E-waste should never be sold as trash to rag-pickers as it may end up with unorganised recyclers who basically burn main parts to extract precious metals. This causes release of extremely toxic substances called dioxins and furans.
E-waste should also not be dumped in a landfill. Even in small doses, these materials can contaminate soil as well as drinking water. Landfills are also prone to uncontrolled fires which can release toxic fumes.