Disinfect chlorine seen to be sprayed over area (7)
I believe the answer is:
'disinfect' is the definition.
(I've seen this in another clue)
'chlorine seen to be sprayed over area' is the wordplay.
'chlorine' becomes 'Cl' (chemical symbol).
'to be sprayed' indicates an anagram (I've seen this in other clues).
'over' indicates putting letters inside.
'area' becomes 'a' (maths abbreviation).
'seen' with letters rearranged gives 'ense'.
'ense' placed around 'a' is 'eanse'.
(Other definitions for cleanse that I've seen before include "Make spotless", "Make thoroughly clean", "Free of sin", "absolve from sin", "give absolution".)