Peru turned out to be uncontaminated (4)
I believe the answer is:
pure
'to be uncontaminated' is the definition.
('pure' can be similar in meaning to 'uncontaminated')
'peru turned' is the wordplay.
'turned' is an anagram indicator.
'peru' with letters rearranged gives 'PURE'.
'out' acts as a link.
(Other definitions for pure that I've seen before include "free of contaminants" , "free of bad grammar" , "Untainted" , "Virgin" , "Chaste" .)