Despite all those blue bins, Americans reuse only a small portion of the plastic that is produced. (Alla Dreyvitser/The Washington Post)

From an environmental perspective, the only thing that feels good about plastic is the recycling icon found on so many items. Those three arrows, feeding each other in an endless triangle, assure us that as long as we toss our water bottle or food container into a blue bin, the system is self-sustaining.

Taken literally, the symbol is quite misleading. Or, as Timothy Gutowski, a professor of mechanical engineering at MIT, told me: “If plastic recycling is a loop, it’s a pretty leaky loop.”

Even if we could turn every pound of plastic we use each year back into raw plastic for the next year, we’d still need to produce 11 million tons of new plastic to satisfy the worldwide growth in demand, according to data from the industry group Plastics Europe. Plastic is made from fossil fuels, so you can put that number into context by considering that 11 million tons of plastic requires us to divert 74 million barrels of oil from making energy to producing plastics.

Ready for the truly depressing part? Despite all those blue bins, we recycle a pathetically small proportion of the plastic we consume. The United States manages to recycle 7 percent of its plastic. Some of the rest is locked up in long-term uses such as home insulation, but most of it ends up in landfills.

“All forms of plastic are technically recyclable,” says Patty Moore, head of Moore Recycling Associates. Her company, based in Sonoma, Calif., helps businesses and governments recover recyclable materials. “Unlike paper, which has fibers that break down during the recycling process, plastic is made of long polymer chains that can be used and reused indefinitely.”

If plastic is so easily recycled, why are we so bad at it?

First, recovery is a problem.

“Plastic is used in small quantities in many products,” Gutowski notes. (Take a look around you. It’s probably easier to count the products that don’t include plastic than those that do.) It’s impractical to strip the plastic out of every consumer good.

More important, the recycling process involves significant loss of material. To understand why we recycle so little plastic, let’s hitch a ride through the recycling process on an empty bottle of ketchup.

Our first stop is the materials recovery facility. Until recently, human hands separated plastic, paper and metal when it came in. More-modern facilities feature robots that can distinguish the different materials and push waste into the appropriate container. The machines are far from infallible, though, and still require humans to clean up the robots’ mistakes. Even so, experts say too many batches of recycled goods are ruined by improper sorting and contamination.

Once our ketchup bottle has been segregated with the plastics, it will probably pass down a conveyor belt again as a machine separates different kinds of plastics. Most plastic food bottles are polyethylene terephthalate, or PET. But there are several other kinds, including polyvinyl chloride, or PVC, which is used in clothing, tubing and pipes. Even a small amount of PVC can destroy an otherwise salable batch of recycled PET, which puts a lot of pressure on the machine to be accurate. This is usually attempted with an infrared light, which is bounced off the surface of the plastic. The machine identifies different plastics by the light they reflect, but, again, mistakes are made.

Once the sorting is done, there is another opportunity for loss.

A plastic item, Gutowski says,“usually contains lubricants, colorants, fillers, antioxidants and other additives that make it impossible to return the plastic to its original quality.”

Orange or blue bottles of laundry detergent, for example, can be recycled only into darker-color material, unless prohibitively expensive chemical means are used to remove the dye. Our ketchup bottle, although clear, may contain a layer of non-PET plastic to prevent diffusion of oxygen into the product.

Such additives make it difficult for a recycler to know how useful a batch of plastic will be until it runs through the process, and plastic is regularly tossed aside because of chemical pollution. If our ketchup bottle makes the grade, it will be shredded, washed and offered for sale as pellets that can be used to make more ketchup bottles or other plastic materials.

Could we be doing better? It depends on economics and other contextual factors. Several Northern European countries recycle more than 30 percent of their plastic, because they have government subsidies and limited landfill space. In the United States, the price of oil will probably be a major factor. The more it costs to buy oil — the main ingredient in plastic — the more appealing recycling, and research to improve recycling technology, will become.