How are decomposers affected due to the usage of non biodegradable substances?

Hello Lepton, I'm no expert but I have covered this before. You just have to remember the 3 conditions needed for decomposition (heat, oxygen and moisture). Non biodegradable products must either have no fuel, or not much moisture inside them, the material could also be physically hard which means that decomposes will have a harder time breaking down the material.

Uh, that is incorrect. Decomposition can happen in the absence of oxygen (quite a bit of it actually) although it is typically slower than oxic degradation. Temperature is only so far relevant that it is not too low for biochemical reaction. Well, water is correct insofar as all living processes require water to some degree. The question in OP cannot be answered, however, as it simply does not describe sufficient parameters. What type of substances? How much? What system are we talking about?