America turned dirty on a continuing basis (9)
I believe the answer is:
sustained
'on a continuing basis' is the definition.
(as in a sustained or continued action)
'america turned dirty' is the wordplay.
'america' becomes 'US' (United States).
'turned' is a reversal indicator.
'dirty' becomes 'stained' (made dirty by a stain).
'us' written backwards gives 'su'.
'su'+'stained'='SUSTAINED'
(Other definitions for sustained that I've seen before include "Kept (something) going" , "held up" , "Long drawn-out" , "Steady" , "prolonged" .)