Marketplace: Steve Chiotakis: And on this Christian holy day, this weekend marks the end of Lent. It’s a time when many Christians stay away from meat, sweets or alcohol. But some have gone on a 40-day eco-fast. From the Marketplace Sustainability Desk, Jennifer Collins reports. Jennifer Collins: For lent this year, Mary Hetherington went on a carbon fast. She bought organic produce, she paid for a high-level cleaning of her furnace, and she learned a lesson: Mary Hetherington: It’s a …