Plastic pollution isn't just a waste problem. It's a biological transport system. Here's what most coverage misses: plastics don't just float, they carry living organisms across ocean basins. A bottle lost in a UK river can end up in the Caribbean carrying bacteria, algae, or pathogens that evolved in completely different ecosystems. What's harmless in cold North Atlantic waters might be invasive or disease-carrying in tropical environments. This is called a transboundary issue, and it fundament