Arsenic

Arsenic is a naturally occurring element (As) that is widespread in Earth's crust. It occurs in minerals, soil, water, air, and food as a result of both natural and industrial processes. Inorganic arsenic is highly toxic and the most significant chemical contaminant of drinking water worldwide.

Pure arsenic is a whitish metallic element that is rare in the environment; rather, it forms compounds with other elements. Arsenic combines with oxygen, chlorine, or sulfur to make highly toxic inorganic compounds that, along with pure arsenic, are classified as human carcinogens. Organic (carbon-containing) arsenic compounds form in plants and animals. They are generally less toxic, although the International Agency for Research on Cancer classifies dimethylarsinic acid (cacodylic acid) and monomethylarsonic acid as possible carcinogens. Fatal arsenic poisoning requires a single dose of 70 mg, but long-term exposure to far smaller amounts in drinking water and food is associated with numerous health problems, including skin lesions, cardiovascular disease, diabetes, and cancer. Arsenic can cross the placenta and enter fetal tissues and has been found at low levels in breast milk. Exposure during fetal development and early childhood can negatively affect cognitive development. However, humans may build up tolerance to arsenic's toxic effects, as evidenced by nineteenth-century Austrian mountaineers who consumed it as a stimulant.

High levels of inorganic arsenic in bedrock can seep into groundwater used for drinking and irrigation. Inorganic and organic arsenic compounds in soil and groundwater can be absorbed into grain, fruit, and vegetables. Food may be as significant an arsenic source as water, since some level can be detected in most foods and beverages. Rice absorbs arsenic more readily than other grains, primarily because it is grown in flooded conditions that separate arsenic from soil particles. Arsenic concentrates in the rice seed, a staple food throughout much of the world. By body weight, infants consume about three times more rice than adults, mostly as rice cereal. Rice-based products, such as cereal bars, energy shots, fruit juices and concentrates, and seaweed can contain inorganic arsenic. Organic arsenic accumulates in fish and shellfish but is nontoxic and readily eliminated from the human body.

Volcanoes and mining release arsenic into the environment. Tobacco smoke and burning of fossil fuels such as coal can release small amounts of arsenic into the air. Arsenic is produced as a byproduct in copper, cobalt, and lead smelting. Inorganic arsenic compounds are used in industrial processes such some glass and semiconductor manufacturing; as a lead additive in batteries; and in animal-hide preservation. In the past, many workers were exposed to high levels of arsenic fumes and dust, and it is found at the vast majority of U.S. National Priority List Superfund sites (sites that release or are likely to release hazardous substances). Arsenic has not been produced in the United States since 1985, but it is still imported from other countries. Use of arsenic-containing pesticides on U.S. cotton fields and orchards was discontinued in the 1950s, but low levels remain in the soil and can seep into water sources. Inorganic arsenic compounds have not been used in U.S. pesticides since 1993. Organic arsenic compounds were phased out in 2013, except for one product used on cotton plants.

Chromated copper arsenate (CCA) is a pesticide used as a preservative in pressure-treated wood. U.S. residential CCA use ended in 2003; however, many foundations, decks, fences, playground equipment, picnic tables, and garden-bed borders still contain CCA-treated wood, and it is still used in industrial settings. CCA may remain on the surface of newly treated wood or seep through cracks. It is watersoluble so, depending on the wood type and age, rainwater can leach it onto the surface or into soil, where it can stick to hands or clothing. Arsenic exposure can also occur from breathing sawdust or smoke from CCA-treated wood.

The biggest risk factors for arsenic exposure are drinking contaminated water and consuming foods exposed to contaminated water. Other risk factors are:

Arsenic-contaminated groundwater occurs naturally worldwide. At least 140 million people in 50 countries drink water with arsenic levels above 10 g/L or 10 parts per billion (ppb), the provisional guideline of the World Health Organization (WHO). The guideline is provisional because of the many practical difficulties in removing arsenic from drinking water, limited resources, and risks from low-arsenic water contaminated with microorganisms. In Bangladesh, 35–70 million people have been chronically exposed to arsenic, and tens of thousands die every year in what may constitute the largest mass poisoning in human history. In some areas of Bangladesh, groundwater concentrations are above 3,000 μ/L. Parts of India, Pakistan, Vietnam, China, Japan, Taiwan, Argentina, Chile, Mexico, and the United States also have high levels of arsenic in drinking water.

