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"Poisonous" does not mean deadly. Some manifestations of toxicity are subtle. The dose, as always, determines if a plant is safe source of nutrients or a toxic hazard.

Selenium Metabolites

Certain Astragali act as accumulators of selenium. This is stored in the form of selenomethionine and selenocysteine (for the structure of these, see cys and met, replace the S with Se). Selenium is a required mineral for most animals. It acts in the form of a selenoprotein (which has Se-cys and Se-met residues) as an anti-oxidant. there is however a fairly narrow margin between sufficiency and excess. Toxicity tends to be chronic and result in alkali disease and blind staggers.

Excretion of Se occurs:

  • via urine in the form of trimethyl selenium, various selenates and the Se amino acids;
  • through the feces, in the form of Se amino acids;
  • through sweat in the form of selenates and di and trimethyl selenium
  • by respiration in the form of dimethyl selenium (giving the breath a garlicky odor)

When intake exceeds excretion for a long enough period of time, toxicity occurs.

Se tends to be transported from the gut to the liver via VLDL and LDL. Its highest tissue concentrations are found in the liver, red blood cells, spleen, heart, nails and tooth enamel, implying that during toxicity this is where most damage will occur. (Linder pg246, Casarett and Doull pg 658)

Selenium Poisoning
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