Fruit growers often spray their fruits with insecticides and fungicides designed to prevent the action of insects, fungi and other microorganisms that could devalue their crops. These substances are generally produced from copper sulphate, the effects of which are shown to be sufficiently safe. That is why various fruits - grapes, figs, etc. - often they are sprinkled with blue or green. They are dry residues of sulphate.
This substance protects the fruit, but is poisonous, and even dangerous, for the human organism. A scientist, who has done a meticulous study of the maturation of fruits, announces that in his opinion these foods can be dangerous when ingested without being washed, because fruit growers often spray fruit with poisonous substances, to kill insects and worms, being part of that substance impregnated in the shell. This scientist has verified serious diseases resulting from these poisons, so he warns all fruit consumers to wash them carefully in order to rid them of poisonous substances.
The care of removing any residue of toxic substances from the surface of the fruit, logically fits the consumer. So it is never too much to insist repeatedly that the fruits be washed one by one. It is not enough to let water run over them; you need to wipe them slightly. And this in any case, even if there is no sign of the presence of any sulfate residue and its companions. It's that they can be hidden in spots that are barely visible. In many cases washing the fruits is not enough; it is necessary to peel them.