Most arsenic exposure is from ingesting contaminated water and food. Smokers can be exposed from tobacco that has taken up arsenic from the soil, especially in the past when tobacco plants were treated with lead-arsenate insecticide. Skin contact can cause redness and swelling, but at environmental levels, little or no arsenic is absorbed through the skin. Breathing in high levels of arsenic-contaminated dust in the workplace can cause sore throat and lung irritation.

Arsenic affects developmental processes and many organs and body systems including the skin, liver, kidneys, bladder, and prostate and respiratory, cardiovascular, nervous, immune, and endocrine systems. Very high doses of inorganic arsenic can cause shock, paralysis, delirium, and death within a few hours. Somewhat lower doses can cause headache, gastrointestinal bleeding and other symptoms, low blood pressure, loss of brain function, and death. Symptoms of longer-term, lower-level exposure include skin discoloration and small corns or warts.

Symptoms of short-term ingestion of high levels include:

Signs and symptoms of long-term arsenic exposure differ among individuals, populations, and geographical areas. In addition to the above symptoms, long-term workplace or drinking-water exposure to levels of 100–1,500 ppb can cause:

Exposure to inorganic arsenic for 20 years or more is associated with pulmonary disease; diabetes; cardiovascular disease, including heart attack; and fetal damage, infant mortality, and developmental and cognitive problems in offspring. In Taiwan, arsenic is linked to a severe blood-vessel disease called blackfoot because the feet turn black from poor circulation.

Miners and copper smelter and pesticide workers with high inhaled exposure have increased lung cancer risk and possibly increased risk of leukemias; lymphomas; and skin, stomach, and kidney cancers. People in Southeast Asia and South America drinking high-arsenic water have increased risk for bladder, kidney, lung, and skin cancers, and possibly colon, prostate, and liver cancers.

Since most arsenic is excreted in the urine within a few days, urine tests only detect recent exposure and do not distinguish between organic arsenic from fish and shellfish and more toxic forms. Specialized laboratories can measure arsenic in blood, hair, and nails. Since arsenic binds to keratin protein in slow-growing hair and nails, tests can reveal high-level exposure within the past 6–12 months. Toenail arsenic tests are most accurate because toenails are less susceptible to contamination from other arsenic sources such as soaps, shampoos, and air pollution. However, these tests do not necessarily detect low levels, and, unless levels are very high, they do not indicate future health risks. Furthermore, there is no way to distinguish cancers caused specifically by arsenic. Arsenicexposed people should have regular skin-cancer checks and possibly other early-detection tests such as for cancer cells in urine.

Beginning in the 1990s, Bangladesh's ongoing crisis awakened public-health authorities to the severity of arsenic contamination. However, it is impossible to eliminate arsenic exposure completely, and there is no consensus on what constitutes safe levels, since many studies have focused on populations with very high arsenic levels in drinking water. Thus, little is known about effects of chronic low-level exposure. As of 2018, international food-safety organizations and the U.S. Food and Drug Administration (FDA) were considering limits on arsenic in foods.

In the 1990s, WHO recognized arsenic in drinking water as a major public-health emergency, and it is one of WHO's ten chemicals of major public-health concern. Nevertheless, millions of Bangladeshis continue to drink water with arsenic concentrations exceeding the national standard of 50 μg/L, and many millions more are exposed to concentrations above 10 μg/L.

The European Commission limited inorganic arsenic in rice and rice products in 2016. As of 2018, a Code of Practice for the Prevention and Reduction of Arsenic Contamination in Rice was being compiled for producers. The European Food Safety Authority was studying infant exposure to arsenic in rice products and recommended that young children not be given rice drinks.

