Cambridge’s recycling contamination rate dropped to 4 percent last year from 11 percent in 2018, the city announced Thursday. The reduction saved the city more than $100,000 for the year,

Items such as plastic bags, clothing, electronics, and other items not accepted in curbside recycling are considered contamination. The city launched an effort to “Recycle Right” in June 2018 to get such contamination to below 7 percent from what’s collected in free curbside recycling from approximately 44,500 households. The campaign included monitoring and tagging of recycling carts on collection day, with more than 5,000 carts inspected in each neighborhood of Cambridge and more than 1,500 carts over several months “tagged with a friendly ‘Oops’ message because the cart had ‘medium’ or ‘high’ contamination,” the city email said. “The goal of these tags was to gently nudge and remind residents about how to recycle properly.” Postcards were also sent to each of the 4,000 households that had reports of high contamination.

There was also a three-phase campaign with ads on BlueBike Stations, MBTA bus shelters and A-frame sandwich boards and flyers; stickers for the lids of recycling carts; and a citywide mailer about waste services, including how to recycle properly. The city also worked with its curbside collection contractor to reject more bins for having contamination. By late 2019, the rate of contamination was already at 6 percent.