most deadly toxin in the world
Either way--don't play with plutonium. The most toxic substance I could come up with is botulinum toxin--yes, the same material that is purified and injected (Botox) to remove wrinkles! When injected, the fatal dose is 1.3 to 2.1 nanograms per kilogram. So for an 80 kg adult, 104 to 168 nanograms (0.000168 mg).