1. Oceans are currently a big dumping ground for tons of toxic waste and sewage. (waste, packing)
2. There are no more than two hundred and fifty species of sharks in the world. (species, kinds)
3. Storms and heavy rains often cause great damage to property. (damage, loss)
4. Some factories and plants release poisonous substances into the atmosphere. (increase, release)
5. People are not doing their best to avoid an ecological catastrophe. (avoid, prevent)