https://phys.org/news/2018-05-recycled-electrical-products-hazardous-chemicals.html

Now scientists at the University of Plymouth have shown that a combination of the growing demand for black plastic and the inefficient sorting of end-of-life electrical equipment is causing contaminated material to be introduced into the recyclate.

This is in part because despite black plastics constituting about 15% of the domestic waste stream, this waste material is not readily recycled owing to the low sensitivity of black pigments to near infrared radiation used in conventional plastic sorting facilities.