A method for investigating the metabolism of the transportable fraction of plutonium aerosols.

The metabolism of the transportable fraction of both 'soluble' and 'insoluble' forms of plutonium following their deposition in the respiratory system of the rat by either inhalation or pulmonary intubation has been investigated. The results have shown that the transportable fraction varied considerably with the chemical form of the plutonium. Thus at one week after the pulmonary intubation of a solution of plutonium citrate, the extrapulmonary tissue deposit was 69% of the initial pulmonary deposit whilst in the case of a suspension of plutonium dioxide the corresponding value was only 0.075%. However, the metalbolism of plutonium following its entry into the systemic circulation was largely independent of the original chemical form deposited in the lung. The liver accumulated only about 16% of the activity deposited in tissues from the blood, implying that plutonium was circulating in the blood predominantly in a momomeric form. The cumulative excretion of plutonium in the urine over the first week after pulmonary deposition as either the dioxide, citrate or nitrate was equivalent to about 4.5% of the extrapulmonary tissue deposit and the results suggest that this value could be used as a basis for calculating the activity deposited in tissue from the blood in man. This study also demonstrated that mixed aerosols of plutonium dioxide and sodium oxide are more transportable in the lung than aerosols of plutonium dioxide alone. A maximum transportability was reached at a Pu : Na atomic ratio of about 1:20, when the transportable fraction of plutonium was forty-five times that from a plutonium dioxide aerosol alone.