I would think resin is biodegradable. Off course there are many sorts or resin. What if we use a natural one?
The other factor is how harmful the object is per se, example:
- a bar of mild steel
rusting on the shore is not considered harmful,
- a bar of lead is,
Etc., I might be wrong in my examples (I was poor at chemistry once) but I hope you are getting my drift.
Another example can be 'solar energy is green' - OK - how green is the process of manufacturing a solar
panel ... ??? (Tip - it is NOT).