First person to use lead as an additive ingredient of derv (6)
I believe the answer is:
leader
'use lead as an additive ingredient of derv' is the definition.
I can't judge whether this definition defines the answer.
'first person' is the wordplay.
'first' becomes 'lead' (lead can mean leading or primary).
'person' becomes 'er' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'lead'+'er'='LEADER'
'to' is the link.
Can you help me to learn more?
(Other definitions for leader that I've seen before include "Chief or front man" , "Head of an orchestra" , "Guide, commander" , "Director, guide" , "Front-runner or head of group" .)