In an October 2017 report, researchers from Harvard’s Belfer Center noted that minute quantities of anthrax
“equivalent to a few bottles of wine” could kill up to half the population of a densely populated city like Seoul.
North Korea could theoretically fire missiles with payloads of anthrax or other biological weapons into South Korea, or use drones to disperse the lethal substances from the air.
https://www.vox.com/world/2018/2/7/16974772/north-korea-war-trump-kim-nuclear-weapon