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Estimation of lead contamination in 3D printed parts
Will lead from the nozzle make 3D printed parts non food safe?
Sometimes people talk about the presence of lead in brass nozzles of 3D printers and about the related "issue" of using 3D printed parts, contaminated with lead, in contact with food or beverages.
But is it really an issue? or is it something only people who didn't care or couldn't investigate the matter worry about? Do we need to use lead-free nozzles?
To most engineers, used to estimate stuff, such issue seems or should seem fishy, but I'll make now a very rough (and pessimistic) estimate to show how this fear is completely nonsense.
I assume we use non-abrasive filament, so plain PLA, PETG, ABS, ASA, ...
How much lead is in the brass of the nozzle, which is the only brass in contact with hot plastic? 3% at most in usual brass alloys, it is used to soften the material and to make it more easily machinable.
How much brass is getting removed from the nozzle and mixed with the plastic? judging by extremely, unrealistically worn out nozzles I have seen (which people usually won't reach) I would say no more than 2x2x2mm³, which means 64 mg of brass.
We talk about plain plastic, not abrasive, so it will take maybe 30 kg of filament to remove this amount.
How heavy is each printed part? Parts used for food-related applications are not huge typically, so let's say 0.1 kg which is unrealistically heavy. This means that 64 mg of brass are mixed with 300 printed parts, and each one will get around 200 ng of lead mixed in it.
It should already be obvious we are talking about a non-issue, but let's go on.
Unless the printed parts are pulverised and eaten or inhaled, they won't release all the brass (with lead in it) into the body. Only the surface of the printed part in contact with food or liquid will or may release material into them.
So, how much of the plastic will be affected by the contact with the food/liquids? Plastic is quite resistant to water and food in general at room temperature (we don't put printed parts in the oven anyway), so I would say, reasonably, only the surface in direct contact will release material. Assuming parts are all printed in double-wall (0.8 mm, which is rarely the case since we don't print pipes...), let's say 10% of the plastic (around the first 0.1 mm of thickness) is going to release brass with lead. So, out of the 200 ng of brass in the printed parts, only 20 ng of lead.
But the part won't release it all of a sudden, let's say over the course of a year? 3D printed parts I'm aware of last way more than that in water with less degradation, so releasing the 20 ng over a year is already a pessimistic estimate.
For hydroponics application there would be another step: how much of the lead released into the water is actually taken up by roots? they are quite good at selecting so surely not that much, but let's stick to 20 ng in a year.
It's 54 pg (picograms!) a day.
Now how much lead is allowed per day without (realistically) adverse effects? 5 μg per litre. If you drink 2 litres a day it's 10 μg of lead intake per day.
The 54 pg we calculated (pessimistic! in reality it will be way less) are 180 000 (180 THOUSAND) times LESS than what is allowed in drinking water.
Is it a problem? NOT EVEN BY FAR.
Someone may say that ehy, still pipes and other metallic parts in contact with food or water are required to be lead-free! Sure, but brass is considered "lead-free" when it contains 0.25% lead, for application in DIRECT contact with water. The nozzle is not, by far, in contact with the food, since only the printed part is, so 3% in the nozzle, which means hundreds times less than that in the plastic, is de facto the same as lead free.
No need to use steel or exotic materials for nozzles, just use plain leaded brass even for food-related prints.
The issue with food deposits and bacterial growth (even if usually overestimated) is more important than lead, which is NOT an issue at all.
Author: Olaf Marzocchi
First revision: 2023-08-04.
Last revision: 2023-08-04.