Americans love convenient recycling, but convenient recycling increasingly does not love us. Waste experts call the system of dumping all the recyclables into one bin “single-stream recycling.” It’s popular. But the cost-benefit math of it has changed. The benefit — more participation and thus more material put forward for recycling — may have been overtaken by the cost — unrecyclable recyclables. On average, about 25 percent of the stuff we try to recycle is too contaminated to go anywhere but the landfill, according to the National Waste and Recycling Association, a trade group. Just a decade ago, the contamination rate was closer to 7 percent, according to the association. And that problem has only compounded in the last year, as China stopped importing “dirty” recyclable material that, in many cases, has found no other buyer.

Most recycling programs in the United States are now single stream. Between 2005 and 2014, these programs went from covering 29 percent of American communities to 80 percent, according to a survey conducted by the American Forest and Paper Association. The popularity makes sense given that single-stream is convenient and a full 66 percent of people surveyed by Harris Poll last October said that they wouldn’t recycle at all if it wasn’t easy to do.

Some experts have credited single stream with large increases in the amount of material recycled. Studies have shown that people choose to put more stuff out on the curb for recycling when they have a single-sort system. And the growth of single-stream recycling tracks with the growth of recycling overall in this country. But it also pretty closely tracks with skyrocketing contamination rates.

Some of that is on us, tossing things in the bin that either doesn’t belong there or should have gone in the trash can to begin with. “We get a lot of diapers,” said Anne Germain, vice president of technical and regulatory affairs with the National Waste and Recycling Association. There are also electronics and batteries, plastic grocery bags and Christmas lights — all of which can be recycled, but only through specialty drop-off programs, not the curbside bin. There are perfectly recyclable cans and paper coated in food, grease or cleaning fluids that render them unrecyclable. There are plastic bottles full of glass syringe needles that break open at the sorting facilities like a piñata from hell.

But some of the problems with contaminated recycling are endemic to the process of single-sort itself, said Susan Collins, executive director of the nonprofit Container Recycling Institute. “The trucks are constantly compacting, smashing the materials together,” she said. “The glass breaks and shards get into the plastic and the paper. Aluminum cans and plastic bottles that get smashed have the same profile as the paper does.”

And all that means that the facilities where your curbside recycling goes to be sorted have more trouble, well, sorting it out. These facilities use machines to separate different types of materials from one another. The machines sometimes can’t tell the difference between a flattened water bottle, a well-squashed tin can and a piece of paper. One out of 6 bottles and 1 in 3 cans end up sorted and shipped out wrong, Collins told me. And the machines can’t un-grind glass shards from the fibers of a cardboard box or pick tiny bits of paper and plastic from piles of half-broken glass. “By the time the so-called glass gets to glass processing facility, it’s really glass mixed with 30 to 50 percent other stuff, which is trash,” Collins said.

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