The nastiest of those potential contaminants isn't your polypropylene but rather PVC (aka plastic No. 3). Though it's increasingly rare in the United States due to concerns over dioxin emissions during manufacture, PVC is still prevalent enough to ruin many a load of otherwise recyclable PET. The stuff is the bane of recyclers everywhere: A single PVC bottle can irrevocably contaminate an entire 800-pound load of otherwise desirable PET, rendering it unfit to be made into new products—PVC forms acids when mixed with PET, and those acids can make the recycled plastic unacceptably fragile. Because of this danger, many recycling facilities now employ machines such as FlakeSort, which analyzes the PVC content of processed plastic "flakes" before they're sold on the open market.
Those flakes are rarely turned into new food-grade products but are "downcycled" into pipes, fence posts, and picnic tables—exactly the sorts of products that recycling facilities reject during their initial screenings. So when these post-consumer items are no longer wanted, they're ultimately destined for the landfill or for an incinerator in Guangdong Province.
Despite its labor-intensive and relatively inefficient nature, plastics recycling still makes long-term sense. The EPA estimates that making a ton of plastic out of used PET bottles saves 55.9 gigajoules of energy over manufacturing a ton of plastic from scratch. And in 2005, Britain's Waste Resources and Action Programme analyzed (PDF) 60 different life-cycle scenarios for plastics. The organization concluded that recycling was invariably superior to landfilling, in terms of net carbon emissions. Recycling was clearly preferable to incineration, meanwhile, in more than 76 percent of the scenarios. It bears noting, however, that the WRAP study doesn't seem to have factored in the energy used to transport plastics to overseas incinerators nor the possibility that those incinerators lack proper emissions safeguards. (Environmentalists fear that burning PVC, in particular, can lead to toxic emissions, and that even ostensibly safer plastics contain heavy metals in their pigments.)
The equation tilts more heavily in recycling's favor once you consider the recent rise in oil prices. About 8 percent of the world's oil supply goes toward making plastics—half into the actual feedstock and half to power the manufacturing plants. With crude futures currently hovering around $120 barrel, there's a lot of incentive for companies to figure out how to use recycled flakes in lieu of virgin plastic. If this trend continues, maybe they'll even start jonesing for your yogurt cups.
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