A decade ago, most towns required residents to separate their recyclables into multiple bins. But in an effort to boost recycling participation, many municipalities switched to a single-stream system, where everything is commingled in one bin, to be sorted later at recycling facilities and the public has become lazy. In hindsight, it’s turned out to be a significant problem because many recycling cans are now contaminated. Some towns have instituted a “tag and leave” program, leaving contaminated loads at the curb and tag them with an explanation for the homeowner when they can see plastic bags or Styrofoam or something else not allowed in your recycling. Studies show that’s the only thing that changes behavior. “Over the past 10 years New Jersey has really hit a recycling crisis,” said Randall Solomon, executive director of Sustainable Jersey. “I’d say we as a state and as a country — even the world — are at a critical juncture.”