Degrades arsenic by injecting root (6)
I believe the answer is:
abases
'degrades' is the definition.
(I've seen this before)
'arsenic by injecting root' is the wordplay.
'arsenic by' becomes 'as' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'injecting' is an insertion indicator.
'root' becomes 'base' (synonyms).
'as' going around 'base' is 'ABASES'.
Can you help me to learn more?
(Other definitions for abases that I've seen before include "humbles" , "Takes down" , "Humiliates, belittles" , "degrades" .)