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PETROLEUM TOPIC FACT SHEET

Benzene is a naturally occurring hydrocarbon found in many substances including crude oil. It is also one of the many aromatics compounds formed during oil refining, particularly from reforming processes. Along with other aromatics like toluene and xylene, it increases the octane rating of petrol to the level needed by engines in order to provide acceptable fuel economy and performances.

The three main sources of benzene emissions associated with the use of petrol in motor vehicles are:

• Exhaust emissions - 80 to 90%.
• Evaporation from vehicle fuel tanks - 10 to 20%.
• Transportation, delivery and customer filling which together account for 3 to 6%.

Australian regulations requiring catalytic converters on all new cars since 1986, and the provision of small carbon canisters in the vehicle vapour recovery system have contributed to a progressive lowering of benzene in the atmosphere. This lowering has been further enhanced by the fitting of vapour recovering systems at oil terminals and service stations in large cities.

It has been estimated in the UK that the daily benzene intake of a resident averages 500 micrograms (that is half of one thousandth of a gram). Of this, half comes from food, while a 10 per day cigarette smoker takes in at least 300 micrograms, and someone filling a car with petrol, about 20 micrograms. The daily intake of Australian residents is likely to be similar to or lower than the levels in the UK.

Motorists driving in traffic are exposed to slightly higher ambient levels of benzene due to pick-up of exhaust gases and evaporative emissions through the car vent system. Catalytic converters will reduce this to the equivalent of a few micrograms per day.

Medical aspects

Benzene concentrations in the atmosphere can range from one part per billion (1 ppb) in natural bush land to 25 ppb at a service station. There is no evidence of any adverse effects on human health from typical atmospheric levels of benzene.

Only in cases where there have been frequent exposures in industrial situations to concentrations in excess of 1000 times greater than that typically found at a service station over a period of years, have adverse health effects - specifically, an increase in the incidence of myeloid leukemia - been associated with benzene. The current work place exposure limit in Australia is 10,000 ppb 8 hour Time Weighted Average (TWA). This limit is related to employee work place exposure. The general public are unlikely to be exposed to annual average levels of benzene approaching one thousandth of the occupational limits.

There is no evidence that the very low levels of benzene exposure associated with motoring are a risk to the public. No harmful health effects have ever been detected from the very low exposure levels to benzene in the air experienced by people refuelling or driving cars, or by people working or living near petrol stations. It is important to note that the incidence of acute myeloid leukemia does not vary between urban locations where there is more traffic, and rural locations, where there is less. Nor does there appear to have been any significant change in the incidence of acute myeloid leukemia over the past forty years despite a quadrupling of petrol consumption over this period.

The level of benzene in Australian petrol is legally limited to 5% by volume. The benzene content will vary, depending on the type of crude oil being processed and on the particular refining process involved. The Australian average benzene content of leaded and unleaded petrol is typically less than 3% and will remain so.

Future emissions of benzene

The total emissions of petrol related benzene have been falling in Australia since the introduction of ULP and the mandatory fitting of catalytic converters to all new vehicles since 1986. The catalytic converter eliminates up to 90% of benzene emitted from a petrol car exhaust. Additionally, there has been no noticeable increase in the average benzene level in Australia of either leaded petrol or ULP through this period.

Benzene: Implications of lowering lead content of petrol

The maximum lead content of leaded petrol in both NSW and Victoria has been lowered to 0.2 grams/litre as from the beginning of 1995 and in other States by the end of 1995, in accordance with the outcome of the Lead Round table Conference of July 1993. Some companies may elect to supply leaded petrol at even lower lead levels.

This reduction in lead content of petrol does not necessarily result in a higher benzene content in petrol. The Australian refiners advise that there will be little or no noticeable increase in benzene content of petrol with lead at 0.2 grams/litre. The average benzene content of petrol in Australia will remain close to current levels and well below general world standards.

The benzene level in petrol will vary slightly, but always within the legal limit, due to the constantly changing properties and quantities of the refinery streams used to blend the finished product. Reducing the lead in petrol level requires changes to refinery operation to maintain octane rating. Each refinery has a range of possible means of achieving this objective. By balancing these varied processes, the marginal increase in octane rating to compensate for the lower lead level can be obtained while, at the same time, maintaining benzene at close to current levels.