Deposition in the lung and uptake to blood of motor exhaust labelled with 203Pb.

Inhalation of airborne lead from automobile exhaust is a significant source of intake. In these experiments a radioactive isotope of lead was used to label tetraethyl lead consumed in petrol engines. The resulting aerosols were inhaled by human volunteers to determine the percentage deposition in the lung, the pattern of removal from the lung and the resulting levels in the blood and excreta. Deposition in lung was shown to depend on particle size, varying from 40% for fresh, highly diluted aerosols to 14% for mature, aggregated aerosols, at a breathing rate of 15 breaths per minute. For aggregated aerosols the influence of rate of breathing, tidal volume and reserve volume was investigated. Uptake from the lung was rapid (T 1/2=6.6 h) and virtually complete with little, if any, ciliary clearance. Fifty per cent of the labelled lead remained in the blood, the concentration peaking after 2 days and subsequently declining exponentially (T 1/2 = 16 d). Total excretion was of the order of 1% of the intake per day up to 15 days.