Soil thrown in trash (7)
I believe the answer is:
tarnish
'soil' is the definition.
(thesaurus)
'thrown in trash' is the wordplay.
'thrown' is an anagram indicator.
'in'+'trash'='intrash'
'intrash' with letters rearranged gives 'TARNISH'.
(Other definitions for tarnish that I've seen before include "Discolouration of metal surface" , "Discolour - sully" , "Lose lustre; sully" , "spot" , "Take the shine off" .)