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...