see also:

• foods that may be toxic or bad for you

• selenium is an essential trace element however, it is toxic if taken in excess at levels > 400-800mcg/d and can lead to selenosis
• Recommended Dietary Allowances (RDAs) for selenium is 55 μg/day
• major food sources of selenium in the American diet are breads, grains, meat, poultry, fish, and eggs.
• toxicity risk is mainly in China where people who ingest corn grown in extremely selenium-rich stony coal (carbonaceous shale which has selenium content of 9.1%)
• elsewhere, the most frequent ingestion resulting in acute selenium toxicity is that of gun bluing - children who ingest this suffer cardiovascular collapse within minutes of ingestion
• large amounts of brazil nuts has caused selenosis (each nut contains 68-91mcg)
• chronic toxicity may occur in taking selenium supplements
• selenium poisoning of water systems may result whenever new agricultural runoff courses through normally dry, undeveloped lands
• elemental selenium and most metallic selenides have relatively low toxicities because of their low bioavailability
• selenates and selenites are very toxic, having an oxidant mode of action similar to that of arsenic trioxide
  • chronic toxic dose of selenite for humans is about 2400-3000 micrograms of selenium per day
• selenium also occurs in organic compounds, such as dimethyl selenide, selenomethionine, selenocysteine and methylselenocysteine, all of which have high bioavailability and are toxic in large doses

• garlic odor on the breath
• metallic taste
• gastrointestinal disorders
• alopecia
• sloughing of nails
• fatigue
• irritability
• neurological damage - hyperreflexia, peripheral paresthesia, anesthesia and hemiplegia
• extreme cases may develop:
  • cirrhosis
  • acute pulmonary oedema (APO)
  • rapid cardiovascular collapse and death may occur in large acute poisonings
  • and may be fatal

• may occur in those with severe GIT malabsorption issues, on total parenteral nutrition, those aged over 90yrs and those dependent on foods grown in selenium poor soils
• it generally becomes symptomatic only when other stresses are concurrent such as mercury exposures or vitamin E deficiency
• it rarely occurs in absence of other issues hence effect of selenium deficiency on health remains uncertain