Arsenic is a chemical element with symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but only the gray form is important to industry.
The primary use of metallic arsenic is in alloys of lead (for example, in car batteries and ammunition). Arsenic is a common n-type dopant in semiconductor electronic devices, and the optoelectronic compound gallium arsenide is the second most commonly used semiconductor after doped silicon. Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, and insecticides. These applications are declining, however.
A few species of bacteria are able to use arsenic compounds as respiratory metabolites. Trace quantities of arsenic are an essential dietary element in rats, hamsters, goats, chickens, and presumably many other species, including humans. However, arsenic poisoning occurs in multicellular life if quantities are larger than needed. Arsenic contamination of groundwater is a problem that affects millions of people across the world.
The United States’ Environmental Protection Agency states that all forms of arsenic are a serious risk to human health. The United States’ Agency for Toxic Substances and Disease Registry ranked arsenic as number 1 in its 2001 Priority List of Hazardous Substances at Superfund sites. Arsenic is classified as a Group-A carcinogen.
Arsenic appears in three allotropic forms: yellow, black and grey; the stable form is a silver-gray, brittle crystalline solid. It tarnishes rapidly in air, and at high temperatures burns forming a white cloud of arsenic trioxide. Arsenic is a member of group Va of the periodic table, which combines readily with many elements.
The metallic form is brittle, tharnishes and when heated it rapidly oxidizes to arsenic trioxide, which has a garlic odor. The non metallic form is less reactive but will dissolve when heated with strong oxidizing acids and alkalis.
Arsenic compounds are used in making special types of glass, as a wood preservative and, lately, in the semiconductor gallium arsenade, which has the ability to convert electric current to laser light. Arsine gas AsH3, has become an important dopant gas in the microchip industry, although it requires strict guidelines regarding its use because it is extremely toxic.
During the 18th, 19th, and 20th centuries, a number of arsenic compounds have been used as medicines; copper acetoarsenite was used as a green pigment known under many different names.
Arsenic in the environment
Arsenic can be found naturally on earth in small concentrations. It occurs in soil and minerals and it may enter air, water and land through wind-blown dust and water run-off. Arsenic in the atmosphere comes from various sources: vulcanoes release about 3000 tonnes per year and microorganisms release volatile methylarsines to the extent of 20.000 tonnes per year, but human activity is responsible for much more: 80.000 tonnes of arsenic per year are released by the burning of fossil fuels.
Despite its notoriety as a deadly poison, arsenic is an essential trace element for some animals, and maybe even for humans, although the necessary intake may be as low as 0.01 mg/day.
Arsenic is a component that is extremely hard to convert to water-soluble or volatile products. The fact that arsenic is naturally a fairly a mobile component, basically means that large concentrations are not likely to appear on one specific site.
This is a good thing, but the negative site to it is that arsenic pollution becomes a wider issue because it easily spreads. Arsenic cannot be mobilized easily when it is immobile. Due to human activities, mainly through mining and melting, naturally immobile arsenics have also mobilized and can now be found on many more places than where they existed naturally.
A little uncombined arsenic occurs naturally as microcrystalline masses, found in Siberia, Germany, France, Italy, Romania and in the USA. Most arsenic is found in conjuction with sulfur in minerals such as arsenopyrite (AsFeS), realgar, orpiment and enargite. Non is mined as such because it is produced as a by-product of refining the ores of other metals, such as copper and lead.
World production of arsenic, in the form of its oxide, is around 50.000 tonnes per year, far in excess of that required by industry. China is the chief exporting country, followed by Chile and Mexico. World resources of arsenic in copper and lead ores exceed 10 million tonnes.
A metallic element that forms a number of poisonous compounds, arsenic is found in nature at low levels mostly in compounds with oxygen, chlorine, and sulfur. These are called inorganic arsenic compounds. Arsenic in plants and animals combines with carbon and hydrogen. This is called organic arsenic. Organic arsenic is usually less harmful than inorganic arsenic.
Most arsenic compounds have no smell or special taste. Inorganic arsenic compounds are mainly used to preserve wood. They are also used to make insecticides and weed killers. Copper and lead ores contain small amounts of arsenic.
When arsenic enters the environment, it does not evaporate. It gets into air when contaminated materials are burned. It settles from the air to the ground where it does not break down, but can change from one form to another. Most arsenic compounds can dissolve in water. Fish and shellfish build up organic arsenic in their tissues, but most of the arsenic in fish is not toxic.
Arsenic is a naturally occurring element widely distributed in the earth’s crust. In the environment, arsenic is combined with oxygen, chlorine, and sulfur to form inorganic arsenic compounds. Arsenic in animals and plants combines with carbon and hydrogen to form organic arsenic compounds. Inorganic arsenic compounds are mainly used to preserve wood.
