A water pollution expert gave a speech at a local gathering. Read this excerpt from the speech. What is its purpose?

Water pollution is a growing threat to our environment. Not only does it harm aquatic creatures, but it can lead to serious health problems in humans. When toxic waste from industries is dumped into bodies of water, the pollutants contaminate a variety of fish and shellfish. When consumers eat seafood contaminated by toxins, they risk being exposed to a variety of toxic heavy metals.