All internal combustion engines (e.g. cars, motorbikes, agricultural vehicles, ships) and industrial machinery need to be lubricated in order to work. Mineral or synthetic lubricants are used for this purpose.
During use, oil wears out and undergoes chemical and physical transformations that make it unfit for operation. This is why it needs to be replaced regularly.
When it is poured into the ground, it penetrates the soil and poisons the groundwater that provides water for drinking and irrigation.
When dispersed in water, it forms an impermeable film that deprives it of oxygen and kills all life.
When burned improperly, it releases pollutants into the atmosphere that can cause poisoning and illness.