Plastics contain thousands of possible additives, many of which are toxic to the planet. Currently, manufacturers are not required to disclose which additives are present in their products. Any plastic can leach, depending on the conditions (light, heat) and what additives it includes.
Some plastics we know are toxic, such as #3, which is also known as PVC or vinyl. PVC contains phthalates and heavy metals. When burned plastic #3 creates dioxins that are released into the atmosphere.
Other plastics contain Bisphenol-A (BPA) a chemical that has been known to disrupt hormones, especially estrogen. It is know that exposure to BPA increases the likelihood of cancer and diabetes in humans.