We have all done it: a greasy pizza box, a disposable coffee cup, the odd plastic bag. Sometimes, we want things to be recyclable, so we put them in the recycling bin.

Waste managers often call this wishful or aspirational recycling. But, unfortunately, putting these objects in with the rest of the recycling can do more harm than good. While rules differ in every municipality (check your local recycling website to find out what’s acceptable), we have picked out some key offenders to keep in mind.

Too many of these items will contaminate a batch of recycling. That means waste managers might not be able to find buyers for the materials — especially now that China, one of the world’s main importers of recyclable waste, has said it will reject shipments that are more than 0.5 percent impure. Contaminated loads could be sent to the landfill instead.