Arsenic Essay Research Paper Element 33 ArsenicAbstractArsenic — страница 2

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 (Arena 1986) In other clinical uses, arsenic has been replaced by antibiotics and sulfa drugs.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