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Chemistry science fair project:
Everything about Arsenic




Science Fair Project Information
Title: Everything about arsenic
Subject: Chemistry
Grade level: Elementary School - Grades 4-6
Academic Level: Ordinary
Project Type: Descriptive
Cost: Low
Awards: 2nd place, Canada Wide Virtual Science Fair (2004)
Affiliation: Canada Wide Virtual Science Fair (VSF)
Year: 2004
Description: Main topics: background, types of arsenic, uses, safety, exposure to arsenic in our environment, quiz.
Link: http://www.virtualsciencefair.org/2004/dewj4a0/public_html/
Arsenic Short Background

Arsenic is chemical element 33 on the periodic table. Its symbol is As.

Arsenic is an element that is known as a metalloid. It can act like a metal and a nonmetal at different times. It does not conduct electricity very well (like most metals), but it is a semiconductor. This means that arsenic can be used in computers to make them faster.

Most people know about arsenic because it is dangerous. Arsenic is toxic and can kill a person if they get too much of it. This really only happens when a person gets poisoned because there is not enough of it in our food to actually hurt us. Sometimes there is too much arsenic in water, and the government tries to make sure that it is removed before people drink the water. Even so, some people believe that we need an extremely small amount of arsenic to make sure that our body works right. We get all of the arsenic that we might need from our food.

The toxicity of arsenic to insects, bacteria and fungi makes it an ideal component for the preservation of wood. World wide the treatment with chromated copper arsenate, also known as CCA or Tanalith was the largest consumer of arsenic since the introduction of the process in the 1950s. Due to the environmental problems caused by the arsenic most countries banned the use of chromated copper arsenate on consumer products. The ban began in the European Union and in the United States in 2004.

During the 18th, 19th, and 20th centuries, a number of arsenic compounds have been used as medicines, including arsphenamine (by Paul Ehrlich) and arsenic trioxide (by Thomas Fowler). Arsphenamine as well as Neosalvarsan was indicated for syphilis and trypanosomiasis, but has been superseded by modern antibiotics. Arsenic trioxide has been used in a variety of ways over the past 200 years, but most commonly in the treatment of cancer. The US Food and Drug Administration in 2000 approved this compound for the treatment of patients with acute promyelocytic leukemia that is resistant to ATRA. It was also used as Fowler's solution in psoriasis.

After World War I the United States built up a stockpile 20,000 tons of Lewisite (arsenic trichloride reaction with acetylene in the presence of a hydrochloric acid solution of mercuric chloride); a chemical weapon, acting as a vesicant (blister agent) and lung irritant. The stockpile was neutralized with bleach and dumped into the Gulf of Mexico after the 1950s. During the Vietnam War the United States used Agent Blue a mixture of Na cacodylate) and dimethyl arsinic acid (cacodylic acid as one of the rainbow herbicides to deprive the Vietnamese of valuable crops.

Arsenic and many of its compounds are especially potent poisons. Arsenic disrupts ATP production through several mechanisms. At the level of the citric acid cycle, arsenic inhibits pyruvate dehydrogenase and by competing with phosphate it uncouples oxidative phosphorylation, thus inhibiting energy-linked reduction of NAD+, mitochondrial respiration, and ATP synthesis. Hydrogen peroxide production is also increased, which might form reactive oxygen species and oxidative stress. These metabolic interferences lead to death from multi-system organ failure (see arsenic poisoning) probably from necrotic cell death, not apoptosis. A post mortem reveals brick red colored mucosa, due to severe hemorrhage. Although arsenic causes toxicity, it can also play a protective role.

Arsenic contamination of groundwater is a natural occurring high concentration of arsenic in deeper levels of groundwater, which became a high-profile problem in recent years due to the use of deep tubewells for water supply in the Ganges Delta, causing serious arsenic poisoning to large numbers of people. A 2007 study found that over 137 million people in more than 70 countries are probably affected by arsenic poisoning of drinking water.

Approximately 20 incidents of groundwater arsenic contamination have been reported from all over the world. Of these, four major incidents were in Asia, including locations in Thailand, Taiwan, and Mainland China. South American countries like Argentina and Chile have also been affected. There are also many locations in the United States where the groundwater contains arsenic concentrations in excess of the new Environmental Protection Agency standard of 10 parts per billion.

Arsenic is a carcinogen which causes many cancers including skin, lung, and bladder as well as cardiovascular disease.

Occupational exposure to arsenic may occur with copper or lead smelting and wood treatment, among workers involved in the production or application of pesticides containing organic arsenicals. Humans are exposed to arsenic through air, drinking water, and food (meat, fish, and poultry); this food is usually the largest source of arsenic. Arsenic was also found in wine if arsenic pesticides are used in the vineyard. Arsenic is well absorbed by oral and inhalation routes, widely distributed and excreted in urine; most of a single, low-level dose is excreted within a few days after consuming any form of inorganic arsenic. Remains of arsenic in nails and hair can be detected even after years and years after the exposure.

Murder mystery stories often feature arsenic poisoning, although they commonly omit the more disagreeable symptoms.

Arsenic poisoning, accidental or deliberate, has been implicated in the illness and death of a number of prominent people throughout history.

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)

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