MTBE
What is it?
In the UK, Methyl tertiary butyl ether (MTBE) is used as an anti-knock agent in unleaded petrol. It is also used as a therapeutic agent in the treatment of gallstones. There has been considerable media interest in MTBE in the USA, where its use to improve combustion and hence emissions from motor vehicles has been associated with contamination of water supplies. This has raised concern about possible contamination of water supplies in Europe.
The principle concern about MTBE in water is the taste and odour caused, even at very low concentrations (typically 5 to 10 microgrammes per litre). Toxicity effects do not occur until the concentration in water reaches much higher concentrations (milligrammes per litre). It may be assumed that even trace contamination of drinking water would be detected by its unacceptable odour.
What is the position in the UK?
The situation concerning the use of MTBE in California and the potential for contamination of drinking water is very different from the UK position. In the US there are much higher concentrations of MTBE in petrol. In addition, groundwater in California is often drawn from relatively shallow wells in hydraulic contact with the urban surface i.e. without a protective low permeability layer. This contrasts with the UK situation, where abstractions tend to be from deep, consolidated aquifers in rural settings. Also, in the UK groundwaters are frequently protected from direct contamination by impermeable clay or other layers.
The Inspectorate is aware of only one serious MTBE drinking water contamination event that occurred in the UK. This was in a source in East Anglia, adjacent to an airbase where fuel had been spilled. Activated carbon treatment was installed to remove the pollutant.
The Environment Agency is responsible for protecting the quality of groundwater. A survey of incidence of MTBE pollution of groundwater has recently been carried out by the Agency. The work suggests that under current usage conditions it is very unlikely that MTBE would cause problems like those in the USA.
What can you do to avoid contaminating drinking water?
Consumers carrying out home car servicing or degreasing operations sometimes need to dispose of petrol that has been used as a solvent. It is important to realise that even small quantities of petrol can contaminate large volumes of water. Petrol should not be tipped on the ground to soak away. This practice causes pollution of groundwater. It can also cause direct contamination of tap water if the service pipe is plastic. Petrol can soften and permeate polyethylene and PVC water supply pipes which allows the petrol and MTBE to contaminate drinking water. All solvents should be disposed of at a garage or other locations where solvent recycling points are available.
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Updated 11 July 2001
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