Why would a bottle of water last “forever” in a landfill?
I know its not a naturally occuring substance, but it is made of natural molecules, atoms, etc. Why won’t it break down naturally?
Because if you’re deep enough in a landfill, it will not be exposed to the oxygen-rich environment that contains the organisms that will break it down quickly. So while perhaps not “forever”, it would probably last tens of thousands of years absent active insertion of materials/organisms to break it down, or the relocation to a more suitable environment by natural or manmade processes.
They don’t mean “forever” literally. They mean “a very very long time - certainly longer than you’d WANT it to be in a landfill”.
Things break down either by getting devoured by living things or by mechanical/chemical erosion like wind or acid. Plastic is pretty durable against both of those approaches. Bacteria and worms don’t eat it, the wind doesn’t get to it, and the heat/pressure in a landfill isn’t that great.
I’m not sure about that, normally the things I send to a landfill, I have no desire to ever see again.
Sense the primary components of plastic water bottles are petroleum based, bacteria and worms don’t eat oil either, seems like since the oil came from the ground the logical place for its reincarnation would be back in the ground.
that didn’t work well in cases like Love Canal.
Petroleum comes from below aquifers that source much our drinking water. Landfills are above the aquifers and if they aren’t sealed and never leak they will potentially contaminate that water.
Why should I *object *to it being in a landfill?
I’d object to it being dumped at sea, for instance, where it might join a floating trash island, and affect the marine life. But properly disposed of, and then buried underground, out of harms way, what exactly is the problem with that?
You’re (completely) missing the point. It’s a catchy little phrase, meant to encourage people to a) stop buying so much damned bottled water or b) at the very least recycle that empty bottle. Stop taking things so literally - not everything is a PhD thesis requiring rigorous scrutiny and criticism.
Plastics don’t break down because they don’t corrode and nothing living has yet evolved the ability to break them down and eat them.
This is a good thing in the case of sewer pipes (made of PVC or HDPE) and landfill liners (made of HDPE). We expect sewer pipes and landfill liners to last at least 100 years, and they will likely last longer than this.
This is a bad thing in the case of expecting the plastic to break down naturally. Interestingly, nothing much breaks down in a landfill due to the absence of oxygen. All you get is the very slow anaerobic digestion of organic matter (primarily food waste), resulting in the evolution of methane gas from the landfill. Everything else is pretty much sealed in a time capsule, like newspapers. About 3 years ago, I personally picked up a newspaper sheet out of an excavation (a full sheet from the New York Sun that was dated October 1940) that still looked new.
What does tend to break down plastics is exposure to oxidizers such as UV light (like sunlight).
Because landfills fill up. Once the bottle is in the landfill it will stay there indefinitely, along with all the bottles that get pitched in after yours.
An hour on a treadmill?
Holy sh!t, no wonder I’m still fat. I thought it was 20-30 minutes 3-4 times a week?
In addition, to avoid leaching, the plastic in water bottles is exceptionally stable, and so breaks down even more slowly than usual.
Now how long the treadmill lasts in the landfill is another matter.
Not so fast… life will find a way 
Though there are only a small handful of bacteria that can “eat plastic”. This one in particular eats nylon byproducts and evolved in waste ponds of nylon factories. And some others have been engineered to digest other kinds of plastic.
We need to site our landfills on subduction zones so they’ll be sucked down into the mantle every few hundred thousand years. That’ll keep up with the garbage mountains we produce every year.
Yeah, right …
You’ve been reading David Brin!
Here in Minneapolis, all our non-recycled garbage is burned and turned into energy. They love plastic bottles like this; they are an oil byproduct, and burn very well.
Excusez moi, Munch…are you sure you’re on the right SDMB???
Best wishes,
hh