Selenium toxicity

Selenium is probably the most toxic, weight for weight, of the essential nutrients. Very few instances of human selenium intoxication have been recorded.

Selenosis, a condition defined by blood selenium levels greater that 100 ug/dL, can result in symptoms including gastrointestinal upsets, hair loss, white blotchy, nail brittleness, garlic breath odor, fatique, irritability and mild nerve damage.

Acute poisoning of selenium is lethal, with damage occurring to most organ system. It produces central nervous system effects, such as nervousness, drowsiness and convulsions.

It has been observed both in miners and in people who consume excess selenium form supplements. 

Manifestations of selenium toxicity depend on dose and duration of exposure, on route of exposure and on the chemical form of selenium.

The most toxic forms of selenium are sodium, selenite, sodium selenate, selenomethionine, and selenodiglutathione.
Selenium toxicity