Findings on the
Toxicity of Plutonium

This paper is directed primarily to results of experiments in which laboratory animals were exposed once, briefly, by inhalation or intravenous injection, to an individual ... radionuclide.... The main long-term health effects were cancers....

Since the first production of plutonium in the 1940s, potential health effects from plutonium have been a concern for humans.

The few people exposed to plutonium and the relatively small intakes that have occurred, at least in the Western world, have resulted in very little direct information from human population studies.

• The Manhattan Project workers have been followed for decades, and few health effects have been observed.

• The situation is similar for the population of workers at the Rocky Flats facility.

• Some information is now being released from the former Soviet Union on selected worker populations who show biological effects, primarily pulmonary fibrosis and some increase in lung cancers.

Due to the lack of human data until very recently, animal studies were conducted to provide information of the metabolism and toxicity of plutonium.

Early studies showed that plutonium is poorly absorbed from the gastrointestinal tract and through the intact skin. From these data,

• inhalation or

• penetrating skin wounds

For this reason, studies were initiated at the Lovelace Respiratory Research Institute on the toxicity of inhaled plutonium. These studies were directed at several important health issues:

1. the toxicity of inhaled plutonium isotopes [in oxide form]
   ²³⁹PuO₂ [plutonium-239] and ²³⁸PuO₂ [plutonium-238];

2. the importance of the homogeneity of the
   distribution of dose within the lung;

3. interspecies comparison of the
   toxicity of inhaled plutonium;

4. the effect of age at the time of exposure.

At lower activity levels and at much longer times after inhalation, lung cancer was the primary effect observed, especially from ²³⁹PuO₂ [plutonium-239] ....

In these studies, the plutonium aerosols were delivered as monodisperse particles. That made it possible to alter the distribution of local dose within the lung using many small particles or a few large particles [of plutonium]. Similar risks of developing lung cancer were found in both cases....

Studies in multiple species -- primarily dogs, rats, and mice -- showed similar biological effects and cancer risks. This finding has provided increased confidence in the extrapolation of the animal data [for the purpose of] predicting health risks to people.

The studies on the effect of age at the time of exposure are still in analysis, but early indications are that old dogs may be more sensitive to plutonium dioxide than young adults and juveniles. The old dogs developed lung injury at lower doses and shorter time intervals than the younger dogs....

A list of the publications that have been completed is available.

See ''Publications of the ITRI
Nuclear Toxicology Program: 1960-1996''
ITRI-149, Inhalation Toxicology Research Institute,
Lovelace Respiratory Research Institute (Dec. 1996).

In summary, inhaled plutonium dioxide was shown to cause serious biological effects in a dose-related fashion in the organs that received the largest doses....

The uniformity of dose distribution in the lung did not affect the probability of developing a cancer, and the probability of developing lung cancer from inhaled ²³⁹PuO₂ [plutonium-239] was similar among several laboratory animal species. Age at exposure was important, and older animals were more sensitive for developing biological effects.

Based on the similar results obtained among laboratory animal studies, extrapolation of these results to humans appears to be reasonable.