Your food should be grown without the aid of chemical fertilizers and should contain no residues of toxic insecticides, chemical additives or preservatives.
Almost all food sold at supermarkets today contains some chemicals, either used in food producing or added during food processing or packing. Many of the poisons in fruits or vegetables are systemic, that is, they cannot be washed out or peeled out, as they penetrate the whole fruit. The only solution seems to be to grow your own food, or buy the certified organically grown food. And, of course, to avoid eating all processed and packaged foods, which contain the most chemicals.
Since it is unlikely that in this poisoned world any of us can escape getting some poisons into our systems, it would be wise to know what are the common poisonous elements in our environment and also to know how to protect ourselves against these poisons from our food, air, water and environment.