Copper chromated arsenic (CCA) is used to make “pressure-treated” lumber. CCA is no longer used in the U.S. for residential uses; it is still used in industrial applications. Organic arsenic compounds are used as pesticides, primarily on cotton plants.
Arsenic is a naturally occurring element that is found in combination with either inorganic or organic substances to form many different compounds. Inorganic arsenic compounds are found in soils, sediments, and groundwater. These compounds occur either naturally or as a result of mining, ore smelting, and industrial use of arsenic.
Organic arsenic compounds are found mainly in fish and shellfish. In the past, inorganic forms of arsenic were used in pesticides and paint pigment. They were also used as wood preservatives and as a treatment for a variety of ailments. Today, usage of arsenic-containing pesticides and wood preservatives is restricted.
Symptoms of arsenic poisoning begin with headaches, confusion, severe diarrhea, and drowsiness. As the poisoning develops, convulsions and changes in fingernail pigmentation called leukonychia striata (Mees’s lines, or Aldrich-Mees’s lines) may occur.
When the poisoning becomes acute, symptoms may include diarrhea, vomiting, vomiting blood, blood in the urine, cramping muscles, hair loss, stomach pain, and more convulsions. The organs of the body that are usually affected by arsenic poisoning are the lungs, skin, kidneys, and liver. The final result of arsenic poisoning is coma and death.
Arsenic is related to heart disease (hypertension-related cardiovascular disease), cancer, stroke (cerebrovascular diseases), chronic lower respiratory diseases, and diabetes. Skin effects can include skin cancer in the long-term but often prior to skin cancer are different skin lesions. Other effects may include darkening of skin and thickening of skin.
Chronic exposure to arsenic is related to[clarification needed] vitamin A deficiency, which is related to heart disease and night blindness.
Inorganic arsenites (arsenic(III)) in drinking water have a much higher acute toxicity than organic arsenates (arsenic(V)). The acute minimal lethal dose of arsenic in adults is estimated to be 70 to 200 mg or 1 mg/kg/day.
Organic arsenic is less harmful than inorganic arsenic. Seafood is a common source of the less toxic organic arsenic in the form of arsenobetaine. The arsenic reported in 2012 in fruit juice and rice by Consumer Reports was primarily inorganic arsenic.
Drinking-water and food
The greatest threat to public health from arsenic originates from contaminated groundwater. Inorganic arsenic is naturally present at high levels in the groundwater of a number of countries, including Argentina, Bangladesh, Chile, China, India, Mexico, and the United States of America. Drinking-water, crops irrigated with contaminated water and food prepared with contaminated water are the sources of exposure.
Fish, shellfish, meat, poultry, dairy products and cereals can also be dietary sources of arsenic, although exposure from these foods is generally much lower compared to exposure through contaminated groundwater. In seafood, arsenic is mainly found in its less toxic organic form.
Inorganic arsenic is a confirmed carcinogen and is the most significant chemical contaminant in drinking-water globally. Arsenic can also occur in an organic form. Inorganic arsenic compounds (such as those found in water) are highly toxic while organic arsenic compounds (such as those found in seafood) are less harmful to health.
Arsenic is one of the most toxic elements that can be found. Despite their toxic effect, inorganic arsenic bonds occur on earth naturally in small amounts. Humans may be exposed to arsenic through food, water and air. Exposure may also occur through skin contact with soil or water that contains arsenic.
Levels of arsenic in food are fairly low, as it is not added due to its toxicity. But levels of arsenic in fish and seafood may be high, because fish absorb arsenic from the water they live in. Luckily this is mainly the fairly harmless organic form of arsenic, but fish that contain significant amounts of inorganic arsenic may be a danger to human health.
Arsenic exposure may be higher for people that work with arsenic, for people that live in houses that contain conserved wood of any kind and for those who live on farmlands where arsenic-containing pesticides have been applied in the past.
Exposure to inorganic arsenic can cause various health effects, such as irritation of the stomach and intestines, decreased production of red and white blood cells, skin changes and lung irritation. It is suggested that the uptake of significant amounts of inorganic arsenic can intensify the chances of cancer development, especially the chances of development of skin cancer, lung cancer, liver cancer and lymphatic cancer.
A very high exposure to inorganic arsenic can cause infertility and miscarriages with women, and it can cause skin disturbances, declined resistance to infections, heart disruptions and brain damage with both men and women.
- Finally, inorganic arsenic can damage DNA.
- A lethal dose of arsenic oxide is generally regarded as 100 mg.
- Organic arsenic can cause neither cancer, nor DNA damage. But exposure to high doses may cause certain effects to human health, such as nerve injury and stomachaches.
