Since we are hearing of late so much about bioplastics in their various forms, it's interesting to contemplate a recent study by Dr. Amy Landis and her colleagues at the University of Pittsburgh. Dr. Landis' research team has been doing life-cycle environmental impact analyses, or LCA's (described here and here) for "bio-polymers" in comparison with petroleum derived polymers. The results are rather interesting.
Apparently, such items as fertilizer use, land-use diversion, and intensive pre-polymerization processing combine to make the bio-materials less environmentally friendly than many proponents suggest. And, after all, the petroleum-derived polymer industry really is pretty darned efficient.
The Pitt group's study found that polypropylene had the lowest life-cycle impact of the materials examined, followed by polyethylene. Then came PHA (polyhydroxyalkanoate) as the best of the bio-materials. (Vinyl and PET were at the bottom of the list.)
The study is ongoing, and caveats abound. First, a shift to cellulosic feedstocks may improve the performance of the bio-materials (switchgrass beats corn). Also, the study to date has not fully explored the "end-of-life" part of the LCA. Truly biodegradable polymers (if and when they materialize) might shift the balance.
Still, the point to be taken was nicely summed up by Dr. Landis: "Just because it's a plant doesn't mean it's green."