Selenium & compounds: Environmental effects
Description
Trace amounts of selenium are essential for animals, but selenium is generally not essential for plants. Many plants are selenium tolerant. The toxicity of selenium depends on whether it is in the biologically active oxidised form. This form can be found in alkaline soils, causing plant uptake of the metal to be increased. Various plants are known to accumulate selenium. The biological availability appears to be reduced in acidic or neutral soils. Some plants and micro-organisms can volatilise selenium from soils by converting selenium to volatile alkylated selenium compounds. Plants containing high levels of selenium and selenium compounds can be toxic to grazing livestock. "Blind staggers" disease is a disease in livestock that results from acute consumption of plants high in selenium. It is characterised by impaired vision, aimless wandering behaviour, reduced consumption of food and water, and paralysis. "Alkali disease" is a disease in livestock resulting from chronic consumption of high levels of selenium. It is characterised by hair loss, deformation and sloughing of the hooves, erosion of the joints of the bones, anaemia, and effects on the heart, kidney, and liver. In waters containing elevated levels of selenium fish can bioaccumulate selenium, building up high levels. Selenium and its compounds have high acute toxicity to aquatic life and mammals and moderate acute toxicity to birds. Insufficient data are available to evaluate or predict the short term effects of selenium on plants.
Entering the environment
Selenium can be transported as particles released into the atmosphere or as dissolved compounds in natural waters.
Where it ends up
Small selenium particles in the air settle to the ground or are taken out of the air by rain. Soluble selenium compounds can be found in natural waters, either as selenites or selenates.
Environmental guidelines
Australian Water Quality Guidelines for Fresh and Marine Waters: (ANZECC, 1992):
Maximum of 5 microgram/L (i.e. 0.000005 g/L) and 70 microgram/L (i.e. 0.00007 g/L) in marine waters respectively.
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