WalMart is beginning to switch from petroleum-based to corn-based plastic packaging. The first substitution, starting November 1st, involves 114 million clear-plastic clamshell containers used annually by the retailer for cut fruit, herbs, strawberries and brussel sprouts. The eco-effectiveness of this move must be weighed against the fact that the plastic will come from NatureWorks, a division of Cargill Dow. The parent company, Cargill, is a world leader in genetic engineering, and has come under fire for its use of genetically engineered corn. See more information about this issue here. Notwithstanding this, the adoption of this eco-friendly packaging at WalMart has the potential to mandate packaging change in the consumer products world. So it's a mixed bag in terms of environmental benefits.