ABSTRACT
Arsenic (As) is one of the most toxic metals occurring in natural ecosystems. The major cause of human As toxicity is from contamination of drinking water from natural geological sources (Ratnaike 2003). Natural contamination of groundwater by As has become a threatening problem in many parts of the world, especially in areas where groundwater is the only or major drinking water source. However, groundwater contamination is often caused by agricultural activities, where As is used for the production of insecticides and herbicides. Areas, which are close to mining activities or smelters, have also been found to contain elevated As concentrations. Arsenic is mainly present in waters in its inorganic forms. Inorganic As occurs with two main oxidation states in natural waters, such as As(V) and As(III). Arsenates are the predominant species in oxygenated water, whereas arsenite species predominate under anoxic or reduced conditions (Fields et al. 2000). As(III) is more toxic and more difficult to be removed by the conventionally applied physicochemical treatment methods (Jekel 1994) than As(V) (Pontius et al. 1994).
