When plant-derived plastics are decomposed in ammonia water, they are converted into urea and monomers. Since the monomer is also plant-based, it is not harmful even if it is spread on fields. The monomer can also be reused to make plastic (Source: Japan Science and Technology Agency).
Plastic, once a nuisance, can now be used as fertilizer! What is the earth-friendly plastic developed by a research team of Chiba University and others?