ARSENIC IN ENVIRONMENT: PAST, PRESENT AND FUTURE

In the past, arsenic was commonly used as a poison to kill rodents, insects, and plants. Although it is rarely used today as a human poison, arsenic in the environment has become a public health concern in many parts of world. Everyone has daily exposure to arsenic because it is a naturally occurring chemical element that is normally found in small amounts in water, soil, indoor house dust, air, and food. Arsenic in groundwater and its fate and transport in the environment have become matters of great concern in Bangladesh, India, Taiwan and several other countries.

The tubewell water extracted from shallow aquifers is the primary source of drinking/cooking. The arsenic in groundwater water can undergo transformation through redox or microbial processes, adsorption-desorption and thus become retained onto soil, and be taken up by plants, and subsequently enter into the food chain. As a result, a cumulative accumulation of arsenic in surface soils is expected and arsenic concentration as high as 83 mg/kg in topsoil, against a background concentration of 4-8 mg/kg. In rice irrigated with water containing 8 mg/L arsenic accumulated 0.6 mg/kg of arsenic in grain and as high as 100 mg/kg of arsenic in straw. A relatively higher concentration of arsenic has been found in leafy vegetables; the concentration of arsenic in vegetable/food in has been found to be 20 mg/kg. It should be noted that very little is known about the chemical forms of arsenic (e.g., inorganic and organic) in crop/vegetable, which in turn is needed for estimating its toxicity. The people are drinking arsenic-contaminated groundwater and vegetable/food, and amongst them show arsenical skin lesions. There are the most commonly observed symptoms of chronic arsenic poisoning are melanosis, hyperkeratosis.

The occurrence of elevated arsenic in groundwater is generally associated with natural biogeochemical reactions such as reductive dissolution of iron oxides/hydroxides by altering groundwater redox state and releasing arsenic from sediment to aqueous phase. Also, microbes in organic-matter environment are acting as the major electron acceptor in groundwater to release arsenic.

More studies are needed to develop a better picture of arsenic transport and accumulation in the food chain.