The Environmental Protection Agency limits the amount of arsenic in U.S. public drinking water to 10 parts per billion (ppb). Water that comes from privately owned wells may contain higher levels of arsenic, especially in areas where the groundwater flows over arsenic-rich bedrock, according to Dartmouth University.
- No federal limit has been set for the amount of arsenic in foods.
- Arsenic may found in grains, fruits and vegetables according to the FDA.
- Rice is different than other grains — it takes up arsenic more readily from the environment, according to the FDA.
- Some seafood also has high levels of the less-toxic form of arsenic (organic arsenic), the FDA says.
According to Consumer Reports, a 2010 study from the EPA said that vegetables account for the biggest dietary exposure to arsenic, accounting for 24 percent of intake. Fruits and fruit juices follow, with 18 percent, and rice accounts for 17 percent.
Arsenic is naturally found in groundwater. Chronic arsenic poisoning results from drinking contaminated well water over a long period of time. Many aquifers contain high concentration of arsenic salts. The World Health Organization (WHO) recommends a limit of 0.01 mg/L (10 parts per billion) of arsenic in drinking water.
This recommendation was established based on the limit of detection for most laboratories’ testing equipment at the time of publication of the WHO water quality guidelines. More recent findings show that consumption of water with levels as low as 0.00017 mg/L (0.17 parts per billion) over long periods of time can lead to arsenicosis.
From a 1988 study in China, the US protection agency quantified the lifetime exposure of arsenic in drinking water at concentrations of 0.0017 mg/L (1.7 ppb), 0.00017 mg/L, and 0.000017 mg/L are associated with a lifetime skin cancer risk of 1 in 10,000, 1 in 100,000, and 1 in 1,000,000 respectively. WHO asserts that a water level of 0.01 mg/L (10 ppb) poses a risk of 6 in 10000 chance of lifetime skin cancer risk and contends that this level of risk is acceptable.
One of the worst incidents of arsenic poisoning via well water occurred in Bangladesh, which the World Health Organization called the “largest mass poisoning of a population in history.
Mining techniques such as hydraulic fracturing may mobilize arsenic in groundwater and aquifers due to enhanced methane transport and resulting changes in redox conditions, and inject fluid containing additional arsenic.
What’s the difference between organic arsenic and inorganic arsenic?
Atoms of arsenic bond with other elements to form molecules — if carbon is one of these elements, then the arsenic compound is an organic compound. If there is no carbon present, then the arsenic compound is in an inorganic compound. (When the term “organic” is used in this way, it refers to the chemical elements present, and differs completely from the “organic” label that is applied to some foods. Both organic and conventionally-grown foods may contain arsenic, according to the FDA.)
Inorganic arsenic is a known human carcinogen — it is this form of arsenic that is linked with increased risks of cancer and other health effects.
Do we know that the arsenic in rice is harmful?
No. “It is critical to not get ahead of the science,” Michael Taylor, the FDA deputy commissioner for foods, said in a statement. “The FDA’s ongoing data collection and other assessments will give us a solid scientific basis for determining what action levels and/or other steps are needed to reduce exposure to arsenic in rice and rice products.”
Should I eat less rice?
The FDA is not currently recommending that consumers change their consumption of rice or rice products; however, the agency does say that people should eat a balanced diet containing a wide variety of grains.
Consumer Reports also recommends that people eat a varied diet, and experiment with other grains.
“Vary your grains, especially if you eat more than two or three servings of rice per week,” the organization recommends, noting that wheat and oats tend to have lower levels than rice
Dangers of arsenic
Even when there is no foul play involved, arsenic still poses a danger, as lethal levels may be leaked into people’s water, food or air supply. The most urgent concern is drinking water, and for some places, the risk of arsenic contamination is particularly high.
In 2001, the Environmental Protection Agency (EPA) adopted a lower standard for arsenic in drinking water. The new arsenic standard of 10 parts per billion (ppb) replaced the old standard of 50 ppb.
Bruce A. Stanton, a professor in the department of microbiology and immunology at the Geisel School of Medicine at Dartmouth College in New Hampshire, said that in many states, “arsenic can be found in well water at levels above the EPA standard of 10 ppb.”
“Well-water arsenic is above the EPA standard in as many as one in five wells in New Hampshire and many other states, including Maine, Michigan, California, New Mexico, Arizona, Colorado and Nevada,” he told Live Science.
As for food, the Food and Drug Administration (FDA) recently turned its attention toward rice, as it tends to absorb arsenic more readily than other crops do. And since rice is a staple in the diets of many infants and young children, the FDA has been closely monitoring rice for safety, ensuring that infant rice cereal stays under 100 parts per billion (ppb) for levels of inorganic arsenic.
One study, published in the Nutrition Journal, suggested that other types of foods, including white wine, beer and Brussels sprouts, may be linked to higher levels of arsenic in humans as well. The FDA has also taken steps to monitor apple juice.
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