What substances can used antifreeze contain?

Used antifreeze can contain a variety of substances, including ethylene glycol or propylene glycol, which are the primary antifreeze agents. Additionally, it may contain contaminants such as heavy metals (like lead or cadmium), silicates, organic acids, and other additives that were originally present in the fluid. Over time, used antifreeze can also accumulate impurities from the engine, such as oil, dirt, and rust particles. Proper disposal and recycling of used antifreeze are crucial due to its toxic nature and potential environmental impact.