Abstract The possible use of radioactivity dispersal de- vices by terrorist groups has been recently reported in the news. In this paper, we discuss the threat of terrorist attacks by plutonium, with particular attention to the dis- persal of plutonium by explosion or fire. Doses resulting from inhalation of radioactive aerosol induced by a plu- tonium explosion or fire are simulated using a Gaussian plume model (the HOTSPOT code) for different meteo- rological conditions. Ground contamination and resus- pension of dust are also considered in the simulations. Our simulations suggest that acute effects from a pluto- nium dispersal attack are very unlikely. For late stochas- tic effects, the explosion poses a greater hazard than fire. However, even in the worst-case scenario, the dispersed plutonium would cause relatively few excess cancers (around 80 in a city of 2 million inhabitants) after many years from the explosion, and these excess cancers would remain undetected against the background of can- cer fatalities. Introduction The recent tragic terrorist attacks in New York and Washington on September 11, 2001 have caused an in- creased concern for the possible use of non-conventional weapons (nuclear, biological, and chemical warfare) in future attacks on metropolitan areas. Warnings about the use of nuclear weapons by terrorists have been given for many years [1, 2], but the potential for such use is cur- rently the cause of particular anxiety. Although smuggled weapons-grade radioactive mate- rial might be used to make nuclear bombs, engineering a radioactive release is easier. There is substantial evi- dence that terrorist groups have access to nuclear materi- al that could be used for nuclear detonations. However, large amounts of 235 U or 239 Pu are necessary to prepare a nuclear bomb. On the other hand, a limited amount of 239 Pu could be sufficient for an attack on a large city, by three possible actions: a. Water contamination by introducing plutonium into the municipal water supply b. Use of a radioactivity dispersal device (RDD) or “dirty bomb”, where conventional explosive is wrapped in a shroud of plutonium that creates fallout when the bomb explodes c. Ignition of plutonium thereby causing a plume of radioactive material. Plutonium would be the preferred choice for terrorist attacks, because of its high activity (about 3 kBq/μg) and its well known radiological toxicity by inhalation [3, 4]. In addition, public perception of the plutonium risk is grossly exaggerated, which would certainly lead to wide- spread panic in the event of an attack. Dispersal of plutonium into the water supply of a large city would probably cause very limited damage. As a matter of fact, plutonium is much less of a hazard in water than in air, because only about 0.001% of the material released in water would be dissolved and sus- pended [5], the rest being immobilized in sediments. Plutonium in solution would be greatly diluted by the large volume of the water reservoir of a large city, and uptake by the gastrointestinal tract is minimal. The com- mitted effective dose from ingestion of plutonium (239 plus 240 isotopes) is around 0.04 mSv/μg, to be com- pared to 250 mSv/μg by inhalation [6]. Based on these calculations, Sutcliffe et al. [7] excluded any serious health consequences of plutonium contamination in municipal water supplies. However, explosions and fires pose a greater threat. Particles smaller than about 3 μm in activity median aerodynamic diameter (AMAD) will become airborne and can be inhaled. Such an aerosol will deposit in the lungs, and migrate via the blood stream to selectively concentrate in the bones and the liver. Acute effects such as pulmonary edema are possible at high doses, whereas M. Durante ( ✉ ) · L. Manti Dipartimento di Scienze Fisiche, Università “Federico II”, Monte S. Angelo, Via Cintia, 80126, Napoli, Italy e-mail: durante@na.infn.it Tel.: +39-081-676440, Fax: +39-081-676346 Radiat Environ Biophys (2002) 41:125–130 DOI 10.1007/s00411-002-0156-5 ORIGINAL PAPER Marco Durante · Lorenzo Manti Estimates of radiological risk from a terrorist attack using plutonium Received: 21 January 2002 / Accepted: 19 April 2002 / Published online: 29 May 2002 © Springer-Verlag 2002