The chemicals found in used mineral-based crankcase oil vary depending on the brand and type of oil, whether gasoline or diesel fuel was used, the mechanical condition of the engine that the oil came from, and the amount of use between oil changes. Used oil is not naturally found in the environment. Used mineral-based crankcase oil enters the air through the exhaust system during engine use. It may enter water or soil when disposed of improperly. The hydrocarbon components of the oil generally stick to the soil surface.
Some hydrocarbons evaporate into the air very quickly, and others evaporate more slowly.
Hydrocarbon components of the oil that enter surface water bind to small particles in the water and eventually settle to the bottom. Hydrocarbons from used mineral-based crankcase oil may build up in shellfish or other organisms. Some metals in used mineral-based crankcase oil dissolve in water and move through the soil easily and may be found in surface water and groundwater. Animal testing is sometimes necessary to find out how toxic substances might harm people or to treat those who have been exposed. Laws today protect the welfare of research animals and scientists must follow strict guidelines.