Selenium Contamination in Water. Группа авторов

2 Selenium Distribution and Chemistry in Water and Soil

       Sulaxna Sharma1 and Awanish Kumar Sharma2

       1 THDC, IHET, Tehri, Uttarakhand, India

       2 Department of Physics, GEU, Dehradun, Uttarakhand, India

2.1 Introduction

Selenium is a rarer element on earth and ranked as 70th element among naturally occurring elements in order of its natural abundance. It was first discovered by Swedish chemist Jo¨ns Jacob Berzelius in 1818 when preparing sulfuric acid. He named it after the Greek word selene (meaning “moon”). Selenium after its discovery was almost unnoticed for decades (Hamilton 2004), until the identification of its nutritional essentiality in animals in 1957 (Schwarz and Foltz 1957). The interest of researchers in the trace element has grown substantially with the recognition of its nutritional role as antioxidant and toxicity among human beings (Rotruck et al. 1973). It is dispersed widely in low concentration in the Earth’s crust (Berrow and Ure 1989; Russell 2011) and its concentrations in the Earth’s crust and sea water are 0.004 and 0.09 μg/g, respectively. However, the average global concentration of Se in soil is 0.4 μg/g (i.e. ranging from 0.01–2 μg/g) (Dungan et al. 2002) and 3.1 μg/g in soil of Northwest India (Bajaj et al. 2011). However, only bioavailable Se is the key to determine Se in plant tissues ranging from 0.02–4000 μg/g, depending upon low to high seleniferous soil, which enters into food chain. Hamilton (2004) has reported that the trace to moderate amount, i.e. 40–400 μg/day, of Se is necessary for development and normal growth, and to maintain homeostatic functions, respectively. The deficiency of Se in diet (<3 μg/day, reported by Yang et al. (1983), in China) can weaken immune system and can cause Keshan disease and Kashin–Beck disease, (Coppinger and Diamond 2001). On the other hand, a higher concentration (>400 μg/day) of it may cause health hazard to living beings, including gastrointestinal, respiratory, and cardiovascular problems. It may also result in fragile nails, excessive tooth decay, hair loss, garlic‐smelling breath, discoloration and mental problems (Pedrero and Madrid 2009). The intake of Se recommended by World Health Organization (WHO) and different recommended Se intakes followed in different countries are summarized in Table 2.1.

Table 2.1 Recommended daily nutrient requirement of selenium (μg/d) as per WHO and NAS and followed by different countries and their daily Se intakes.

      ^a WHO (2005).

      ^b National Academy of Science (NAS) (2000).

      ^c Thomson (2003).

      ^d Thomson (2004).

      ^e Keshan disease area.

      ^f Seleniferous area.

      g Data not available.

For adults, the recommended dietary allowance (RDA) is 55 μg/day (see Table 2.1) and tolerable upper intake is 400 μg/day, set by the Institute of Medicine of the National Academy of Sciences (NAS 2000) in the US, while more than 5 mg/day can be fatal (Mayer (2010). Amweg et al. (2003) has reported that excessive Se replaces the sulfur from amino acids that subsequently changes the 3D structure of proteins and impairs the enzymatic functions. Levander and Burk (2006) have discussed the biological properties of organoselenium compounds in metabolism and have reported that organoselenium compounds, i.e. di‐/trimethylselenides and selenoamino acids, viz. selenomethionine, selenocystine, and selenohomocystine compounds, are of interest in nutrition and health. Ralston et al. (2009) have reported that dimethylselenide is volatile neutral molecule and readily excreted through breathing and thus provides a natural way to export excess of Se from body. The established “no observed adverse effect level” (NOAEL) in China for human population is 15.5 μg Se/kg body weight

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