Snap over final talk about cause of environmental damage (7,3)
I believe the answer is:
'cause of environmental damage' is the definition.
(plastic bags are bad for the environment)
'snap over final talk' is the wordplay.
'snap' becomes 'pic' (short for picture).
'over' is an insertion indicator.
'final' becomes 'last' (synonyms).
'talk' becomes 'bag' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'pic' placed around 'last' is 'plastic'.
'about' is the link.
(Other definitions for plastic bag that I've seen before include "Supermarket shopper" , "Shopping carrier?" .)