[aziaziazi]

They do: landfill are surrounded by fence and/or buried but most (not all) plastics degrades due to heat, sun, rain, ph of other materials and micro organism. Then all of those little flakes

- fly away with the wind

- are carried down the groundwater by rain. This is called leachate Modern landfills are protected by liners but those have a lifespan and eventually any of them could leak.