Selenium pollution can arise from mining and industrial activities, also from the improper use or disposal of products containing selenium, which may include insecticides, electronic components and radiographic materials. Certain plants are known to accumulate selenium when grown in soils containing a high natural content of this element or where selenium has entered the soil from industrial waste.
In certain areas (such as parts of the mid-Western USA) some plants (for example, loco-weed) accumulate selenium to such an extent that grazing animals display toxic symptoms.
Cereals such as wheat can accumulate up to 30mg/kg without impairment of growth. It is thus possible for food crops to be contaminated by selenium.