How much lead is really on my hands when soldering?

Question

We have an electronic lab where we test and solder. There is a computer in the room as well. I have been wondering how much of that room is really contaminated with lead. We solder, go touch the oscilloscope or spectrum analyzer, google something here and there, open up all the drawers and what not etc. In my mind if were to visually see the lead in room I always think everything would be red. I rarely touch my phone while soldering or in the electronic lab but I've recently been doing so. When I follow what I touch when then going to the bathroom to wash my hands and then to my office, I think that lead is everywhere. I'm not talking crazy amounts just that it could be there. Sometimes I touch my keys etc. etc. etc.

So when one is dealing with lead solder, how much is really being transferred to other things when one touches their phone, a doorknob, the computer mouse/keyboard etc.? Or is it such a small amount that one shouldn't necessarily worry about it?

We use 60/40 solder.

Answer 1

This fear of lead is largely mis-guided. Yes, there have been reports of children falling ill from eating paint chips with lead in them. But this was made into a big deal because it happened to a child, whose quality of life suffered. But where are the reports of adults with lead-poisoning? Do any of those involve routes other than consuming lead? Why don't people whom are shot with lead bullets get lead poisoning?

The answer is the "consume-ability" of lead (and other metals) by the body. Half of the population has an amalgam of various metals (including mercury) in their mouths in the form of dental fillings. Mercury is extremely toxic; perhaps you've heard of the recent concern over mercury content of fish. Mercury doesn't seem to make anyone sick when it is in fillings however - but it does when eaten. And gold in fact, is even more toxic - but that is also a common tooth filling. However you can eat gold and it won't hurt you... what is going on here?

The process of eating metals is where the problem lies. In our stomachs lies very strong (hydrochloric) digestive acid. This acid breaks down most metals into a "metal salt" form, which IS absorb-able by the body. Once in the metal salt form, the trouble begins. Lead for example, is treated like calcium in the body, so it is stored in the bones.

Gold however, is not dissolve-able by hydrochloric acid, so remains inert.

There is a process to "rid" of the body of some metal contaminants, called chelation therapy. So if you know you have eaten lead, chelation will remove it from your bones. If it has been 20 years since you ate the lead however, the damage has already been done and chelation will help little.

So unless you've eaten lead, there really is no cause for concern. That said, you should be careful when eating after being near lead. Namely, wash your hands and avoid contaminating your food. Wipe down surfaces (do not use anything acidic) and consider them cleaned.

With toxic mercury in our mouths and deadly gold in our fillings, touching lead should now seem a lot less scary.

P.S. Note that modern solder is lead-free. So-called ROHS solder does not contain any lead at all. Still, eating it is a very bad idea so the same cleanliness guidelines apply. Standard 60/40 rosin-core solder is what this is referring to. Also note that acid-core lead solder, while rare today, may be potentially more hazardous due to the intrinsic acid content.

Answer 2

If you happen to be working with older equipment, or you are trying to exhaust a supply of old solder or old components, then there may indeed be a significant amount of lead in your environment. Note that I did not say a "dangerous" amount, nor did I say a "negligible" amount.

A common problem with older homes is that lead was also used in paint, so there are lead test kits on the market that you can use to look for lead in the environment. If you are worried, I suggest that you start with one of these.

Answer 3

Phones are everywhere, follow you home, and are difficult to wet clean so I keep mine in a PVC phone bag meant to be waterproof and I wash it down if it gets dirty with dish soap. Also helps when working around grease and gunk and stuff.

I've heard that people who cast bullets for long periods of time end up with visible, grey, lead residue on their hands. They are working with alloys of much higher lead content (>90%). Inkless pens also use lead (real Pb, not graphite) to make their marks but I don't know what alloy that is but that does give you an idea.

The Brinell hardness, which is indicative of how easily a material is rubbed off and leave residue, of the following materials is:

• 100% Pb is 5 BHN
• 63/37 solder is 17 BHN
• HB pencil lead is 14-15 BHN (obtained from bullet casters who use art/drafting pencils as gauges for the alloys they cast)
• F pencil lead is 16-18 (obtained from bullet casters who use art/drafting pencils as gauges for the alloys they cast)
• 6B pencil lead is supposed to be the same as pure lead, 5 BHN (obtained from bullet casters who use art/drafting pencils as gauges for the alloys they cast)
• softwood is 1.6 BHN
• hardwood is 2.6-7 BHN

And just for real world reference:

• Pure Cu is 35 BHN
• Pure Al is 15 BHN (the closest you probably see to this is aluminum foil)
• 6061 Al is 95 BHN (the kind you probably see if it is a chunk of aluminum)
• 6063 Al is 75 BHN (the other kind you probably see if it is a chunk of aluminum)
• mild steel is 120 BHN
• 18-8 stainless steel is 200 BHN (cutlery)

Plus larger particles produced from soldering which aren't as insidious because more difficult to spread

Buy a set of artist pencils and scribe them on some solder and find the pencil before and after it will no longer leave a mark on the solder. Then play around with those two pencils by lightly heading a piece of paper to get an idea of how easily the solder rubs off.