Uncontaminated, set free over bug (7)
I believe the answer is:
sterile
'uncontaminated' is the definition.
(thesaurus)
'set free over bug' is the wordplay.
'free' is an anagram indicator.
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'bug' becomes 'rile' (both can mean annoy).
'set' is an anagram of 'ste'.
'ste'+'rile'='STERILE'
(Other definitions for sterile that I've seen before include "Incapable of reproducing" , "Not able to produce offspring" , "Non-productive" , "Not producing offspring" , "unable to reproduce results" .)