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Research paper topic: Arsenic - 1749 words
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Arsenic Element 33: Arsenic Abstract Arsenic is element 33 on the periodic table and is in Group 15. Arsenic is obviously an extremely poisonous element; however, some people have found arsenic to have a restorative effect on them. Chemically, arsenic is a metalloid. Two common forms of arsenic are gray and yellow. (see Figure 1-A) Element 33 has an atomic weight of 74.9216 and the chemical symbol of As.
It boils at 613C, melts at 817C, and has a density of 5.72. (see Figure 2-A) The element has been known for centuries and can be easily obtained from ores such as arsenopyrite (FeAsS), realgar (As2S2), orpiment (As2S3), and arsenic trioxide (As2O3). There are many uses for arsenic. Among them is in the manufacturing of glass to eliminate the air bubbles and the green color caused by contaminated iron compounds. Arsenic is also added to materials such as lead and copper alloys to increase the strength and better the corrosion resistance. Although it is well known that arsenic is often used in tales (both true and otherwise) as a killing agent, arsenic has been used as a curative as well. Before penicillin was introduced, arsenic played a significant role in the treatment of syphilis. Other good uses for element 33 are as insecticides and semiconductors.
Gallium arsenide (GaAs) is a known semiconductor that is also used as a laser material. A good test for the detection of arsenic is the Marsh test, invented by James Marsh, an English chemist. Introduction Arsenic is a rather notorious element. Mystery lovers know it as the poison and in the past, it has been one of the favored choices of criminals. (Bodin and Cheinisse 1970) Arsenic compounds have been known in the world since the 4th century BC, though it wasn't described as an element until 1649.
The ancient Romans knew of arsenic because it is a by-product of several ores they used: copper, zinc, tin, lead, and gold. (Schroeder 1974) Arsenic has many uses throughout the world. China is the largest producer of arsenic metal and arsenic trioxide. The United States is the largest consumer of the product, according to 1996 statistics. In fact, the United States attributed to about two-thirds of the world's demand. All of the arsenic required by the United States was imported.
America had ceased the production of arsenic since 1985. Arsenic can be prepared in its pure form by heating arsenopyrite. It can also be found as by-products of other ores during smelting. (Edelstein 1996) Many people, when they think of arsenic, think of the element as a deadly and dangerous poison. And so it is. However, it is rarely come upon nowadays in clinical practice. Inorganic arsenicals are more likely to cause poisoning then arsenic derived organically. Arsenic is often used in products such as weed killers, insecticides, and rodenticides. Ingestion of any of these can cause severe poisoning.
Most of the toxic effects of arsenic are on the digestive system, such as burning gastroenteritis. It can also cause hypotension and circulatory collapse in the cardiovascular system, and headaches and weak muscles in the nervous system. Victims of arsenic poisoning may also experience blood in their urine. Of course there are treatments for arsenic poisoning, but it is imperative to first make sure that arsenic is the cause of the poisoning because the treatment can be just as hazardous. (Matthew and Lawson 1970) Element 33, otherwise known as arsenic, is arguably one of the most well known elements in the world. At the same time, its properties and uses are considerably less known. Arsenic is the 20th most common naturally occurring element.
It is present in all humans and is an easily obtainable poison. This element is also used in the production of ceramics, enamels, paint, wallpaper, glass, insecticides, pesticides, and rat poisons. (Turkington 1994) Arsenic also strengthens lead in batteries and improves copper alloys' resistance to corrosion. (Edelstein 1996) The electron configuration of arsenic is 2-8-18-5. (see Figure 3-A) (Web Elements 1998) In addition, it is a metalloid, meaning that it has characteristics of both metals and nonmetals. There are two valence states for arsenic: the pentavalent form and trivalent form. The pentavalent for is generally nontoxic and is organic.
Though it seldom causes habitual poisoning, organic arsenic is potentially able to do it. The trivalent form of arsenic, such as arsenic trioxide, is inorganic and highly toxic. However, there are certain ambiguities about the trivalent form. In some cases, arsenic trioxide has been shown to have curative effects. (Arena 1986) Though most people know that arsenic can kill, less know of its curative aspects. Arsenic was used in the treatment of syphilis before the introduction of penicillin.
(Arena 1986) In other clinical uses, arsenic has been replaced by antibiotics and sulfa drugs. In recent years, a new curative effect of arsenic had been reported. A group of researchers in Shanghai, China had discovered ten years ago a remedy for acute promyelocytic leukemia (APL) that had previously been fatal. They found that all-trans-retinoic acid (ATRA) was a strong combatant against APL. Now, they have found what seems to be an even more potent drug against APL in a traditional Chinese cure-all. (Mervis 1996) The story started 25 years ago when a group of doctors from the Harbin Medical University, including Zhang Ting-Dong, were sent into northeast China to gather proof of Mao Tse-Tung's belief that classical Chinese medicine was superior to Western methods. There, Zhang found that arsenic trioxide was the hidden component in the cure for arthritis, skin diseases and other illnesses.
