A Council is urging residents to only put out appropriate items for recycling after an eight inch knife was left amongst plastic bottles.
Torfaen Council says a collector could have been seriously injured by the kitchen knife left in a plastic carrier bag in a recycling box in Cwmbran.
It was only when unloading the lorry that the knife was spotted poking out of the bag which also contained the bottles.
The incident comes just months after a collector received blood test results giving him the all clear after pricking his finger on a hypodermic needle left in a box in the Thornhill area of the town.
The collector, who was tested for HIV, hepatitis A, B and C and syphilis and works for the local authority's contractor Cleanstream, said the results ended months of anxiety over his health.
A Torfaen Council spokesman said: "We can't understand why someone felt putting out a knife like this for recycling was acceptable.
"Thankfully, only a small minority of residents contaminate their recycling with items like kitchen knives, needles, used nappies, sanitary towels, dog faeces and broken glass.
"We are relieved that nobody was hurt in this latest incident but cases like this highlight how important it is to only put out the correct materials in your black box."
The spokesman urged people to only put out newspaper and magazines, tins, can and aerosols, glass bottles and jars, plastic bottles and textiles.
Apart from textiles, which must be bagged to keep them dry, all other items can be put in loose.
If residents want to separate materials into bags they should use plastic carrier bags and not black rubbish sacks.
"The vast majority of residents do a fantastic job and they are very enthusiastic about recycling in the area," said the spokesman. "It's thanks to their efforts that we are the best performing recycling authority in South Wales."
For more information visit the Rubbish, Waste and Recycling| area of the website.