[barrkel]

The tax should still be on the purchase price. If essential goods end up too expensive for poor people, then the answer is to raise income levels for poor people via some kind of redistribution.

In order to solve the problem systematically, incentives need to be aligned so that desired global collective outcomes emerge from local individual choices.

If the cost isn't on the purchase price, there's little incentive on consumers at the point of purchase to choose a product with a cheaper disposal cost. Disposal is geographically and temporally remote; and if you're poor, you can economize on it by cheating (littering, fly tipping, illegal burning, man with a van who takes the problem off your hands, etc).