Читать книгу Selenium Contamination in Water - Группа авторов - Страница 50

Weathering is the primary natural process to release Se in the soil. In different forms, Se present in the soil like elemental selenium, calcium selenate, basic ferric selenite, and organic selenium compounds after the decomposing of animal and plant materials. The coal‐mining region mainly contains a higher level of Se due to the presence of pyrite oxidation (Dreher and Finkelman 1992). The level of Se varies from states to states, country to country (Dhillon and Dhillon 2003; Lenz and Lens 2009). Usually, the soil contains 0.1–2 mg Se/kg (Fishbein 1983). It was found that soil in the US, India, and Ireland has a higher level of Se (100 mg Se/kg), while soil in Brazil and Argentina has a relatively lower level of Se (< 0.1 mg/kg) (Dhillon and Dhillon 2003; Lenz and Lens 2009). Depending on the higher and lower levels, one region may recognize each as a region that is seleniferous and nonseleniferous. Soil which contains 5 mg/kg Se is very toxic (Rogers et al. 1990).