Arsenic, a naturally occurring element, can combine with either inorganic or organic substances to form many different compounds. Inorganic arsenic compounds are in soils, sediments, and groundwater. These compounds occur either naturally, or as a result of mining, ore smelting, or when using arsenic for industrial purposes. Organic arsenic compounds exist mainly in fish and shellfish.
In the past people used inorganic forms of arsenic in pesticides and paint pigment. People also used them as wood preservatives and as a treatment for a variety of ailments. Today laws restrict using arsenic-containing pesticides, wood preservatives, and medicines.
How People Are Exposed to Arsenic
People are most likely exposed to inorganic arsenic through drinking water. This is especially true in areas with water sources that naturally have higher levels of inorganic arsenic. People can also be exposed to inorganic arsenic by eating such foods as rice and some fruit juices. Other sources of inorganic arsenic exposure include contact with contaminated soil or dust, or with wood preserved with arsenic compounds.
Exposure to organic arsenic compounds happens when people eat seafood. These forms of arsenic are considered to be non-toxic or considerably less toxic than inorganic arsenic.
How Arsenic Affects People’s Health
Unusually large doses of inorganic arsenic can cause symptoms ranging from nausea, vomiting, and diarrhea to dehydration and shock. Long-term exposure to high levels of inorganic arsenic in drinking water is associated with certain medical conditions. These conditions include skin disorders, an increased risk for diabetes, high blood pressure, and several types of cancer. Inorganic arsenic and arsenic compounds are considered to be cancer-causing chemicals.
Studies have not found organic arsenic in seafood to be toxic to humans.
Levels of Arsenic in the U.S. Population
In the Fourth National Report on Human Exposure to Environmental Chemicals (Fourth Report), CDC scientists measured total arsenic, and seven different forms (or species) of arsenic. They measured these substances in the urine of 2,557 participants, aged six years and older, who took part in the National Health and Nutrition Examination Survey (NHANES) in 2003–2004. By measuring arsenic in urine, scientists can estimate the amount of arsenic that has entered people’s bodies within the past two or three days.
- The body converts inorganic arsenic into the breakdown product (metabolite) called dimethylarsinic acid (DMA). DMA is also found in such foods as fish, poultry, fruits and grains. NHANES results found DMA and arsenobetaine to be the major components of urinary total arsenic levels. Arsenobetaine is a non-toxic inorganic arsenic form that comes from fish and seafood.
Finding measurable amounts of arsenic in urine does not mean those levels cause an adverse health effect. Biomonitoring studies on levels of arsenic provide physicians and public health officials with reference values. These reference values help experts determine if people have been exposed to higher levels of arsenic than are found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.