In 2005, the U.S. Environmental Protection Agency published a report, "Solders in Electronics: A Life-Cycle Assessment Summary," in which it "...assessed the environmental life-cycle impacts of selected lead-free solders as alternatives to tin-lead solder. The analysis also provides an assessment of the recyclability and leachability of the solders" (Ref. 2). The study considers leaded and lead-free solders from ore mining and waste recycling through refining and use to disposal and recycling again. Results show mostly small differences between the environmental impact of leaded and lead-free solders. After all, tin-copper, tin-silver-copper, and bismuth-tin-silver solders all require metal-ore mining and refining, fabrication, and disposal. And lead mining would continue because 80 percent of the metal still goes into vehicle batteries. I would bet less than one percent has gone into solders.
On his Signal Consulting Web site, signal-integrity expert Howard Johnson notes:
"Replacing tin-lead with pure tin is turning out to have been a huge mistake. There are two significant differences between lead-free assembly and lead-based assembly.
"1. Lead-free assembly is not better for the environment, it is worse. The additional tin mining required to produce high-purity tin alloys, plus the mining of other precious metals required to alloy with tin in substitution for lead is a poor trade for the use of existing lead, much of which comes from recycled products. This information comes from a study conducted by the U.S. Environmental Protection Agency (EPA). The study undercuts the primary basis for RoHS.
"2. Lead-free assembly is less reliable than lead-based assembly. The E.U. environmental commission admits this point. That's why they grant exceptions for military and high-reliability applications that still use SnPb solder. (Ref. 3)
Lead won't go into aerosol form or vapor form at soldering temperatures. The smoke is just flux, which is -much- more dangerous to breath.
And in fact, lead-free soldering requires a lot more flux, and the fluxes must be more aggressive. So the end result is likely to be more occupational hazards from lead-free soldering.