Final answer:
Non-biodegradable plastics last for many years in landfill sites and pollute the ocean. Plastics that end up in landfills have slow decomposition rates and contribute to the long-term pollution of the environment.
Step-by-step explanation:
Non-biodegradable plastics last for many years in landfill sites. Many also pollute the ocean.
Most commonly-used polymers are not readily biodegradable, particularly under the anaerobic conditions of most landfills. What decomposition does occur will combine with rainwater to form leachates that can contaminate nearby streams and groundwater supplies. Partial photodecomposition, initiated by exposure to sunlight, is a more likely long-term fate for exposed plastics, resulting in tiny broken-up fragments. Many of these materials are less dense than seawater, and once they enter the oceans through coastal sewage outfalls or from marine vessel wastes, they tend to remain there indefinitely.
According to the information provided, plastic waste is filling landfills at a significant rate. Due to being non-biodegradable, plastic remains intact for many years, contributing to environmental pollution. Therefore, the missing word is landfill.