Why does petrol contain lead?
The addition of small quantities (around 0.1 to 0.4 g/litre) of lead (in fact, lead salts, or TEL “tetraethyl lead” and TML “tetramethyl lead”) improves petrol resistance to detonation in a cost-efficient way. Additionally, it proves beneficial in the delicate valve contact areas in the cylinder head, where lead deposits have a “repairing” and lubricating effect. Clearly, lead is not subject to combustion along with petrol, so most lead ends up being disposed of through the exhaust. In the course of the last decade, the poisonous effect of lead on the environment was discovered, and engines started to be equipped with chemical catalysts. These devices, however, are by construction very vulnerable to lead: therefore, lead was gradually banned and today, it is no longer present in petrol.
