A cool thing about silicones is they complicate the processing of landfill gas. That gas is from bacterial decomposition of waste landfills, and is mostly methane + CO2. So burning it in small engines or turbines makes sense. But it also has silicon-bearing volatile compounds from decomposition of silicones, and if you burn those in an engine you fill it with particles of silica, which abrade surfaces and form glassy coatings on turbine blades.

An additional source of silicones in landfills is cosmetics, of which they form a substantial fraction.