tung oil is pretty toxic. boiled linseed oil has heavy metal salts in it to make it polymerize, though typically nowadays these are cobalt, iron, and manganese rather than lead; calcium and zinc are basically nontoxic alternatives
shellac is not water-soluble; it's alcohol-soluble and thermoplastic
the plantation sizes necessary to coat everyone's floor with tung oil or shellac are fairly modest
ionic cobalt and ionic zirconium are both of fairly moderate toxicity; they aren't in the same ballpark as things like lead and mercury, but they also aren't as relatively harmless as calcium or zinc
i think that normal 'boiled' linseed oil does have stand oil in it, as well as the siccatives we're talking about here and other additives like antiskinning agents
just to disambiguate, though, the risk of silica exposure from walking around on a concrete floor, or even sweeping it, is not worth worrying about. i wouldn't clean it with a leaf blower though
Shellac or traditional varnish are probably the only things you could put on your floor that aren't produced with an industrial process. Shellac in particular is the harvested secretions of a beetle that have been cleaned and dissolved in alcohol. But it's water-soluble and so probably not appropriate for use on a wood floor. You could also use tung oil or boiled linseed oil but you'd have to sand down to #0000 steel wool to get it to shine like urethane. Tung oil is a nice coating because it doesn't turn orange like BLO, but either one you will have to keep applying every few years or the floor will stop repelling water.
Obviously we'd end up with huge Tung plantations or Shellac plantations if we tried to replace all of our floor coverings with this stuff.