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Comment by powerbroker | Hacker News Reader

I understand that the pits, that are the foundation of landfills, are lined with impermeable plastic sheets. Their purpose is to avoid ground-water contamination. So, there may be some redesign of landfills required before this technology can succeed.

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There are many different types of plastic and they have surprisingly different molecular structures. Enzymes are remarkably specific catalysts, so an enzyme that eats PET [1] can’t eat another type of plastic, like HDPE [2]. So one solution could be to engineer an enzyme that can’t eat the liner material.

I’m not sure if HDPE would make a good liner material or not, but just as an example, the differences in molecular structure between PET and other plastics are big enough that it would take an array of different enzymes to eat them all.

1. https://en.m.wikipedia.org/wiki/Polyethylene_terephthalate 2. https://en.m.wikipedia.org/wiki/Polyethylene

I was thinking the same. Worst case scenario with a solution like this one is that these organisms get into the wild, gain more mutations, and then rapidly release a large volume of carbon, currently sequestered as plastic, into the atmosphere. Or, plastic-tropic organisms used as a weapon, sprayed over cities, etc.

Perhaps plastic should start being compressed into bricks for long term storage that does not lead to leaching.

Note: the article talks about an enzyme, which is a simple protein. They might manufacture it via organic means, but the enzyme by itself has no capacity to reproduce or mutate.

That is true, but the best and easiest way to make a huge mass of a specific enzyme is to grow it in something, either bacteria or yeast. If it is in an organism, the organism can escape into the wild.

That's a much smaller threat than if the organism itself were to be applied directly to plastics.

Designer organisms aren't generally well-suited to spreading in the wild and even if they were, they could be engineered to require a certain dependency that they would die without. But yes, still theoretically it's possible.

Did I miss something? What organism are you referring to?

An enzyme is a protein not an organism

An enzyme is a protein molecule, not a living thing. Probably the biggest risk is that some wildlife or fish may be allergic to it.

I thought it's usually just natural clay, but I bet it varies based on local conditions.

According to this, a municipal landfill in the US requires:

> a flexible membrane (i.e., geo-membrane) overlaying two feet of compacted clay soil lining the bottom and sides of the landfill.

https://www.epa.gov/landfills/municipal-solid-waste-landfill...

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