> Even if the retailer took it back it would still be... trash.
Yes, but making them deal with it would create a massive incentive to either reduce the amount of rubbish they make, or to make it recyclable/processable.
It's an externality because the entity that sold it to you doesn't have to pay the consequences of dealing with the trash. OP said "dispose of it properly," which could mean a lot of things, all of which are better than leaving it on a beach.
Trash disposal (to regulated landfills, not beaches) is enormously inexpensive and increasing the cost of every item through a laborious return program doesn't improve anything.
> Nearly all the plastic humans have made still exists.
And it just doesn't matter. It's a tiny amount of mass / volume.
> The great garbage patch in the Pacific is growing fast.
Ocean plastics are almost entirely a consequence of (particularly Indonesian) fishing net waste, not Western consumer products disposed of in managed landfills. The "great garbage patch" is also very much overstating the scale of the problem; it's a slightly higher plastic density region of ocean.
The main thing about plastic is that it’s made from oil, and oil already exists in the ground. Putting it back into the ground is basically neutral minus the pollution involved in manufacturing.
Geological strata vs shallow landfill sitting above aquifers and subject to near-term erosion.
Disposing of this stuff in deep mines seems like it'd be fine, unfortunately we haven't yet, at a society/economy level, found the discipline to do so. Presumably after a few mya of heat and pressure it'll be indistinguishable from other petrochemicals (which aren't particularly nice to begin with).
I don't think disposing of stuff deep in mines would be a good idea as it would be easy to contaminate the ground water. Modern landfills are generally well engineered and don't contaminate the surroundings too badly.
It doesn't go "back in the ground" though, does it? It gets scattered all over the ecology. When you take something that was buried deep and scatter it all over the surface - especially when that something is oil - that's usually considered an ecological disaster. Deepwater Horizon, the worst oil spill in history, has had catastrophic effects on the local wildlife, and it is still dwarfed in scale by the amount of plastic annually strewn to the four corners of the Earth.
7 billion kg at the density of water would fit in a cube 200 m on each side.
All the plastic ever produced could be stuffed back into one medium size coal mine. There are thousands of such mines and they are already ecologically disruptive.
It's a large amount when you think about the logistics to move it around the world, but a small amount compared to the total amount of stuff we take out of the earth.
As mentioned in the other thread, ocean plastics have nothing to do with landfill-disposed trash. They're mostly fishing nets waste, and at that, mostly from mismanagement by a handful of poor countries.
I'll assume good faith here and that you were simply unaware of the origins of the so-called great garbage patch, but in future discussions I think it would do your arguments some credence not to bring up ocean plastics in response to discussion about landfills.
