Candidates flip on excavation emissions limits (8)
I believe the answer is:
nominees
'candidates' is the definition.
('nominee' can be a synonym of 'candidate')
'flip on excavation emissions limits' is the wordplay.
'flip' shows that the letters should be reversed in order.
'excavation' becomes 'mine' (mine is a kind of excavation).
'limits' means to remove the middle letters.
'emissions' with its centre taken out is 'es'.
'on' written backwards gives 'no'.
'no'+'mine'+'es'='NOMINEES'
(Other definitions for nominees that I've seen before include "runners" , "Candidates for election" , "Announced candidates" .)