>that piece of the graph showing that 22 billion tons is discarded into the environment almost seems unbelievably high. There must be some caveat to that figure right?

A quick google search says oil consumption in 2015 was 9.3x10^7 barrels and a barrel weighs 3x10^2 pounds so if we used 100% of our 2015 oil consumption to make plastic which comes out about three orders of magnitude short. Less than 5% of oil production is used for plastic, more than making up for any increase in tonnage from other ingredients (mostly nitrogen and/or oxygen) in the plastic.

So yeah, there's something in that statistic that got lost in translation.