Unleaded petrol: a solution or a problem?

February 8, 1995

By Richard Giles

Evidence is accumulating that unleaded fuel could be more damaging than leaded. Unleaded fuel may be causing new waves of cancer and making a profound contribution to environmental degradation.

While declines in the amount of lead in the air are positive, the alternative to lead is not pretty either. Unleaded petrol costs more to make than leaded fuel, results in the use of more oil and creates more pollution, because of the aromatics.

Unleaded fuel is 50% aromatic additives — they are the replacements for lead. They are dimethylbenzene, mesitylene, toluene, xylene and benzene. Each is a carcinogen. They are called volatile organic compounds (VOCs). Tests at the Institute of Oncology in Bologna, Italy, found that fuel additives benzene, toluene and xylene produced cancerous tumours when ingested or inhaled. Benzene is particularly harmful, and is linked with childhood leukemia.

Recent statistics from Sweden in 1993-4 show that service station workers had unexpectedly high rates of leukemia. Unleaded fuel being pumped into a tank releases aromatic compounds. You are at high risk from benzene and other VOCs at the service station. It is most important to avoid inhaling petrol fumes at the service station and at home.

The maximum recommended exposure to benzene is one part per billion (ppb) over 8 hours. Recent reports from Sydney show that levels of benzene in the Sydney CBD approach 25 ppb in winter and 10 ppb in summer. The worst levels are 2500% over the recommended safe limits.

The standard text Introduction to Organic and Biological Chemistry by S. Baum states: "Repeated exposure to benzene leads to a progressive disease in which the ability of the bone marrow to make new blood is eventually destroyed".

Engines which are unsafe with unleaded petrol include chainsaws, two-stroke and four-stroke mowers, outboard engines and other small motors. None of them have catalytic converters and are therefore totally unsafe. Since all are used within a very small range of the personal environment, users are at serious risk.

A car's catalytic converter removes the pollutants from the fuel as it is burnt. So no benzene is released if a car has a properly functioning catalytic converter — except that they do not work until they reach a temperature over 400 C. Before that, aromatics in fuel are not converted. The most dangerous time to stand near a car using unleaded fuel is thus when it is warming up in the family driveway or garage. A family is therefore most at risk at home.

Vehicles not fitted with catalytic converters do not process the aromatic additives in unleaded fuel. The official recommendation for the use of some unleaded fuel in some pre-1986 vehicles is dangerous for that reason.

In 1994 a cross-party group of British MPs called on the UK government to ban super unleaded petrol. The UK Transport Select Committee concluded that the dangers of all unleaded petrol far outweighed the benefits of reduced lead levels and called for an inquiry into why the public was being advised to use it in cars not fitted with catalytic converters. It urged the UK government to scrap sales of ULP by 1996. The government ignored the report.

Anti-pollution gear on modern vehicles lasts about a year. After that, catalytic converters deteriorate rapidly and must be renewed. Their average life span is about 50,000 kilometres.

Lead is in petrol to raise octane ratings, increasing engine efficiency. The lead is subject to 2000-3000 degree heat and is baked like a brick. So when the lead particles go out the exhaust, they fall to the ground three to four metres away, being much heavier than air. Tests on baked lead particles with various acids show they do not dissolve. They are also not absorbed into the lungs like lead dust. Lead dust does not come from car exhausts.

Figures on lead levels in blood from 1933 until 1985 show a steady decline. Lead began to be added to petrol in 1925 and peaked in 1970, yet lead levels in blood do not show a corresponding rise. Decreases in lead levels in blood have been attributed to the reduced use of pewter, the gradual phasing out of lead solder in cans and the replacement of lead water pipes carrying water in our cities and towns.

Suggestions that the decision to move to unleaded petrol was based on commercial concerns are worth considering. The chief reason was that dry catalytic converters became very quickly clogged with lead particles and ceased working.

We need a rethink on unleaded petrol. More serious environmental problems than we had pre-1986 could be looming. Cancer and leukemia rates may rise as a result of unleaded petrol. This government decision may have been made under pressure from oil company interests rather than from environmental concerns.

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