To take mercury for example, you can stick your hand in a vat of elemental mercury and be fine. A few drops of dimethylmercury on your skin can be fatal.
Sounds like a state actor's weapon of choice ...
A few drops on the outside of the latex gloves was enough to kill her. Maybe she would have survived if she'd changed the gloves immediately? Regardless, she didn't do that, and so didn't survive.
On Aug. 14, 1996, Karen Wetterhahn was exposed to dimethylmercury while making a standard for nuclear magnetic resonance studies related to DNA damage.
(...)
It was 5 full months before the consequences of that spill became apparent. Wetterhahn developed stomach problems, then began having trouble walking and speaking clearly. A friend, nurse Cathy Johnson, recalls a lunch date in early January 1997 when she urged Wetterhahn to see a doctor.
Within a few weeks, Wetterhahn was in a coma. On June 8, 1997, she died. She was 48 years old.
I always imagined all such nasty chemicals kill you in a matter of minutes to hours, days at the most. I never imagined they could turn you into a walking corpse. It's up there with Rabies.
But, luckily, I hit Google first. https://edis.ifas.ufl.edu/publication/FS437 showed that selenium does protect against mercury. Even dimethylmercury. And https://www.webmd.com/diet/health-benefits-brazil-nuts shows that Brazil nuts are an excellent way to get selenium. In fact it is comparable to a supplement, and a sustained diet of 3 nuts per day is already in the toxic range. I had no idea.
So it appears to be correct, there's a good chance that eating Brazil nuts could have saved her life!
(Was going to say it was "nuts" but abstained :)
May I ask why?
Depending on the compound, skipping this step may cause the compound to be relatively inert. This is why, for example, calcium carbonate is a poor source of calcium as a nutritional supplement, but calcium citrate is readily absorbed- the citrate itself is an organic compound, so the body more readily takes it up out of the digestive system and the calcium can be used.
Calcium carbonate will react with stomach acid to form calcium chloride (along with CO2 and water). When given intravenously, calcium chloride is perfectly bioavailable. However, within the small intestines, it has very poor uptake, both through the intestines' active and passive mechanisms. Any remaining calcium carbonate has no uptake at all.