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Comment by DoingIsLearning | Hacker News Reader

I remember doing some consulting work for a medical device a couple of years back (embedded software) where they were really really struggling to design flexible tubing that would pass a bio-toxicity test.

In practice it seems plastic flexible tubing uses a lot of plasticizers (BPA included) to make them flexible.

My point being that, even if you avoid the packaging and the relabeled cosmetic 'perfumes', it still seems that the flexible tubing you would find in most coffee vending machines and water filtration systems (and many other consumer applications that do not require medical regulation) is probably choke-full of plasticizers.

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One of my first graduate tasks in a previous life involved managing the impact of switching to phthalate-free flexible tubing. We went nowhere near biological systems but were struggling to get hold of the stuff anyway.

It got to the point we were redesigning components to take into account vastly decreased maintenance intervals.

Whilst I don't want to defend the plastics industry, I have to find my delivery today funny: a small plastic part carrying a prop 65 warning. The part is made of polyacetal, and so contains no flourine, amine or cyano groups, no aromatics, not even a double bond.

How?!

Or even some household piping like PVC and PEX though with low exposure: “Phthalate exposure from drinking water via cPVC or PEX is low when compared to other dietary sources. Nonetheless, a shift from cPVC to PEX pipes in households would decrease potential exposure to phthalates.” [1]

1: https://hero.epa.gov/hero/index.cfm/reference/details/refere... with the full paper here https://ttu-ir.tdl.org/bitstream/handle/2346/87425/smith_art...

cpvc isn't that common in household pipes, is it? it's for sun exposure, i thought. Heat PEX has the lowest numbers.

Are there any pipes that don't leach anything into the water?

> cpvc isn't that common in household pipes, is it?

From what I have read it seems CPVC is used for residential hot water lines when copper is not being used (and copper is expensive).

I was assuming cPVC and PVC were the same but that is not the case. cPVC is more specialty when compared to PVC since it can handle a higher temperature and pressure, and costs a bit more [1].

1: https://pvcpipesupplies.com/cpvc-vs-pvc

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Some additional but not directly related info found along the way:

- https://www.cdc.gov/biomonitoring/Phthalates_FactSheet.html

- https://www.epa.gov/sites/default/files/2015-09/documents/ph...

For that to be true you would need chemically inert pipes, I can't really think of a material in common use that meets that specification. Opening the inquiry a bit to the less common materials:

Pure Soda Lime Glass

Synthetic Quartz

Diamond

Although these materials are poor choices for many reasons, they would be very unlikely to leach anything into the water more harmful than carbon or silicon atoms.

Don't most copper pipes get filed with a layer of limestone deposit? That basically acts like a calcium liner of sorts no?

This depends on local water hardness but generally is a stronger effect in hot water pipes because of the inverse temperature solubility of calcium carbonate.

Municipal water is definitely tuned to make a passivation layer on the pipe work.

you're not wrong that it would be preferable to have tubes that didn't need plasticizers, but generally water isn't going to sit in the tubing in a soda fountain or whatever for that long. Prolonged periods give a lot longer time for chemicals to leech, there is a "rate" component here, and the natural flow of liquid also means there is a larger volume of liquid involved, diluting things out.

which isn't to say that it isn't a problem either, but in relative terms here, what I'm saying is that water that sits in a plastic Nalgene bottle for a couple days probably is more concerning to me than water that passes through a few feet of plastic tubing inside a vending machine and never sits still for more than 10 or 15 minutes.

Although of course I suppose given the plastic tubes are more flexible than a hard plastic nalgene bottle, they may also have higher levels of plasticizers...

So maybe I'm showing how little I know here, but isn't these sorts of use cases exactly where you'd want to use silicone rubbers? Or do those have problems I'm not aware of? (other than being slightly spendy of course)

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