What is used oil?

Used oil is the lubricating oil that is drained from machinery, engines, gearboxes, hydraulic systems, turbines and air compressors, once it has become dirty and contaminated from usage including:
• Used lubricating base oil that has deteriorated and degraded to acids.

• Used oil that is contaminated with wear debris.

• Used oil in which the additives have decomposed into other chemical species

• Used oil that is contaminated because process fluids, degreasers and solvents have mixed into it.
Used oil contains wear metals such as iron, tin and copper as well as lead from leaded petrol used by motorists. Zinc arises from the additive packages in lube oils. Many organic molecules arise from the breakdown of additives and base oils.
The molecule potentially the most harmful is the polycyclic aromatic hydrocarbon (PAH) such as benz(a)pyrene and chrysene. Petrol engines generate the most PAH molecules per 1000km, with diesel engines below that and 2 stroke engines generating the least amount of PAH.