Noxious

[Hina Muqadas]

Hurtful; harmful; baneful; pernicious; injurious;
destructive; unwholesome; insalubrious; as, noxious air, food, or
climate; pernicious; corrupting to morals; as, noxious practices or
examples.

[Britney]

Harmful, poisonous, or very unpleasant.

[PussyCat]

Something, especially a gas or other substance, that is noxious is poisonous or very harmful: