If you're talking about the amount of litter:
* More litter: This is the most straightforward option.
* Greater litter: This is a more formal way to say "more litter."
* Heavier litter: This implies a larger quantity or weight of litter.
If you're talking about the quality of litter:
* Dirtier litter: This implies that the litter is more untidy or messy.
* Worse litter: This is a more general term that could refer to any aspect of the litter that is considered undesirable.
If you're talking about the impact of litter:
* More harmful litter: This implies that the litter is more damaging to the environment or public health.
* More impactful litter: This implies that the litter has a greater effect on the environment or public health.
Ultimately, the best comparative word for "litter" will depend on the specific context of your sentence.