Burying plastics results in leaching phthalates, estrogen mimics and assorted other crap into the ground, and groundwater, in the near term, not the far future.
https://www.urologytimes.com/view/testosterone-levels-show-s...
Now of course an average 3rd world country doesn't have any of that, but if you would actually travel there you would see plastics everywhere, in the sea, on random land, in the mountains, in the rivers etc. While still leaking what you wrote but way more directly.
> Modern landfills are completely sealed to reduce contamination of the nearby groundwater. First, the ground is lined with clay. A thin layer of flexible plastic is placed on top of the clay layer. That allows the collection of leachate, the liquid that passes through the landfill and may draw out toxins from the trash. The leachate is collected though a drainage system that passes this contaminated water through pipes to a pool where it can be treated to remove the toxins before being released back into the environment.
https://education.nationalgeographic.org/resource/landfills/...