Region died: toxin released poisonous gas (8,7)

I believe the answer is:

nitrogen dioxide

'poisonous gas' is the definition.

'region died toxin released' is the wordplay.
'released' indicates anagramming the letters (letters released from their original order).
'region'+'died'+'toxin'='regiondiedtoxin'
'regiondiedtoxin' is an anagram of 'NITROGEN DIOXIDE'.

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app