Until recently Tetra Ethyl-Lead or TEL was a popular additive to petrol. TEL was added to petrol to improve the octane rating of petrol. TEL is a non biodegradable substance that easily dissolves in petrol and reduces ?knocking? in the engine. Not only does TEL allow a higher compression ratio in engines, it also improves the efficiency of engines. TEL was first used as an additive in the US in the 1920s. The effectiveness of TEL as an additive was discovered way back in 1921, what is interesting to note is that TEL was so toxic nearly a dozen researches died while experimenting with TEL.



Despite its known toxicity, Exxon and GM (General Motors) created the Ethyl Petrol Corporation to manufacture and market TEL (the year was 1924). What is shocking is that when the EPA finally started proceedings to phase out TEL in 1974, they were sued by the Ethyl Petrol Corporation. It was only when the EPA won the law suit that the phasing out of TEL began. In fact, the European Union was even slower to react, and only in the year 2000 was TEL completely phased out as an additive to petrol by the European Union.

The reason why TEL has been ?phased out?, is that on combustion TEL forms Lead Oxide. The Lead Oxide then reacts with Ethylene Dibromide (another petrol additive). Then end result of TEL combustion is Lead Bromide a highly volatile and toxic gas. Lead Bromide not only causes air pollution, but it also leaches into the soil surrounding highways and roads. In addition, the lead in TEL damages catalytic converters that have been standard equipment for US cars for many years now. Whatever the reasons for phasing out TEL, TEL is a highly toxic substance and TEL has posed a serious environment and health risk over the years.

TEL free petrol is now available all over the world, as of today only a handful of countries actually sell leaded petrol (the term ?leaded? indicates the petrol still has TEL). Even though TEL has been eradicated as an additive, even today the concentration of lead in soil surrounding roadways is very high. Aviation fuel and high performance fuel still have TEL. In fact, there has been no suitable replacement for TEL in aviation fuel and every year a small amount of TEL is still produced to be added to aviation fuel. Similarly, TEL is also a standard additive in high octane fuel for racing.

As of 2007, unleaded petrol is available throughout the world, and the only countries in which leaded petrol is extensively used are Yemen, Afghanistan and North Korea. Leaded petrol is still available in parts of Northwest Africa, Europe, Commonwealth of Independent States (CIS), Iraq, Jordan and the Palestinian territories. The use of alternative additives and high quality petrol has meant that slowly but surely the phasing out of TEL as an additive in petrol has been a success, however more work needs to be done to completely eliminate TEL from all type of fuels.

TEL alternatives

In order to effectively phase out Tetra Ethyl-lead, the first requirement was finding a suitable replacement for TEL. Additives like Methylcyclopentadienyl Manganese Tricarbonyl (MMT) are in use in Canada, but the use of MMT has been banned in the US. Even in 1921 it was established that Ethanol and other additives can be used as anti-knocking agents, but GM and Exxon chose to pursue TEL for purely commercial purposes. Additives like Ferrocene are also known effective anti-knocking agents; however recent improvements in the quality of petrol have meant that very soon there might be no need for any anti-knocking agents at all. Ethanol is one of the leading anti-knocking agents available today and newer anti-knocking agents are being developed and tested by various countries.