowing groundwater picks them up from the soil. Nitrates and nitrites in large amounts are particularly threatening to infants (for example, when mixed in formula). Some people who ate food or drank fluids that contained unusually high levels of nitrite experienced methemoglobinemia (decreased ability of the blood to carry oxygen to tissues) and related symptoms, such as decreases in blood pressure, increased heart rate, headaches, abdominal cramps, and vomiting and some people died.
Radon In air. Radon is a gas that is a natural product of the breakdown of uranium in the soil. Radon is most dangerous when inhaled. Radon undergoes radioactive decay and can emit high-energy alpha particles, which are the main source of health concerns. The main isotope of health concern is radon-222 (222Rn). Many scientists believe that the alpha radiation dose from long-term exposure to high levels of radon emissions in the air increases the chance of getting lung cancer.
In water. Using household water containing radon contributes to elevated indoor radon levels. Radon is less dangerous when consumed in water, but remains a risk to health.
Radionuclides In water. Radionuclides are radioactive elements, such as uranium and radium that might be in groundwater. Radionuclides can increase the risk for cancer. Swallowing water-soluble uranium compounds affects the kidneys at lower doses than does exposure to insoluble uranium compounds. Exposure to radium can affect the blood (anemia) and eyes (cataracts). It also can affect the teeth, causing an increase in broken teeth and cavities. Exposure to high levels of radium results in an increased incidence of bone, liver, and breast cancer
Selenium In water. Occasionally, drinking water contains high levels of selenium, usually in areas where high levels of selenium in soil contribute to the content of the water. Selenium exposure at high levels can cause adverse health effects. Short-term oral exposure to high concentrations of selenium can cause nausea, vomiting, and diarrhea. Chronic oral exposure to high concentrations of selenium compounds can produce a disease called selenosis. The major signs of selenosis are hair loss, nail brittleness, and neurological abnormalities (such as numbness and other odd sensations in the hands and feet).
Uranium In water. Uranium is naturally present in bedrock in many locations throughout the United States. When a drinking water well is drilled through bedrock containing uranium, the uranium can get into the drinking water. Natural uranium and depleted uranium have the identical chemical effect on your body. Kidney damage has occurred in humans and animals after inhaling or swallowing uranium compounds. However, kidney damage has not been consistently found in soldiers who have had uranium metal fragments in their bodies for several years. Swallowing water-soluble uranium compounds will affect the kidneys at lower doses than will exposure to insoluble uranium compounds. Health effects of natural and depleted uranium result from chemical effects and not radiation

7 ATSDR’s concern for fluoride exposures is not related to recommendations for fluoride use in toothpaste or water supplies to prevent tooth decay. Information on CDC’s recommendations for fluoride and dental health are available at:

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Page last reviewed: October 30, 2018