There are some medical/psychological conditions that cause this problem, but many children go through this stage naturally. I have a sister that went through a stage of eating all the toothpaste, scent and talcum powder in the house as a toddler. She grew up just fine. Note - toothpaste is poisonous if eaten in quantity so it should be kept out of reach of small children.
rebekahELLE posted a link to the article that presents as much as I know about eating non-food items. Put everything non-food he eats out of his reach or lock them up. Then take him to your doctor as soon as you can. If his parenrs are in the picture, persuade them to help you attack this condition. He may accidentally kill himself with poisonous liquids if he drinks any liquid.