Problems also arise from imperfectly controlled incineration, which can produce harmful substances, especially where plastics are involved. There is evidence that, in addition to the long-known hazardous substances, some substances (often called endocrine disruptors) that do not reach the levels of toxicity, persistence and bioaccumulation in the accepted definitions of hazardous substances, can disrupt the endocrine systems of humans and animals, with adverse effects on their reproductive success, metabolism and behaviour. The use of the best practicable means to limit the creation of waste, discharges and emissions can help control these problems.