The general idea is to not ingest any heavy metals.
Well, that would be the safe route to kicking the bucket, since we need some of the "heavy metals":
Zinc is used in several enzymatic reactions in the human body.
Vitamin B-12 has a cobalt atom at its core.
Hemoglobin contains iron.
Likewise, copper, manganese, selenium, chromium, and molybdenum are all trace elements, which are important in the human diet.
Another subset of metals includes those used therapeutically in medicine; aluminum, bismuth, gold, gallium, lithium, and silver are all part of the medical armamentarium.
All in the correct amounts of course, or they may become poisonous.
We have no use for lead of course, but several factors make it a no/low concern in a hobby setting:
Soldering as a hobby, however strong a hobby, will never be comparable to what an industrial worker sees and for most, will never be a concern at all, fume extractors or not.
Personally, I have never used fume extractors or similar during more than four decades of hobby/pro soldering and quite often I hold the solder with my teeth/lips (not recommendable I guess) and not once during my regular monitorings - in several ways, including endless blood samples, scannings (X-ray/CAT/etc.) - they have found anything relating to lead.
I once (by mistake) got my mouth full of mercury. I spat it out of course, but some will allways enter your stomach in such an act.
Being a bit worried about it, I have talked to several doctors about it, but they have all told me that by ingestion of a heavy metal as mercury, it will pass through the system, since it is not able to "react" (or what the term is) in its metallic form.
When we get mercury poisoning, it is by eg. eating fish that has broken it down to forms that can "react" with our bodies.
I am not sure whether this counts for lead, but I comfort myself with the thought that lead is the closest thing to gold (only difference is one electron in the outer orbit of the atom), which is very non-reactive (although bad for your body in salts etc.)
If you start soldering nonstop for 8 hours a day, every day of the year, you should get protection like fume extraction and probably use something to hold the solder (whether containing lead or the alternative poisonous metals that comes with the unleaded variety) - just in case.
A minute amount of lead can transfer from fingers into your mouth if you solder and don't wash your hands before eating.
If anything, it will more likely be epidermis that takes it in.
Anyway, one should keep his/hers hands from the face unless there's a real need and allways wash hands before and after going to the face. For most people, bacteria and virii will be a far greater concern than lead. See a teenager with heavy acne and in 99% of the cases, it will be because he/she is having the fingers in contact with the face constantly.
Heavy metals accumulate in your body - I believe that they are not naturally evacuated.
If they are reacting, some of them (as mentioned, there are lots and some is needed) will accumulate in the soft tissue, but again, it's the salts and other variants that you are able to take in, not the metallic form.
Solder smoke can in theory carry fractional bits of lead - an atom here or there - but that precipitates out of the smoke inches away from your soldering effort.
You mean 'cause the lead atom is heavier than the fumes and the up-drift?
That's baloney. Any atom in the fumes will carry around throughout the room.
The solder smoke itself (burned flux/chemicals) has not been established as dangerous,
Oh well, as I've heard it throughout the last four decades, it is exactly the smoke that makes the fume extractions mandatory by law in a workplace in an industrial setting. Anything that smoke is potentially bad for your lungs, whatever's in the smoke.
The whole process of shifting to unleaded solder has to be seen in a globally optic and with an eye on the total lifetime of electronics devices; making, using and where it ends after use.
In that scale, lead free solder will probably be a benefit for the planet, if the alternatives won't be just as bad in other ways.
On a personal scale, however, I cant see it will do anything good or bad, except raise the temperatures of your soldering equipment (who said global warming
To cut a long story short... Chill out folks, you're likely to survive your hobby