Take a look at these links:
What you should remember when handling Selenium, is that it is a non-soluble, rare Earth mineral. It should be handled only with protection: wear gloves, protective eye gear, and in a well-ventilated area.
Toxicity: At high doses (> 900 µg/day), selenium produces a toxic syndrome consisting of dermatitis, loose hair, diseased nails, and peripheral neuropathy associated with plasma levels > 100 µg/dL (> 12.7 µmol/L).
I hope this helps.