Arsenic is a natural element which behaves like a metal. It is present in the environment both naturally and due to certain human activities. It has many different forms. It can exist in inorganic or organic form, inorganic arsenic being generally considered more toxic. Arsenic is found in the natural environment in some abundance in the Earth’s crust and in small quantities in rock, soil, water and air. It is present in many different minerals. About one third of the arsenic in the atmosphere comes from natural sources, such as volcanoes, and the rest comes from man-made sources. Due to natural geological contamination, high levels of arsenic can be found in drinking water that has come from deep drilled wells.
Industrial processes such as mining, smelting and coal-fired power plants all contribute to the presence of arsenic in air, water and soil. Environmental contamination also occurs because it is used in agricultural pesticides and in chemicals for timber preservation. Environmental levels of arsenic vary. In air, levels are lowest in remote and rural areas, higher in urban areas, and highest close to industrial sources. In water, levels of arsenic are lowest in seawater, higher in rivers and lakes and highest in water from underground areas containing volcanic rock or arsenic-rich mineral deposits. The background levels of arsenic in soil and sediment increase if there are natural and/or man-made sources of arsenic contamination present.
The amounts of arsenic found in living animals, plants and microbes vary. The quantities depend on the level of local contamination and on the type of organism, as certain organisms tend to accumulate arsenic in their bodies. Arsenic is generally present in sea-living animals at higher levels than in freshwater animals, or plants and animals that live on land. Plants on land can accumulate arsenic compounds via uptake from soil and/or deposition from air onto leaves.
Living organisms, both on land and in water, react in a variety of ways to arsenic exposure. The effects depend on the chemical form of the arsenic, the nature of the surrounding environment and their own particular biological sensitivity. Individual organisms or whole populations may be affected. Adverse effects include death, poor growth and failure to reproduce. Where arsenic has contaminated a natural environment, the number of different species found is much reduced. Humans are exposed mainly through food and water. Food is usually the largest source except in areas where drinking water is naturally contaminated with arsenic. The quantities of arsenic breathed in by non-smokers are very small, except in industrially polluted areas. Smokers inhale more because arsenic is one of many hundreds of chemicals present in cigarette smoke. Exposure to arsenic in the workplace can be quite high, but the amounts present in the air in the workplace are controlled in many countries.
When arsenic is inhaled due to its presence in airborne particles, the amount absorbed into the blood stream depends on two things – how soluble the particular form of arsenic is and how small the particles are. Most arsenic in the body comes from the diet. In the gut, soluble arsenic compounds present in food are rapidly absorbed into the blood stream. Many arsenic compounds are quickly transformed and eliminated from the body via the urine. However, there are differences from one person to another in the ability to get rid of arsenic compounds.
Arsenic can have adverse effects and forms of arsenic are more toxic than others. The consequences include death when exposures are high enough to cause poisoning and cancer. Many parts of the body may also be damaged by arsenic, including the skin, gut, lungs, heart, blood vessels, immune system, urinary system, reproductive organs and the nervous system. Arsenic can also damage chromosomes, which contain the genetic material inside the cells of the body.
If a large amount of arsenic is swallowed by humans, in a form that is readily absorbed, it can cause rapid poisoning and death. The gut, the heart and the nervous system are affected. Those who survive acute poisoning may develop pigment spots in the skin and damage to red blood cells, bone marrow (where blood cells are made), liver, nerves and brain. Long-term exposure to high levels of arsenic in drinking water can cause thickening and pigment spots in the skin, and cancer of the skin, lungs, bladder or kidney. Exposure in the workplace – mainly via the air breathed in – can cause lung cancer. Smoking further increases the risk.
Long-term ingestion of arsenic, mainly from drinking of contaminated well water, has caused a disease called "Blackfoot disease" in Taiwan. Blood vessels of the leg and foot become damaged, resulting in coldness, loss of feeling and eventually gangrene in the foot.
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