Humans throw-away tonnes of plastic every day without even thinking that the same plastic is returning to them and can affect their biological systems. The plastic we throw away every day affects the entire ecosystem. Recently, a plastic dump was found stuck in the Arctic ice. When the plastic we throw away ends up in the water, tiny organisms ingest them and it enters their biological system as another eats on them and the cycle continues.
This is what biologists call bio-magnification. When organisms were exposed to plastic, it was seen that the plastic affected their biological system. For instance, when a team of scientists at the University of Plymouth exposed marine mussels to microplastics, they saw these microplastic damaged their DNA, ruptured their digestive tracts and deformed their gills. The same applies to other organisms as well. The plastic we throw aways turns into microplastic and nano plastics, which are so tiny and destroy biological systems. These nano plastics and microplastics are so tiny that they are indistinguishable from crustaceans, birds and other organisms.
Not only water, lots of microplastics and nanoplastics also end up in the soil which later gets incorporated by the bacteria, fungi and detritus living in the soil, therefore, screwing up the food web of the soil. The microbes in the soil have a special role in decomposition and affecting them would result in a disturbance in the process of decomposition. There are numerous studies done on how these microplastics and nanoplastics are degrading the ecosystem.
An interesting fact is that humans are the only species who are using plastic in day to day lives if we adopt some better choices or alternatives, we can save the whole ecosystem.