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Comment by culi | Hacker News Reader

Just so anyone doesn't get the wrong idea, this is about a specific algae-based polymer being developed by UCSD.

> Microplastics can take anywhere from 100 to 1,000 years to break down and, in the meantime, our planet and bodies are becoming more polluted with these materials every day

In general "biodegradable plastics" currently on the market should still be heavily scrutinized. So far it mostly has just meant it gets to the microplastics stage faster than other plastics. Not only does this have negative health consequences for us and fish, but it also makes it much more difficult to ever recycle and re-use these plastics

https://www.biopak.com/au/resources/biodegradable-plastic-pr...

Still, it's exciting to see progress on the possibility of an actually sustainable version of biodegradable plastic. Hopefully it can scale and doesn't lead to other micro pollutants

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>Not only does this have negative health consequences for us and fish, but it also makes it much more difficult to ever recycle and re-use these plastics

Are there any actual concerns with pure PLA?

"Environments without the necessary conditions will see very slow decomposition akin to that of non-bioplastics, not fully decomposing for hundreds or thousands of years.[59]"

https://en.wikipedia.org/wiki/Polylactic_acid#Degradation

No mention of its actual life cycle as it turns into a microplastic ie so it should be presumed dangerous in the same ways.

As a microplastic absorbed by organisms, it is quickly absorbed. But idk of what absorption means to the absorbing organism, hopefully we have some data on that. Absorbed might not be the same as harmlessly absorbed and metabolized.

I suspect they are referring specifically to PLA.

PLA pretty much just breaks down into microplastics unless it's decomposed in an industrial composting facility.

There's no such thing as pure PLA, like all industrial plastics it's filled with additives to improve its properties and these have endocrine disrupting / carcinogenic properties just like all the others.

Endocrine disrupting plasticizers are not used in all plastics, and they’re not used in basic PLA.

You really cant generalize “all industrial plastics” as “plastic” is way too broad a concept. Good engineering plastics like PEI/PEEK dont even need to use any additives like plasticizers, stabilizers, cross linkers etc.

PLA etc are just fine, they might not biodegrade quickly outside of a compost pile, but they are not making indefinitely persistent microplastics. Indeed, medical implants made of PLA are reabsorbed in mammals. The same cannot be said of PETE fibers accumulating in various tissues.

Just a note, PLA is industrially compostable, but it won't biodegrade quickly if at all in your backyard compost pile

It will biodegrade just laying around anywhere, with not even a backyard composter, 1000x sooner than all the normal plastics.

Some other things can even go faster and easier, but you can use pla without feeling guilty of anything.

It doesn't do the world any good to make anyone wary of such a huge improvement.

1000x sooner is still a really long time, I've seen numbers like 80 years thrown around. And that's with normal PLA, not PLA+ and other popular modifications that may have very different properties. You are right that it's significantly better than ABS for example, but "less environmentally hostile" and "environmentally friendly" are not the same and imho a lot of the info out there is simply misleading in that regard.

It doesn't do the world any good to lie about the degree to which things help either! We can be realistic about our need to properly dispose of PLA in an industrial composter, and still accept that it's a massive improvement over other plastics

> PLA etc are just fine

Define "just fine". PLA microplastics can have strongly hormonal effects. In european perch, for example, they were even found to significantly alter social behavior.[0] MPs can cause tissue damage, oxidative stress, and changes in immune-related gene expression as well as antioxidant status in fish[1] and humans may experience oxidative stress, cytotoxicity, neurotoxicity, immune system disruption, and transfer of MPs to other tissues after being exposed to them.[1][2]

[0] https://www.sciencedirect.com/science/article/pii/S004896972...

[1] https://www.frontiersin.org/articles/10.3389/fenvs.2022.8272...

[2] https://www.undp.org/kosovo/blog/microplastics-human-health-...

When they say break down they just mean even more micro than microplastics right? It’s not truly breaking down right?

Nope, truly breaking down and digested by bacteria.

> The last measurement involved chemical analysis via gas chromatography/mass spectrometry (GCMS), which detected the presence of the monomers used to make the plastic, indicating that the polymer was being broken to its starting plant materials. Scanning-electron microscopy further showed how microorganisms colonize the biodegradable microplastics during composting.

No I mean regular plastics. They’re not truly going to get broken down in a 100 years, they’re just going to be really tiny.

Regular plastics are truly broken down over the long term by environmental bacteria.

"Degradation and metabolism of synthetic plastics and associated products by Pseudomonas sp.: capabilities and challenges"

https://enviromicro-journals.onlinelibrary.wiley.com/doi/pdf...

Long-term exposure to sunlight and physical abrasion contributes to the formation of microplastics (<5 mm). Microplastics can be degraded further by microorganisms. Consequently, biological degradation and subsequent metabolism have the potential to eliminate plastics from contaminated environments.

...

With respect to plastic degradation, the species of the genus Pseudomonas are amongst the most cited degraders of various extents for a wide range of plastic polymers. Complete biologically mediated elimination of plastic polymers first requires breakdown of the polymer into smaller oligomers and, eventually, monomers that can pass through the cell membrane followed by assimilation and subsequent intracellular metabolism. Here, we present a review of the capabilities of species of the genus Pseudomonas to degrade and metabolize synthetic plastics.

If you like set it on fire it decomposes into gas to the point they're not the same compound, they don't come back down into micro-particle slug of same thing like gaseous gold would, and there is always that bacteria known to scientists that can break down certain kind of plastics in that manner for almost all common plastics

I interpret "disappear" to mean "dissolve completely". Not so ?

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