Strong winds blew some toxin across the dividing water to the other island. Testing was stopped, even to this day the island is still contaminated. Both biological and chemical weaponry are very sticky to use, produce, and control. Chemical weapons must be produced precisely, or else the weapon backfires and mutilates the builder. Industrialized countries frequently produce them with remote computer guided mechanisms to reduce the alarmingly high risk.
Biological weapons are even cheaper, and have an even greater effect.
The techniques are taught in undergraduate courses in Colleges and Universities worldwide. Only with BW do we need to consider how easy it is to possess, but how hard it is to control. The lifespan of many weapons is difficult to determine. Civilian populations also are decimated by biological warfare. The recent Ebola viral outbreak in Zaire shows how quickly infection spreads.