If they used PLA(made of cornstarch) which is common for fdm 3d printing then theres no threat of microplastics from what ive read. it is biodegradable, but very slowly.
I doubt it's 100% cornsarch. I work in the plastics industry and there's all sorts of travesties going on. We also have a line of cornstarch-made products, but they're all scams when it comes to "recycling" and "being biodegradable".
From what I've read PLA is only biodegradable under very specific conditions. I looked into it and you have to send it to a recycling center designed for PLA and its expensive to do so. I would assume microplastics would still be present too. Even though it can be sourced from plant matter its still plastic.