ARSENIC RESEARCH AND DEVELOPMENT PROJECT
What is arsenic?
Arsenic is a grey-appearing chemical element (atomic number 33, symbol As in the periodic table) also termed a metalloid. Arsenic can exist in a metallic state in three forms (yellow, black, and gray; with gray predominating) and in ionic forms. Arsenic is considered to be a heavy metal, and arsenic toxicity shares some features with poisonings by other heavy metals. Historically, arsenic has been used as a medicinal agent, a pigment, a pesticide, and an agent with intent to harm (use with criminal intent). Up until 2003, arsenic (in the form of chromated copper arsenate) was used in the US as a treatment to prevent insect infestation of wood used in building. In 2003 the use of this compound was banned by the US Environmental Protection Agency. Arsenic is mixed with copper or lead to strengthen alloys containing these materials. Arsenic and some of its compounds react with proteins, mainly the thiol portions, and uncouples the process of oxidative phosphorylation, thus inactivating most cellular functions. Consequently, arsenic and some of the substances it combines with are deadly poisons to most biologic systems, except for a few bacterial species. Arsenic is used in making insecticides and weed killers. Arsenic is also thought to be carcinogenic, meaning that it has the potential to cause cancer. Arsenic can be found as a contaminant in food and water sources. Shellfish and other seafood, as well as fruits, vegetables, and rice; are the foods most commonly contaminated. Arsenic poisoning typically occurs as a result of industrial exposure, from contaminated wine or illegally distilled spirits, or in cases of malicious intent.
What is inorganic arsenic?
Inorganic arsenic is metallic or a metalloid element that forms a number of poisonous compounds. In industry, it can be found in a gaseous form termed arsine gas that is very toxic when inhaled. Inorganic arsenic is found in nature at low levels mostly compounded with oxygen, chlorine, and sulfur. These are called inorganic arsenic compounds. Inorganic arsenic compounds are much more poisonous to most biologic systems (animals, plants, humans) than organic arsenic (see below). Inorganic arsenic occurs in nature in the soil, copper and lead ore deposits, and water, but usually in low concentrations. However, it can become more concentrated when industrial processes use it to make wood preservatives, metal compounds, or organic arsenic-containing compounds such as insecticides, weed killers, and other compounds. If such compounds are burned, inorganic arsenic can be released into the air and later settle on the ground or in water and either remain in the inorganic form or combine with organic material. What is organic arsenic? Organic arsenic is any compound that is made from a chemical combination of the element arsenic with any organic compound (compounds containing a large amount of carbon). These are often termed arsenical organic compounds. Most frequently organic arsenic is a component used in making insecticides and weed killers and other compounds. Organic arsenic usually is not poisonous to humans but may be poisonous to humans in high concentrations. In general, organic arsenic is usually far less poisonous than inorganic arsenic.
Scope of the Problem
- Because of the delayed health effects, poor reporting, and low levels of awareness in some communities, the extent of the adverse health problems caused by arsenic in drinking-water is unclear and not well documented. As a result there is no reliable estimate of the extent of the problem worldwide. WHO is presently collecting information in order to make such an estimate.
- Case reports on the situation in various countries have been compiled and the arsenic problem in Bangladesh in particular has prompted more intensive monitoring in many other countries. In Bangladesh, 27 % of shallow tube-wells have been shown to have high levels of arsenic (above 0.05mg/l).
- It has been estimated that 35 – 77 million of the total population of 125 million of Bangladesh are at risk of drinking contaminated water (WHO bulletin, volume 78, (9):page 1096). Approximately 1 in 100 people who drink water containing 0.05 mg arsenic per liter or more for a long period may eventually die from arsenic related cancers.