Poisonous substances that contaminate recycling materials are classified into two categories. One includes is poisons to the living body, such as lead and arsenic, carcinogens and endocrine disruptors, pathogenic germs and prion. The other includes poisons to materials for industrial use such as Cu in Fe and Ni in Cu for metals, and poisons generated in during use and different kinds of polymers for plastics. The poisonous substances can be eliminated by waste treatment or through natural circumstances. However, such poisonous substances recycle and accumulate to a higher level in a recycling than in a non-recycling society. The concentration of Cu, which is a poison for steel, increases with the passage of time and becomes higher by recycling, thereby influencing the recycling system itself. The characteristics of plastic, inorganic glass and industrial products are discussed from the same point of view.