Actor and environmental activist Adrian Grenier is perhaps best known for his lead role in the HBO series Entourage. But he has also made a name for himself at the forefront of the international fight to reduce the world's reliance on single-use plastics, in order to decrease harm to the ocean, wildlife, and human health.

Grenier has been working on educating the public about the problems with plastic straws and other throwaway items through his foundation Lonely Whale. He is also a celebrity ambassador for the United Nations World Environment Day, which takes place Tuesday. Grenier is helping the UN spread the word about the impacts of single-use plastic, which is the focus for this year's annual World