Air lead, blood lead and travel by car.

Evidence on the relevance of lead in petrol to lead in blood has come from two main sources. Cross sectional studies of blood lead levels in population samples and in the air to which they are exposed suggest that petrol makes only a very small contribution. However longitudinal studies in the USA in which changes in lead levels in petrol and changes in blood lead have been studied suggest that petrol makes a substantial contribution to blood lead. The possibility that this discrepancy might be explained by the exposure of subjects to very high levels of lead when travelling in motor vehicles is examined, and rejected.