Rubbish duster, it is rotten (8)
I believe the answer is:
detritus
'rubbish' is the definition.
(I know that detritus is a type of rubbish)
'duster it is rotten' is the wordplay.
'is rotten' indicates anagramming the letters.
'duster'+'it'='dusterit'
'dusterit' is an anagram of 'DETRITUS'.
(Other definitions for detritus that I've seen before include "Accumulated debris" , "Refuse" , "Remains" , "Gravel or loose matter produced by erosion" , "Bits and pieces of rubbish" .)