After exposure it will stay in the blood for about a month give or take, not 48 hours.
It is absorbed into the bone where it can reside for many many years, less for other organs. It is released back into the blood stream slowly so it will show up in blood work where you can asses your levels, no bone biopsy needed. I'm in the medical field...
Until 1973 or so pump gas had lead in it, although not good for humans we still survived. I don't use some of my equipment for many months, 100LL does not deteriorate or cause other problems associated with pump gas.
I'm not recommending it to anyone, but it serves a great purpose for me and will not have any adverse affects to my body in the way I use it.