Sure! Here are the rewritten sentences using "if" or "unless":

1. If you litter, the environment will get dirty.
2. Unless we recycle, the amount of waste will increase.
3. If we do not stop using plastic bags, pollution will continue to harm animals.
4. If factories release harmful gases, the air will become polluted.
5. Unless people use public transportation, carbon emissions will rise.
6. If we save water, we will help conserve natural resources.
7. Unless we plant more trees, the air quality will not improve.
8. If everyone picks up trash, the streets will be cleaner.
9. Unless we reduce energy consumption, pollution levels will remain high.
10. If companies follow eco-friendly practices, the Earth will be healthier.