Hacker News Reader

Comment by _yb2s | Hacker News Reader

Plastic cutting boards are mostly just plain undyed polyethylene (HDPE)- which is just a fully saturated perfectly straight hydrocarbon, similar to saturated fat or wax and lacks the kind of reactive functional groups that make other plastic polymers toxic. I think it is quite unlikely that HDPE in particular is toxic or endocrine disrupting to humans in the way a lot of other plastics seem to be.

It's also basically just a very viscous fluid and I suspect would flow into grooves when a knife blade hits it, without releasing particles like harder more solid plastics would.

Personally, I try to avoid having most plastics contact my food and water, but make an exception for HDPE.

In general, each plastic polymer is very different from another chemically, and it makes sense to consider their safety independently, and not group all plastics together.

View on HN

Silicon dioxide is not chemically toxic. But you can put microfiber crystals of it in a mammal's lungs and get tumors that grow around them. It is not a huge stretch of the imagination from there to hypothesize that nano- and micro-particles of a nontoxic polymer could also cause problems.

True- I don't think they are likely to specifically exhibit the drug like toxicity that some other plastics are responsible for, but you are right that doesn't rule out other potential issues from a small, hydrophobic, physical object.

I'm not 100% sure HDPE is safe- and if not it might depend on how it is used, but I am less concerned about it than a lot of other plastics.

Since plastic vs wood cutting boards is what kicked this discussion off, I’d also point out fine wood particles will give you lung cancer too

The problem is cutting boards break off little bits of plastic with use and your body has evolved zero mechanism for disposing of microplastics once they are in your system.

https://www.ewg.org/news-insights/news/2023/10/making-meals-... https://phys.org/news/2024-12-microplastics-multiple-human-t...

I've looked a bit, and not been able to find evidence of HDPE getting into cells, or exhibiting biological toxicity, whereas there seems to be quite a bit of evidence of this for almost every other type of plastic. Still, I wouldn't blame someone for just avoiding all plastic food contact by the precautionary principle.

The first study you linked is interesting- it does seem to confirm what I suspected, that HDPE does flow on knife impact causing it to release less plastic debris than other plastics, but still not zero.

The second one seems to be a fairly low quality review article looking at what does sound like a concerning issue, but doesn't really consider different types of plastic independently. It might be useful in the sense of citing a lot of papers in this area that could be looked at directly.

That’s a good point. Why do they say water bottles are so bad? Can’t they use something like hdpe?

HDPE Nalgenes (branded "Ultralite") are my standard water bottle. Unlike the clear plastic sort, they're not see-through, nor very heat/impact resistant, but they weigh next to nothing. Just don't use 'em as a hot water bottle.

Same here, although they sadly discontinued the narrow mouth version.

The soft HDPE bottles are actually more heat and impact resistant than the rigid clear polycarbonate ones. They’re the standard recommendation for winter hiking.

https://momgoescamping.com/water-bottles-insulators-winter/

Honestly the water bottles are probably fine as they likely don’t leach much BPA unless something happens to break the polymer apart- like contact with a strong chemical solvent. Although BPA is an endocrine disruptor, it is likely that normal use of a polycarbonate water bottle is fine. They stopped selling them because people got afraid and stopped buying them. I still see no reason to use one given the uncertainty.

You can get really good HDPE, stainless steel, and glass water bottles with a silicon impact cover.

There's an argument that polycarbonate is very well-studied and the BPA released is low, while some of the alternatives have unknown risks.

> Plastic cutting boards are mostly just plain undyed polyethylene (HDPE)- which is just a fully saturated perfectly straight hydrocarbon, similar to saturated fat or wax and lacks the kind of reactive functional groups that make other plastic polymers toxic.

This is all just completely made up -- starting with the assertion that "plastic polymers" (whatever those are; you're not being specific enough to have a debatable claim) are "toxic" in the first place.

Everything I said are basic facts about plastic chemistry you can verify yourself, but I can elaborate more if that is helpful.

If you'd like a more specific example of what I am talking about, take for example Bisphenol A (BPA), one of the monomers used in making polycarbonate - which most people have heard of, and has now been eliminated from consumer products like water bottles (edited per correction from reply below). It is chemically similar enough to steroid hormones, that it can bind to steroid hormone receptors (in particular estrogen receptors), making it a potential endocrine disruptor. HDPE does not contain complex functional groups that are likely to mimic natural hormones and bind to receptors or enzyme active sites in a living system.

In general, molecules that contain a lot of aromatic rings, or reactive functional groups are more likely to exhibit drug like effects or toxicity. Such properties are systematically enriched for in chemical libraries used for drug discovery, but if trying to avoid unintended biological effects, it makes sense to exhibit more caution with such molecules.

> take for example Bisphenol A (BPA), one of the monomers used in making polycarbonate - which most people have heard of, and has now been almost universally eliminated from things that contact food and water for human consumption.

Why did they find large amounts of BPA in more than a few foods they tested if it has been eliminated from food manufacturing process?

Good point- what I said is wrong, it was removed from consumer goods like water bottles but is still legal and used in food manufacturing equipment in the USA. It has been banned in the EU from all food contact. I have edited my post above to correct this.

You should do as you want ofc but I don't trust anything that hasn't been proven toxic.

If they make a fine wine or a quality beer and put it in plastic (or something coated with plastic) I can't take the company seriously.

Tomatoes are the worse I hear because of their acidity. In the store there is a whole wall of canned tomatoes and plastic bottles. Non of the more expensive brands use it. The Tupperware comes out of the microwave all red? It even looks unappetizing.

If you can choose why go with the experiment? I'd pick the silverware over the plastic utensils every time.

