I'm having trouble finding references to support my claim, other than phytoplankton attaching themselves to plastic particles, which are then consumed by zooplankton, or plastic particles blocking sunlight thereby preventing photosynthesis, but nothing about actual plastic "consumption".

So if anything the plastic might be beneficial, assuming that it's able to decompose it and absorb only those atoms it actually needs as nutrients.

That's kind of what the person you are replying to is saying: if the plant is absorbing it, it's obviously been decomposed into its constituents and is actually beneficial to it.

It doesn't work the same as it does for an animal that eats in the standard way you use the word eat.

I was a bit confused (and at work) before but I was originally thinking of some species of dinoflagellates[0] who hunt/absorb/engulf prey (which I assumed to be larger than atoms), granted they are the exception. I could only find a study which noted higher concentrations of varying plankton/organisms (some dinofl.) near plastic[1] and partially related, on land some lifeforms were found to process PET bottles[2]. Life will hopefully find a way to process our trash before the ecosystem collapses ;)

[0]: http://oceandatacenter.ucsc.edu/PhytoGallery/dinos%20vs%20di...

[1]: https://www.sciencedirect.com/science/article/pii/S0025326X1...

[2]: https://phys.org/news/2016-03-newly-bacteria-plastic-bottles...