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160 X.-Z. Yu and J.-D. Gu

are water soluble, and therefore they possess greater bioavailability compared
with other non-water soluble species of Se (Terry et al. 1992; Zhang and Moore
1997; Barceloux 1999; Shardendu et al. 2003; Banuelos and Lin 2005; Banuelos
et al. 2005).

9.1.1 Anthropogenic Inputs of Selenium

One of the primary anthropogenic activities responsible for mobilizing Se in the
ecosystem is the waste materials generated due to burning of fossil fuel like coal
and petroleum oil during electric power production (Lemly 1985), which is almost
1,250 times higher than that in raw coal (Pillay et al. 1963). Due to the growing
consumption for energy, more Se has been released or produced from the power
industry globally. It is estimated that more than 1,600 tons of Se has been produced
annually from mining production (Newland 1982; Nriagu and Pacyna 1988),
accounting for 80 % of the total Se produced (Haygarth 1994). Se is also produced
by oil refinery industry. Cure oil contains significantly higher concentrations of Se
than coal, and procurement and refinery of oil produce huge volume of Se-laden
wastes (Ohlendorf and Gala 2000; Simmons and Wallschla ¨ger 2005).
Selenium is widely used for a range of commercial products like glass and
ceramics. Apart from huge utility in glass industry (approximately 20 % of its
overall industrial use) (Newland 1982; Haygarth 1994), Se is also used in industries
related to photoelectric cells, pigments, rectifiers, semiconductors, steel, and
chemicals for photography and rubber vulcanizing (Barceloux 1999; Haygarth
1994). Additionally, Se is used in pharmaceutical industry for treating dandruff
and fungal infection (Haygarth 1994).

9.1.2 Fate and Transport of Selenium in the Environment

The environmental fate and transport of Se depend on, in part, the rates and
intermediates of the dynamic interconversion among the Se family, and in part the
physical transfer of Se among the different environmental compartments (Wang and
Gao 2001). It is known that there are substantial differences in the concentration,
rates, extent, and speciation of Se in various environmental media (Porcella et al.
1991). Four different organic volatile forms of Se have been detected in air, namely
methaneselenol (CH 3 SeH), dimethyl selenide (CH 3 SeCH 3 ), dimethyl selenenyl
sulfide (CH 3 SeSCH 3 ), and dimethyl diselenide (CH 3 SeSeCH 3 ) (Chasteen 1998).
Dimethylselenide (DMSe) is the most significant contributor to environmental Se
mobility through air (Karlson et al. 1994). Other inorganic atmospheric Se species,
such as hydrogen selenide (H 2 Se), elemental Se, and selenium dioxide (SeO 2 ), can
also be identified (Wen and Carignan 2007). Because Se can be released from
various sources, speciation of atmospheric Se is highly variable and unstable.