For those of us who spent most of our lives painstakingly separating plastic, glass, paper and metal, single-stream recycling is easy to love. No longer must we labor. Gone is the struggle to store two, three, four or even five different bags under the kitchen sink. Just throw everything into one dumpster, season liberally with hopes and dreams, and serve it up to your local trash collector. What better way to save the planet?

But you can see where this is headed.

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 don’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.

There’s some evidence that this contamination can be high enough that it ends up counteracting any increase in the volume of material you got from the ease of single-sort. A 2002 study, for example, compared five different methods of recycling collection in the city of St. Paul, Minnesota, with the city’s then-current multi-sort system. Single-stream recycling produced the highest rate of loss at the processing stage — essentially, the most stuff put in recycling bins that couldn’t actually be recycled. Compared with the existing system, gross tons of recycling collected at the curb increased by 20 percent, but there was a net decrease of 12 percent in tons of material that left the sorting facility ready for recycling.

When more recyclables means less recycling Comparison of recycling systems to a baseline multi-stream, biweekly collection system over 14 months in St. Paul, Minnesota, in a 2002 study % change in tons from baseline Stream type Collection Frequency collected actually recycled % Lost due to contamination Net Cost Per Ton Multi-stream Biweekly +6.2% 4.5% 1.6% $45 Dual-stream Biweekly +7.3 -4.5 10.9 $57 Dual-stream Weekly +26.1 12.5 10.8 $66 Single-stream Weekly +20.8 -12.2 27.2 $78 “Multi-stream” refers to a system where participants have to sort multiple kinds of recycling materials at home, before collection. “Dual-stream” systems require separation of paper/fiber material and containers. “Single stream” recycling is sorted after collection. Source: Eureka Recycling

That study is old, and recycling data is difficult to get because much of the relevant information isn’t publicly reported, and the reports we do have aren’t generally peer-reviewed. But there’s other research that supports the basic concept that single-sort systems have high enough rates of contamination to potentially offset gains in participation. A 2004 report compiled for the American Forest and Paper Association found that single-stream increased the net tonnage of paper ultimately recycled only by 1 to 3 percentage points, a small enough gain that it could easily tip in the other direction. Meanwhile, a British report from 2008 found that you can collect roughly the same percentage of potentially recyclable materials from customers whether you use a single-stream system or one that separates paper goods from containers (so two recycling bags under the sink, not five). And that’s before you account for the lower contamination rates generally found in a dual-stream system.

The risk of contaminated recycling offsetting gains in recycling participation has become a real issue over the past five to 10 years as single-stream systems have grown in popularity, said Bernie Lee, a commodities research analyst with the Institute of Scrap Recycling Industries, a trade association. And multiple analyses have shown that single-stream systems also cost more to operate, because of the increased expenses associated with sorting and the lowered value of contaminated recyclables when it comes time to sell.

So why is it so popular? “It’s cost-effective for the waste haulers,” Lee said. Single stream makes it easier and cheaper to collect recycling — you need fewer staffers to operate fewer trucks, which collect recycling more efficiently, and require less fuel to run. Brent Bell, a vice president at Waste Management Inc., a national recycling hauler, agreed with that. In fact, other experts told me that the lower collection costs had, in some cases, even allowed companies like Waste Management to pay communities to haul the recycling away, instead of the other way around.

But those kind of benefits were dependent on there being a place that recycling haulers and sorters could easily sell sorted material that still had high contamination rates. That place used to be China, but that changed last January when China increased its standards and stopped accepting some types of material altogether. Other countries have picked up some of the slack, Lee told me. But about half the recycling that China used to buy has no buyer today. “The only presumption is that it would have to go to the landfill,” Lee said.

Part of what made single-stream recycling such a good deal was the Chinese market for contaminated recycling. Without that, more potentially recyclable items are ending up in the trash and the economic picture has changed. Even Waste Management, which Bell told me was actually able to find other buyers for all of what it once sold to China, is changing its practices. In 2008, the city of Lake Worth, Florida, signed a contract with Waste Management where the city was paid $10 per ton of single-stream recycling collected. In 2018, when the contract was up for renewal, the terms would have shifted to the city paying Waste Management $85 a ton instead. The city opted to change to a dual-stream system operated by the county.

And Lake Worth isn’t alone. Several other communities have shifted away from single-stream in the past year, at least partly in response to economic changes brought on by the Chinese regulations. Other communities have increased surveillance of what gets left in single-stream bins — and fines for people who violate the rules.

Single-stream isn’t the only cause of higher contamination rates. New kinds of plastic that clog up recycling machines also play a role, Lee said, and so does our love affair with Amazon — and the resulting increase in recycled cardboard boxes contaminated by various tapes, glues and inks. But it’s a big factor. And with China no longer buying — and other countries considering similar restrictions — we’re going to have to make our recycling cleaner. That means either less single-stream recycling or more public education and more stringent use of single-stream systems. Either way, you can expect recycling to get at least a little less convenient.