Related Clues:

• One needing rehab
• Consumer
• One who's in it for himself
• Web visitor, e.g.
• Earth-friendly prefix
• Prefix with sphere or system
• Green, in a way
• Environmentalist's prefix
• 'Foucault's Pendulum' author
• Nonpolluting
• Author Umberto
• Computerphile
• See 36-Across
• Green's prefix
• Junkie