In the Planet Protectors eBook, three friends notice that changes have occurred in their local park over the past five years. These friends want to figure out what has happened to the park and why these changes have occurred. In order to do this, they explore how humans have contributed to the air, land, and water pollution of the park. One way in which they investigate these changes is by conducting tests for environmental pollutants. They also learn how deforestation impacts the environment and adds to the effects of pollution.