Though arsenic trioxide can produce alarming side effects, it is relatively safe when administered in small doses, intravenously. The researchers isolated the arsenic trioxide from the traditional Chinese remedy and tested it against various cancers. It was found to have worked extremely well against APL and in one case, 14 out of 15 terminal APL victims realized complete remissions when treated with arsenic trioxide. (Mervis 1996) The way arsenic trioxide works is still under scrutiny, but it appears to act very differently from ATRA. ATRA does not kill APL cells. Instead, ATRA keeps the cell from dividing unchecked.
Arsenic trioxide, according to the journal Blood, stimulates cell death in an APL cell line. Arsenic trioxide, though it does not get rid of all leukemic cells, does allow patients to benefit from remissions lasting for 18 months or more. Some have been cancer free for 20 years. Complete remission from APL has been accomplished for about 70% of the patients. (Mervis 1996) Despite its virtues, arsenic is a deadly element. As of now, the chief problem with arsenic is its contamination of groundwater throughout the world because it is present throughout the earth's crust.
(Turkington 1994) The slightest amount of this tainted water can lead to cancer and as of now, over 700 hazardous-waste sites in the U.S. are contaminated with arsenic. Health officials wish to remove the arsenic from the soil and water, but are unable to do it until they understand how the element reacts with environment and how its compounds alter over time. (Brown 1997) Professor Hemond and students at the Massachusetts Institute of Technology have been studying how arsenic moves within the Aberjona Watershed ecosystem north of Boston. They use an instrument that quickly identifies various layers of soils and sediments. (see Figure 4-A) This allows the researchers to predict possible paths for water laced with arsenic.
They have found that arsenic there frequently alternate between two compounds: arsenate and arsenite. Arsenite is extremely toxic and highly soluble in water, thus making it easier for humans to ingest it. Arsenate, on the other hand, is less toxic and does not dissolve as easily. The students have also discovered a microbe that consumes arsenate and releases arsenite. (See figure 5-A) Another student has also found a bacterium that does the opposite by converting arsenite to arsenate. They hope to use these microorganisms to help clean up arsenic contamination.
(Brown 1997) Other studies have led toxicologists to suggest lowering the federal limit of 50 parts per billion to two parts per trillion. This is especially recommended for California because of the high concentration levels of arsenic here. (Turkington 1994) Some experts, however, dispute the idea that arsenic causes cancer, namely bladder cancer due to drinking arsenic tainted water. Studies have been done in Taiwan where the water is naturally contaminated with high levels of arsenic. The studies concluded that the tainted water could be linked with an acutely heightened chance for bladder cancer.
Although this study has aroused concern in the United States, because bladder cancer is among the nine most prevailing cancers in America, some have pointed out that the risk may be overestimated. There is the possibility of other contributing factors to the cancer such as an underlying genetic vulnerability to the cancer, the malnutrition endemic in arsenic-tainted Taiwan, and the presence of other water pollutants. (Raloff 1966) A new study, however, seem to strengthen and prove the idea that arsenic is directly linked with bladder cancer. The study was conducted in Crdoba, a province in Argentina whose water is without the additional pollutants such as in the case of Taiwan. In addition, the inhabitants of the province have an ethnic background similar to the United States and a low occurrence of malnutrition.
The study was led by Claudia Hopenhayn-Rich from the University of California, Berkeley. The water in Crdoba has high levels of naturally occurring arsenic and the residents there have a bladder cancer rate about twice as high as Argentina's average. (Raloff 1996) India is another area of major concern. Over a million Indians in West Bengal have been drinking water contaminated with high concentrations of arsenic. (see Figure 6-A) Around 200,000 people have been diagnosed with skin lesions due to arsenic.
Many of them have hardened strips of epidermis called hyperkeratoses that may potentially develop into cancers. (see Figure 7-A) It is very probable that tens of millions more can be in danger in areas that have not been tested for arsenic. Attention was first drawn to West Bengal in the 1980s when cases of poisonings were reported. The extent of the problem was far more widespread then was at first thought. (Bagla and Kaiser 1996) Dipankar Chakrabortik, a chemist from the School of Environmental Sciences at Jadavpur University, has been conducting studies on the problem for over ten years.
His team have tested 20,000 tube wells and found that 62% of them contained levels of arsenic higher than is allowable by the World Health Organization (WHO). Samples from the inhabitants' hair, urine, skin, and nails have shown that they had ingested large amounts of arsenic over the years. Many experts of ...
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