The last business crime fighters start exposing human destruction of the environment (7)
I believe the answer is:
ecocide
'human destruction of the environment' is the definition.
I can't judge whether this definition defines the answer.
'the last business crime fighters start exposing' is the wordplay.
'last' says to take the final letters.
'business' becomes 'co' (short for company).
'crime fighters' becomes 'cid' (I am not sure about this - if you are sure you should believe this answer much more).
'start' suggests taking the first letters.
The last letter of 'the' is 'e'.
The first letter of 'exposing' is 'e'.
'e'+'co'+'cid'+'e'='ECOCIDE'
Can you help me to learn more?
(Other definitions for ecocide that I've seen before include "Deliberate destruction of the environment" , "Environmental ruin" , "Destruction of the natural environment" .)