Recently, I read something that said that you should never eat an onion (after it has been cut) except for on the day that you originally cut that onion. The author stated that onions have an "absorbing" quality that causes them to suck the bad things out of the air and into themselves. (He contends that they actually become toxic) And, he stated that, although they were fine when first cut, one should never "save" them for future use after they have been cut.
My apologies for this posting. I am somewhat embarrassed to even write it because it sounds so obviously incorrect.
But, I would very much like to know the answer since I am eating a lot of vegetables (of course). And, I am wondering if I have to waste an entire onion every time I want a few bits of one.