My mum has been on the plastics thing since as long as I can remember (35+ years), we never had plastic in the house and if someone gave us something in tupperware mum wouldn't let us eat it, ha. Once I questioned her on this as I thought it was nuts, she said "plastic can melt, stretch, move, if it breaks off or leaks into our food it's toxic because it's chemicals, that is why we only use glass metal and wood in this house" - I still thought she was nuts, toxic plastic? What a load of hippie hogwash... I thought...

> Everything I said are basic facts about plastic chemistry you can verify yourself, but I can elaborate more if that is helpful.

Sure, go ahead. Nobody could verify what you claimed, because it was so vague to be undefined. That's the point.

You said something vague ("plastic polymers"), then you asserted toxicity (which is also a meaningless word -- nearly everything is toxic at some dose). As for the rest of the comment...I actually do have some training in chemistry and I have no idea what you're talking about. Just for example:

>> polyethylene (HDPE)- which is just a fully saturated perfectly straight hydrocarbon, similar to saturated fat or wax

No. Saturated fat is nothing like polyethylene. A fat is a triglyceride. A polyethylene molecule is not. You can't just wave your hands and say "they both have carbon chains" and draw broad conclusions from that.

Similarly, A "wax" can have all of the stuff that I think you'd (probably?) characterize as a "reactive functional group" -- things like esters, alcohols, and ketones.

> take for example Bisphenol A (BPA), one of the monomers used in making polycarbonate

You're trying to overgeneralize from very specific examples. Setting aside the evidence (or lack thereof) regarding the specific harm of BPA, the difference between BPA and even other kinds of polycarbonates is so vast as to be a meaningless comparison.

In biochemistry, the stereochemistry of a single bond can make orders of magnitude difference in toxicity, even if all the other atoms are the same. You can't just go "oh, it has rings/oxygens/whatever, so it must be toxic", or even "it looks like a fatty acid, so it must be safe".

I'm not writing a biochemistry textbook here (although I have done so)- the things you are saying are not new concepts to me. It is always challenging to be precisely correct, while clear enough to have a meaningful discussion with people of varying backgrounds.

Everything I said was very simplified, but could be much more specific with a lot more details that would be inappropriate for a HN comment- however I am happy to clarify exactly what I meant if you have more specific questions about what I mean. Indeed, each individual chemical structure can and should be evaluated for it's actual effects, and very small changes in structure can make a big difference. The importance of stereochemistry, and using biosynthesis to control it precisely is something I am very focused on. I stand by the claim that it is realistic to generalize that straight chain alkanes are well understood and have a lower risk of drug like effects than other classes of compounds, and mentioning fats and waxes here is an appropriate comparison in this specific context of risk assessment from limited evidence. Natural waxes - and most living things- actually do have a small fraction of saturated "fatty hydrocarbon" molecules that are not triglycerides/alcohols/etc. [1]. Some will even be unbranched alkanes, but with much much shorter chain lengths than HDPE. We also have liver enzymes that can convert these to alcohols.

I am an academic PI in this field, and much of my labs research is focused on discovery and biosynthesis of novel small molecule drugs, new plastic polymers predicted to have low toxicity, and saturated hydrocarbon biofuels. However, it is inappropriate for me to lay out a full technical description of exactly what I am thinking rather than a high level generalization in a HN post- for an audience that has largely never even had an organic chemistry course.

When I (or anyone else) is talking about the potential toxicity of plastic polymers, there are a lot of (hopefully) mutually accepted assumptions: we are talking about the real world exposure levels from real world regular use of products made from these. If I say "plastic polymers" in this context I'm talking about all of the common ones that are used in modern times to make things that contact food and water as a group- as done in the context of the article we are talking about. Doing so doesn't in any way conflict with the fact that this is a very heterogenous group with very different potential risks in different contexts.

Is it possible there is something else you are upset about here other than the specifics of what I actually said? There seems to be an undercurrent in your replies about being very skeptical of the idea that any of the widely used plastic polymers are possibly harmful, which I suspect is our real area of disagreement- and we would need to discuss the actual evidence of that for specific molecules with a lot more specifics to actually get anywhere. In a lot of cases the evidence is very minimal, and vague generalizations about the drug-likeness of monomer structures of the kind I am making here is the best current evidence one is going to have. One should absolutely be aware of how small changes in structure can massively alter toxicity, while still making generalizations with the evidence we do have about the relative probabilities of different biological effects from different broad categories of chemical structure.

We must make our decisions with the evidence that exists now, even if we don't like how little we have. One can and should collect better evidence to make better decisions as quickly as it is possible (to get funded to do so). If you're offering the funding, many people including me are quite prepared to collect better evidence starting immediately.

[1] https://www.sciencedirect.com/science/article/pii/S030881461...

As a chemical engineer who has worked in plastics manufacturing and has a degree in bioprocess engineering...The statements made by 'UniverseHacker seemed pretty reasonable.

The main point of contention for me is rather than establishing all HDPE as 'safe', it might be worth mentioning that some HDPE may have other chemicals added to it which could be harmful. Most HDPE doesn't have plasticizers like phtalates/etc added, but it's not completely unheard of. Some HDPE has been analyzed to contain ethylbenzene, xylenes, etc. And some HDPE is partially fluorinated.

https://www.pfasinsights.com/2024/01/u-s-epa-seeks-to-elimin...

Any thoughts on how to identify which HDPEs have those things as a regular consumer, without mass spec? I'd assume they add those to get specific properties for specific applications and knowing the application and/or that an expert could tell from simply looking at or feeling the material? This is stuff hard to figure out as an academic, because it seems to be mostly internal industry knowledge.

Reply on news.ycombinator.com