LED filament lamps don't contains plastic, but what about the driver? It is still there, and its components have toxic materials, and the LED themselves also have toxic materials. All of these, still causes environment pollution when manufactured, disposed or even being recycled.
Not that much. The LED chip materials may be toxic in their pure form, but it is very hard toextract them from the finished LED even when you would intentionally do so, it will never release by itself.
The drivers are extremely simple bridge rectifiers and linear constant current source, both quite small chips, with some mg of silicon. The toxic elements are there, but in concentrations of barely 1ppm in the silicon itself, so we are talking about nanograms total quantity. Natural occurrence of these elements is way higher (e.g. as normal contaminants of practically all technical metals we use).
With manufacture the presence of these materials is concentrated, but these sites make so huge production of the final products, there are just few such sites on the Earth. Fewer than e.g. nuclear power plants filled with tons of high activity radioactive materials in their reactors. And there is very strong risk management on these installations, so the total environmental impact from contamination is nearly zero. The Chernobyl, Tokaimura or Fukushima (the most severe civil nuclear contamination release events) disasters already counted in, the radioactive and poison release from e.g. coal burning soot (natural contaminants present in the available coal) is still many orders of magnitude greater in total sum globally...