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ARSENIC

M. FEROZE AHMED, BANGLADESH UNIVERSITY OF ENGINEERING & TECHNOLOGY

Arsenic was known to me as a homeopathic medicine from my boyhood. I learned that arsenic is a poison but in small doses builds resistance against the common cold, asthma, coughs, scabies, and a variety of other diseases. My chemistry teacher then introduced arsenic as the third element in Group VA in the periodic table. The presence of arsenic in lethal doses in food, water, or air is not noticeable to human senses of sight, smell, and taste, which makes arsenic a perfect homicidal and suicidal agent. In the late 1980s, I further studied the element while deriving environmental quality standards for Bangladesh, but my understanding was limited to its evil reputation as a poison and its inhibitory effects on biological activities.

Arsenic is a ubiquitous element in nature and is widely distributed in air, water, soils, rocks, plants, and animals in variable concentrations. It is the 20th most abundant element in Earth's crust and the 12th most abundant element in the biosphere. The cycling of arsenic in the environment is regulated by natural processes and human activities. Thus, humans all over the world are exposed to small amounts of arsenic, mostly through food, water, and air.

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POISONED Arsenic contamination of drinking water is wreaking havoc in Bangladesh, prompting many scientists such as Bibudhendra Sarkar to help.
But the presence of high levels of arsenic in groundwater, the main source of drinking water in many countries around the world, has drawn the attention of the scientific community. As an environmental engineer with an interest in water supplies, I became fully involved in arsenic research in 1995. My international links with Massachusetts Institute of Technology, the University of Cincinnati, Columbia University, and the United Nations University in Japan helped me to conduct intensive work on arsenic-release mechanisms in groundwater, arsenic removal technologies, and the fate of arsenic in the environment. In addition, I extensively studied the status of arsenic problems in Bangladesh and regional countries; participated in, as well as organized, several international events; conducted advanced training on arsenic; and edited, published, and distributed five documents on arsenic, most of which are available free online.

The status of arsenic changed in 1987 when inorganic arsenic present in drinking water was classified as carcinogenic. Arsenic is known to be nonessential for plants but an essential trace element in several animal species, while its presence in humans is an issue of debate. On the basis of an epidemiological study conducted in Taiwan, arsenic content in drinking water associated with an excess lifetime skin cancer risk of 10–5 was calculated to be 0.17 mg per L--too low for measurement. The joint Food & Agriculture Organization of the United Nations/World Health Organization (WHO) Expert Committee on Food Additives confirmed a provisional tolerable weekly intake of 15 mg per kg of body weight for inorganic arsenic in 1988. WHO, therefore, recommended a provisional guideline value of 10 mg per L for arsenic in drinking water in 1993, which has been adopted as a standard for arsenic in drinking water in many developed countries. Many developing countries, including Bangladesh, for technical and economical reasons, have retained the earlier WHO guideline value of 50 mg per L as the national standard or as an interim target. The estimated number of people exposed to arsenic exceeding 50 mg per L from drinking water in Bangladesh, India, China, and Nepal is 29 million, 5.3 million, 5.6 million, and 0.6 million, respectively. Concerns have been raised about arsenic contamination in the food chain through irrigation with contaminated water.

I have visited various places in Bangladesh, India, Pakistan, and Nepal; lectured on arsenic; and exchanged views with the regional scientists. Thousands of arsenicosis cases have been confirmed in Bangladesh and West Bengal. The common adverse effects of chronic arsenic exposure are melanosis, keratosis, hyperkeratosis, some cases of skin cancer, gangrene, peripheral vascular disorder, and other adverse health effects. Fortunately, the arsenicosis prevalence rate is still much lower than the estimated risk at the present level of contamination. The poorest people are most likely to be worst affected by arsenicosis, not only physically, but also socially and economically. My present activities at the government and nongovernment levels are targeted toward providing sustained access to arsenic-safe drinking water.

Much remains to be learned about arsenic. The interindividual variation in susceptibility to arsenic toxicity is still a puzzle. The precise mechanism of action of arsenic in human systems is yet to be fully understood. The silent presence of arsenic in the environment, particularly in drinking water and the food chain, is a potential threat to humankind and deserves greater attention from the scientific community around the world.


M. Feroze Ahmed is a professor of civil/environmental engineering at Bangladesh University of Engineering & Technology, Dhaka. He received the Dr. Rashid Gold Medal in 2001.

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ARSENIC AT A GLANCE
Name: From the Greek arsenikon, yellow orpiment (a powdered pigment).
Atomic mass: 74.92.
History: Arsenic compounds were mined by the ancient Chinese, Greeks, and Egyptians. The element was first isolated by Albertus Magnus, a German alchemist, in 1250.
Occurrence: Occasionally found as a free element, but mostly it is found in a number of minerals.
Appearance: Either yellow or steel gray, very brittle crystalline, nonmetal solid.
Behavior: Arsenic is stable in dry air. Its gray form tarnishes and burns in oxygen. Arsenic salts and arsine gases are poisonous. Arsenic is carcinogenic and possibly teratogenic.
Uses: In alloys, arsenic is used in semiconductors, pesticides, wood preservatives, and glass. It is also used in bronzing.

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