You can see a real-world of this in a very common building material, "wood". There's entire sub-ecosystems dedicated to breaking this material down... yet you c

You can see a real-world of this in a very common building material, "wood". There's entire sub-ecosystems dedicated to breaking this material down... yet you can safely use it to build structures that can stand for a long time, dozens or even hundreds of times longer than the breakdown time of the material in the wild, without the wood breaking down, as long as you maintain the structure, which mostly involves keeping the wood dry. These entire subecosystems for breaking down wood have fundamental chemical and energetic prerequisites in order to do their work, they are not just ambiently and actively roaming the Earth seeking out that which they may devour and actively creating the circumstances they can do it in. So I'm not worried about bacteria learning how to break plastic down in the middle of the ocean getting released into the grocery store one day and in mere hours the entire store is spoiled and destroyed. It would really just become another engineering consideration for materials that already have a lot of such considerations.