Arsenic and Its Compounds  

Arsenic (As) is a metalloid (semi-metal) present as a trace element throughout the environment. It is situated in group 15 or so-called Nitrogen group in the periodic table. It is supposed to be extremely toxic, mutagenic, and carcinogenic and because of these characteristics, it represents one of the most important environmental concern. Figure 1. Arsenic in the periodic table and its characteristics Arsenic can be present in four oxidations (valency) states –3, 0, +3, and +5. Arsenite (AsIII) is the main form under reducing conditions while arsenate (AsV) presents a stable form in oxygenated conditions (Gomez-Caminero, Howe and Hughes).

Arsenic presence is noted in the Earth’s crust, seawater, and in the human body in small concentrations. Natural presence in the environment is associated with geological processes such as weathering and erosion of rocks and soils which are abundant with arsenic (Faust, Chen and Kieloaho) and as a result of volcanic activity (Gomez-Caminero, Howe and Hughes) which makes geological contamination the most alarming source of arsenic (Bhattacharya and Ghosh) in some parts of the world, especially connected to South Asia. Increasing of arsenic concentrations in the environment are results of natural and anthropogenic sources (Novosel), and by the anthropogenic sources imply the use of herbicides, insecticides, desiccants, feed additives, wood preservatives, and etc. (Bhattacharya and Ghosh). In the environment, it is quite rare to find arsenic in its free (elemental) form which is not soluble in water, usually, it is found in minerals. There are more than 200 known minerals which contain a significant concentration of arsenic.

The most frequent are primary minerals such as arsenopyrite (FeAsS), realgar (As4S4), orpiment (As2S3), etc. (Bhattacharya and Ghosh). Even though the use of arsenic in therapeutic purpose is known from Roman and Greek time, credit for the arsenic isolation is ascribed to the alchemist Albert Magnus (12 – 13 century). Figure 2 In the environment, arsenic can occur in two forms, organic and inorganic. Arsenic and carbon atoms are bonded in the organic form while there are no carbon atoms in the inorganic form. Between these two types, inorganic arsenic is more abundant. It occurs with other elements such as sulfur, oxygen, and chlorine. Inorganic arsenic represents a health risk for humans and other living species which are inhabiting different environments.

Arsenic pollution of soils, sediments, and muds are the main reasons for the contamination of surface, groundwater, and the drinking water. In this way, arsenic can enter the food chain in higher and potentially toxic concentration. Today, millions of people are exposed to elevated, toxic concentrations of arsenic in food, air, water, and soil with unknown long-term consequences on their health (Bhattacharya and Ghosh) (Novosel). Presence of arsenic in the groundwater In the groundwater, arsenic is present in various concentrations all over the world. Because of its effect on the human body, the Environmental Protection Agency (EPA) set a maximum contaminant level of 10 µg/L of As in drinking water in 2006 (Rodriguez-Freire, Fiel and Sierra-Alvarez).