Junk is a type of edible (and harmful) object that appear in Hungry Shark World.
Appearance[]
There are multiple different types of junk bits including plastic bags, bottles, dollar bills and multiple items that were thrown into the water. All junk is surrounded by a small greenish cloud of pollution, making them quite easily noticeable.

A piece of junk ( in this case a plastic bag ) as it appears on the missions screen
How it functions[]
Junk is edible, but it's highly required to avoid eating it unless you need to eat it for a mission. Every time a shark eats junk it instantly looses a small bit of health and the health drain is increased for a split second, giving the accolade "Yuck!" It appears in every single ocean in the game and is really common, especially in the Pacific Islands and Arctic Ocean and South China Sea which makes it easy to accidentally lose health by eating it. When you are in a Gold Rush, eating junk gives you coins and does not harm you, so try to eat as much of it as you can, to clear the area for easier movement.
Junk can be absorbed by the Recycler Cannon and be fired back at humans or human made objects, where it disintegrates and cannot cause any harm.
Good Junk[]
Good junk, such as Dollar Bills, Cannibal and Bottles, give you coins when eaten. As they glow green too, you can easily mistake the two if you don't look.Ar