You will find lead, arsenic, cadmium, manganese and a host of other things you don't want to breath or ingest. These metals and additives are used to change the characteristics of the glass and to add color. When you solder, part of the lead and tin is vaporized into gas. Lead fume sticks to your hair, your clothes and your skin as well as our lungs. The more you get, the worse it is for you.
Children are particularly at risk from lead.
We all know the dangers of lead paint. Then there is flux. All fluxes are acids which allows the metals to bind. Which flux is the safest to buy, I don't know. I know it burns my eyes and smells to high heaven when I get downwind of my own soldering and I am using the newer cleaner water based flux.