Toxicity and environment
Metallurgy of selenium and tellurium

Being strong reducing agents, selenium and tellurium have a marked effect on living organisms. In their solid state, these elements are practically harmless. On the other hand, selenium vapours and its hydride are highly toxic [39] . The toxicity of the hydride, which boils at 42°C, is very marked. The same applies to halides and oxides, which are also powerful reducing agents. Soluble selenites and selenates, and organoselenates must be handled with care [23] .

Like selenium, tellurium poses toxicity problems through its hydride (whose very unpleasant odor is perceptible...