Enhancing Organization in Marine Pollution Essay

Read the following passage excerpt from a student's essay about the effects of water pollution on marine life:

Water pollution poses a significant threat to marine ecosystems. The introduction of harmful chemicals into oceans disrupts natural habitats. Many species struggle to survive in contaminated waters. Not only do these chemicals poison the fish, but they also harm the entire food chain. Moreover, public health is at risk when contaminated fish are consumed by humans. The necessity for stricter regulations on industrial waste is clear.

Which of the following sentences, if added after the third sentence, would best enhance the organization of this paragraph?