In a study of childhood cancer and possible exposure to benzene from traffic and petrol stations Harrison et al 1 found a non-significant increase in childhood leukaemia. In their conclusion they state that “… the data are overall rather reassuring in showing that any such effect, if real, is likely to be small in magnitude”. We think that this conclusions cannot be drawn from such limited material.

Firstly, they merge all types of leukaemia, whereas studies in adults have indicated that non-lymphocytic leukaemia is most strongly associated with benzene. An ecological Swedish study found an association between car density and NLL but not with other types of leukaemia or lymphoma.2

Secondly, the misclassification of exposure may be substantial in the study by Harrison et al. In Sweden wood burning makes a major contribution to the exposure to benzene in some areas. Probably the burning of other fuels for heating will also contribute. Children are transported in …

Professor R M Harrison