The EPA lowered its public drinking-water standard for all forms of arsenic from 50 ppb to 10 ppb in 2006. Some states, such as New Jersey, have more stringent standards. Nevertheless, as of 2018, there were no arsenic limits for private wells. The EPA's so-called safe limit for inorganic arsenic consumption of 0.3 μg per kg (2.2 lb.) of body weight per day, and California's daily limit of 10 μg, allow for a daily serving of most rice or rice products, without considering other exposures from food or water. For example, 2 qt. (L) daily of city water containing 5 ppb arsenic equals 10 μg. The EPA limits arsenic release from industrial sources and has eliminated or restricted many of its pesticide uses. The use of the organic arsenic compound roxarsone as a feed additive for chickens, turkeys, and pigs was discontinued in 2011 due to concerns about arsenic levels in meat and in soil fertilized with manure.

The FDA has tested total arsenic in foods such as rice and juices since 1991 and monitors some domestic and imported foods, including those likely to be consumed by children. In 2016, it proposed an inorganic arsenic limit of 100 ppb in infant rice cereal, which is close to the level in most cereals on the U.S. market, and warned that high arsenic intake during pregnancy was linked to adverse outcomes and decreased performance on certain developmental learning tasks. As of 2018, it had not limited arsenic in most foods, although bottled water was limited to 10 ppb, and the same limit was being proposed for apple juice. The relatively high concentrations in fruit juices may be due to their importation from countries where arsenic-containing pesticides are still used.

The Occupational Safety and Health Administration limits workplace exposure to 10 μg of inorganic arsenic per m³ (1.3 yd.³) of air averaged over eight-hour days and 40-hour work weeks. Personal protective gear such as respirators are required if there is a potential for higher exposure.

Arsenic levels have declined across the United States, and some arsenic-induced health problems may improve over time. However, arsenic exposure during pregnancy is associated with adverse outcomes and infant mortality. Arsenic-exposed people should attempt to reduce or eliminate other cancer risk factors, such as smoking and sun exposure. Although arsenic contamination is being more closely monitored and reduced where possible, sea-level rise from climate change is expected to increase the release of arsenic from contaminated coastal soils.

Safe water is the most important factor in preventing arsenic exposure. U.S. public-water systems are required to provide customers with annual reports on chemicals in their water. People not on public-water systems should have their water tested. If arsenic levels are above 10 ppb, they can choose to drink bottled water or, if possible, substitute rainwater or treated surface water for drinking, cooking, and irrigating. High-arsenic water can be used for bathing and washing clothes. Common household water filters do not remove arsenic effectively; it can be removed by reverse-osmosis, ultrafiltration, and ion-exchange systems, or low-arsenic water can be blended with higher-arsenic water to reduce the concentration. When safe drinking water is available, water testing, accompanied by education about arsenic contamination, has been shown to reduce arsenic exposure. Folic acid supplements can significantly reduce blood arsenic levels in chronically exposed people. It is important to not smoke and to limit contact with high-arsenic soils.

Various factors influence the amount of arsenic in rice, but the type of rice is most important. Rice growers can choose varieties that take up less arsenic, and manufacturers can use low-arsenic rice, especially in gluten-free products and those geared to young children. In general, it is believed that most people eating varied, balanced diets that include grains other than rice do not need to be overly concerned about arsenic in food, although they may choose to eat less rice. Daily servings of rice and rice products are of concern for pregnant women, infants, and toddlers.

The FDA and the American Academy of Pediatrics recommend feeding babies iron-fortified multigrain, oat, or barley cereals rather than relying solely on rice cereals. Rice milk should not be used as a dairy substitute. Research indicates that cooking one part brown rice with six to ten parts water and draining the excess water can reduce inorganic arsenic content 40%–60%, although this method is not suitable for white rice. Children should be limited to 0.5–1 cup (118–237 mL) of fruit juice per day.

Workplace arsenic exposure can be reduced or eliminated by the following:

Stores selling CCA-treated wood should provide safe-handling information sheets. Methods for reducing CCA exposure include:

See also Smoking ; Water pollution ; Water quality ; Water quality standards .