The most hazardous substance

For those who insist that plutonium is the most hazardous substance, and want to technically justify that belief, I estimate that it would take only about 10 grams of plutonium to kill everyone on earth assuming: all of the pu is converted to nitrate form, dissolved in water, and ingested by an individual. Death due to heavy metal poisoning will occur in a relatively short time. Following that individual's death, cremate the remains, extract the pu from the ash, and repeat the process 6 billion times. This may seem cumbersome, but then airborne distribution of plutonium in the form of respirable particulates has proven to be ineffective considering that since the time that several tons were so disbursed during the period of atmospheric nuclear testing, human life-expectancy has actually increased.

For those who believe iron is most is most hazardous, I have a scenario where it could be formed into a knife which could theoretically stab 6 billion people to death, etc..etc......