Uptake of lead by inhalation of motor exhaust

Tetraethyl lead was labelled with $^{203}$Pb, added to petrol, and burnt in an engine. The exhaust aerosol was inhaled by volunteers, usually after it had been stored in a box, but in a few experiments directly, a few metres downwind of the engine. The percentage deposition in the lung, uptake to blood and excretion of the labelled lead were measured. The percentage deposition in the lung depended on the length of the respiratory cycle. For a 4s cycle (15 breaths/min) the deposition was 35 $\pm $ 2 (s.e.)%. Most of the $^{203}$Pb was removed from the lung with a half life of about 6 h. About half of the amount deposited in the lung was in the blood at 50 h after inhalation. A similar fraction was in the blood at the same time after injection of $^{203}$PbCl$_{2}$ in saline solution. From this and other evidence it is deduced that most of the $^{203}$Pb passed from the lung to the blood plasma. About half was removed to bone and other tissues, and half became attached to red cells. From about 72 h onwards, the amount of $^{203}$Pb in blood declined with a mean biological half life of 16 d. Assuming that the same half life applies beyond the period for which measurements were made, the results can be used to predict that continuous (24 h/d) exposure to 1 $\mu $g/m$^{3}$ of exhaust lead over a period of months will given an average contribution of about 1 $\mu $g/100 ml to blood lead. Results of other work on experimental and industrial exposure of persons to lead in air appear consistent with this.