**1. Introduction**

180 Pesticides in the Modern World - Risks and Benefits

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42.

Arsenic (As) is a naturally occurring ubiquitous element. It is found in the environment in the earth crust and quantities in media such as soil, water, rock and air. It is present in the environment naturally and due to human activities and other industrial processes such as mining and coal-fired power plants. Arsenic has also been used as a pesticide to protect animals, wood, fruit and vegetables from insects. Because of its therapeutic properties, arsenic has also been used as a medicinal agent. The dark side of the medicine was the reputation as an attractive poison

Arsenic is mainly transported in the environment by food, except in areas with high levels of arsenic in the drinking water e.g. India, Taiwan and Bangladesh (2004; Singh, Kumar, and Sahu 2007). The outbreak of As was triggered by deep drilled wells and the desire to obtain microorganism-free safety drinking water. Arsenic contamination of drinking-water is a hazard to human health. Because of the toxicities and side effects of arsenic compounds it is known as a major environmental pollutant. The IARC classified arsenic and arsenic compounds as a human carcinogen (Group 1) (2004). But although arsenic compounds have been known and used for centuries, their mechanisms of interaction in humans are not fully elucidated.

The paradox of arsenic compounds is that, on the one hand, they are considered extremely dangerous for human health with acute and chronic adverse health effects. Long-term arsenic exposure can lead to several types of cancer. The exposure to As has been associated also with non-carcinogenic effects e.g. such diabetes and cardiovascular diseases. On the other hand arsenic compounds are regarded as potential drugs against cancer and ranging from the use as poisons to applications in semiconductors and pesticides. Especially the discovery of organoarsenicals for the treatment of hematological malignancies and solid tumor has awakened interest.

### **2. Background and basics**

Arsenic is a chemical element in the period table that has the symbol "As", the atomic number 33 and an atomic mass of 74,92159 g/mol. Arsenic exhibits both metallic and non-metallic properties. Arsenic exists as unstable oxides and sulfides or as arsenites or arsenates of sodium, calcium and potassium. Arsenic has two biologically important oxidation states: arsenite (the trivalent form, As III) and arsenate (the pentavalent form, As V). As III is 60 times

Arsenic – Pesticides with an Ambivalent Character 183

Arsenic compounds have no smell or taste, but heat can cause As to sublimate to gas with a

Arsenic naturally occures in the earth´s surface, mostly in inorganic form (Hine, Pinto, and Nelson 1977). It exists in low concentrations in many rock types but is frequently associated with metal ore deposits e.g. Au (gold) , Ag (silver), Cu (copper) and Fe (iron) (Gochfeld 1997). The most important natural sources of arsenic in the environment are volcanoes. The

organic form result when arsenic combines with carbon and hydrogen.

Arsenic 7440-38-2 As Arsenic trioxide 1327-53-3 As2O3 Arsenic pentoxide 1303-28-2 As2O5 Arsenic sulphide 1303-33-9 As2S3

**Compound CAS No. Molecular formula** 

Dimethylarsinic acid (DMA) 75-60-5 (CH3)2AsO(OH) Potassium arsenate 7784-41-0 KH2AsO4 Potassium arsenite 10124-50-2 KasO2HAsO2

Arsenic and arsenic compounds are known since the ancient times. As early as 500 B.C. the ancients knew about arsenic, whose name comes from the Greek word "arsenikon" for potent or bold, which means orpiment form Latin auripigmentum. In the 16th an 17th centuries, red and white arsenic were put into amulets that were worn around the neck and close to the heart to ward off the plaques (Cullen 2008). Most arsenic is found in conjunction with sulfur in minerals such as arsenopyrite (AsFeS). Because of the association with ore and the stability of As in form like AsFeS, As was used as a "pathfinder element" in

distinctive garlic odor (Jones 2007).

Table 1. Physiochemical properties (1980)

geochemical exploration for gold (Jones 2007).

Fig. 2. Acidum Arsenicosum Anhydricum bottle, Global Antiques

**3. History** 

more toxic than As V (Yousef, El-Demerdash, and Radwan 2008). From biological and toxicological view, arsenic compounds can be classified into three major groups: Inorganic arsenic compounds, organic arsenic compounds and arsine gas (Hardman et al. 1996). The metalloid is found mostly as yellow complex sulfides. Organic arsenic is non-toxic whereas inorganic arsenic is toxic. The inorganic forms of arsenic are yellow (AS2S3, orpiment), red (AS2S2 realgar) and grey to silver white (FeAsS, arsenopyrite) (Waxman and Anderson 2001).

Fig. 1. Orpiment, realgar and arsenopyrite - from left to right- (Photographs from the Ohio State University Newark)

Arsenic compounds have no smell or taste, but heat can cause As to sublimate to gas with a distinctive garlic odor (Jones 2007).

Arsenic naturally occures in the earth´s surface, mostly in inorganic form (Hine, Pinto, and Nelson 1977). It exists in low concentrations in many rock types but is frequently associated with metal ore deposits e.g. Au (gold) , Ag (silver), Cu (copper) and Fe (iron) (Gochfeld 1997). The most important natural sources of arsenic in the environment are volcanoes. The organic form result when arsenic combines with carbon and hydrogen.


Table 1. Physiochemical properties (1980)
