toxin, tocsin

Toxin or toxin means a harmful or dangerous substance; a poison--
The government is still trying to decide if the new additive should be considered a toxin.
Lead was removed from gasoline because it can be an environmental toxin.

Tocsin or tocsin ( rhymes with toxin ) means an alarm or siren, the kind you might hear on an ambulance--
They all ran at the sound of the tocsin.
The noise of the tocsin woke them up.

Now that you know that, you can say--
"They workers sounded the tocsin to warn the populace of a toxin escaping from the factory."

Note--"toxic" describes something poisonous--
Make sure the cabinet with the toxic chemicals in it is locked.