At university, arsenic is found -- a poisonous substance (4)
I believe the answer is:
upas
'a poisonous substance' is the definition.
(tree with poisonous sap)
'at university arsenic' is the wordplay.
'at university' becomes 'up' (slang term meaning at university).
'arsenic' becomes 'As' (As is the chemical symbol for arsenic).
'up'+'as'='UPAS'
'is found' is the link.
(Other definitions for upas that I've seen before include "Tree from Java with poisonous sap" , "A poisoner" , "Sap used to poison arrows" , "Poisonous Javanese tree" , "Java tree providing arrow poison" .)