Cordon off contaminated soil with a hollow tube (7)
I believe the answer is:
isolate
'cordon off' is the definition.
(thesaurus)
'contaminated soil with a hollow tube' is the wordplay.
'contaminated' is an anagram indicator (a corrupted spelling).
'with' says to put letters next to each other.
'hollow' says to hollow out the word (remove centre letters) (the word is hollowed out).
'tube' with its centre taken out is 'te'.
'soil' anagrammed gives 'isol'.
'isol'+'a'+'te'='ISOLATE'
(Other definitions for isolate that I've seen before include "Set apart from others" , "Set apart, quarantine" , "Place apart from others or alone" , "Place or set apart" , "Seclude" .)