Any evidence of real-world risk from someone else lead-soldering your devices?

Question

I appreciate this is likely neuroticism, but a luthier has recently worked on a couple of guitars of mine. He uses lead-based solder (entirely reasonably), but obviously that involves handling the guitar while soldering, and working on guitars in the same space as soldering generally.

Because I have a young kid, I would like for the risk to be nil. For other devices I'd just give everything a quick wipe down with lead removal wipes and call it good, but I suspect that would have an interesting effect on the finish of a guitar.

Most of the literature or questions I can find with regard to child safety relate to an ongoing source of lead - either someone soldering in the home, paint chips, pipes etc, which I suppose would make it a reasonable assumption that a contamination path of workbench/hands -> guitar -> my hands -> my keyboard/mouse/whatever -> child's hands -> child's mouth is pretty much negligble, but I don't like to assume when it comes to child safety! Kid occasionally plays with my guitars, but not often.

Is there any literature documenting the amount of lead dust/lead that's readily transferred from hands and surfaces to other surfaces relating to soldering?

Answer 1

According to Agency for Toxic Substances and Disease Registry of US Government,

Dermal exposure plays a role for exposure to organic lead among workers, but is not considered a significant pathway for the general population.

• Organic lead may be absorbed directly through the skin.
• Organic lead (tetraethyl lead) is more likely to be absorbed through the skin than inorganic lead.
• Dermal exposure is most likely among people who work with lead or materials that contain lead.

_{(my italicization)}

To clarify - Lead in solder is not organic lead, it's metallic lead.

The limit of for considering lead poisoning in children is 3.5µg/dL blood. With the density of elemental lead, that's one 42µm sphere of pure lead (that's a visible amount of lead) pr dL of blood. A child has 0.80-0.90dL/kg blood volume. Solder is not pure lead, but typically 30-40% by weight. So multiply volume by >2x-3x. Easily visible amounts of solder!

So, it's not healthy to chew solder joints - surprise surprise. As long as you're not getting acute lead poisoning, it's a question of decreasing the accumulated exposure during life.

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Regarding your suggested contamination path - There are two factors - probability of contamination from A to B, and the amount of lead that can be transferred. As a simple model - consider a compound interest type comparison - we assign some sort of probability to cross-contamination from each point to the next - that would be that probability to the power of 5. If you chose 50/50 as to get any lead from A to B - the probability would be a hair over 3%. Then you need to consider how much lead got transferred. It's easy to see that you're not able to transfer 100% of the lead during each probable transfer. That <100% transfer factor also compounds the same way.

Needless to say - of the very little lead that you were able to pick from the original exposure - very little is left, and it's unlikely to get all the way to the end of the chain.

It's impossible for someone here on an Electrical Engineering site to give you conclusive evidence to say there will never be 0% chance, 0% lead left, and in the end the risk evaluation will be completely your subjective decision. I would be more concerned about lead paint or eating too much tuna.

Answer 2

Officially, according to the (US) EPA, there is no identified minimum safe level for lead. Levels thought okay in the past have been revised downward.

EPA and the Centers for Disease Control and Prevention (CDC) agree that there is no known safe level of lead in a child's blood. Taking action to reduce these exposures can improve outcomes. Lead is harmful to health, especially for children.

So if you want the risk due to lead to be "nil", the exposure to lead should also be "nil".

Of course that's impossible, lead is an element and is present in some amount just about everywhere, and pursuing it would likely lead to unintended consequences that are worse than taking "reasonable" risks, but there you go.

Personally, I would have no great concern unless there was actual contact with the solder (especially mixed with eating acidic foods), or if solder paste was present. But my risk tolerance for my progeny may be different from yours.

Answer 3

According to the CDC, 20 to 70% of lead ingested into the body is absorbed, with children absorbing more. Lead can also be inhaled, although I don't think that would be the case for you. Unless if your child doesn't wash their hands, they should be fine. If the soldered connection is outside of the guitar, you might want to ask your luthier to use lead free solder as it doesn't cause lead poisoning. The downsides are that it is more expensive and it doesn't have joints as nice as leaded solder. But again, it is still better than lead poisoning.