If anyone really cares about how many bananas it takes to kill someone, here is a site where they have looked into the absurdity.
http://quarksandcoffee.com/index.php/2015/10/08/how-many-bananas-does-it-take-to-kill-someone/ The 200 bananas in the original post is supported by the calculation in the third paragraph which is slightly less but close. Spoiler: it is not the radiation per se that is toxic so much as the salt of potassium KCl and the fact that its toxicity in large doses is due to the chlorine, in addition to radioactivity. “Bananas contain a relativity high dose of potassium in the form of a salt called potassium chloride (KCl). While potassium is essential to healthy humans [5], anything can be bad or even dangerous in large enough doses. The daily recommended value is thought to be between 1600 to 2000 mg, and bananas contain about 1/4th of that with 451 mg [6]. So what if you got too much potassium? In toxicology, the LD-50 is a metric that used to describe a lethal dose of a chemical in 50% of cases. Equivalently, if exposed to an amount equal to the LD-50 you’d have a 50% chance of dying. I couldn’t find the LD-50 for KCl in humans, but it’s been found to be 2600 mg/kilogram (of body mass) in rats [7]. Assuming it’s the same for humans, the LD50 for an ordinary mass human (65 kg, 143 lbs) is 169 grams (0.37 lbs). Since the K is responsible for 52% of the mass of KCl, and since a banana contains 451 mg of K, it means a banana contains a total of 867 mg of KCl. Thus, a person would have to eat 195 bananas to get a lethal dose of KCl. Don’t worry if you’ve eaten 194 in your lifetime. Your next one won’t kill you, you’d have to eat all 195 bananas in a sitting. Also, this is not a good way to die. Potassium overdoses induce a condition called hyperkalemia, which can seriously mess up your heart. For this reason, large doses of KCl are actually administered as a part of the lethal injection.”
