I’ve use pla in salt water aquarium while it may dissolve over a long period of time it is insignificant the amount any chemicals that may leach into water also with proper tank maintenance via water changes this issue is greatly reduced.
PLA is a 3D printing material that is safe for food contact. With plastic injection molding, this material is used to make packaging. It is a perfect material to 3D print project that will not be exposed to the heat of to a too powerful mechanical constraint. But if you want to create litte objects with this biodegradable plastic, such as cookie cutters, PLA filament seems to be a perfect choice.