Growth polluted a coastline (10)
I believe the answer is:
escalation
'growth' is the definition.
(I have seen 'Rapid growth' mean 'escalation' so perhaps 'growth' could also mean 'escalation')
'polluted a coastline' is the wordplay.
'polluted' indicates anagramming the letters.
'a'+'coastline'='acoastline'
'acoastline' is an anagram of 'ESCALATION'.
(Other definitions for escalation that I've seen before include "Rapid rise in level" , "sudden rise" , "Rapid growth" , "expansion" .)