Since the mid-20th century,plutonium in the environment has been primarily produced by human activity. The first plants to produceplutonium for use inCold Waratomic bombs were theHanford nuclear site in Washington, and theMayak nuclear plant, inChelyabinsk Oblast,Russia. Over a period of four decades,[1] "both released more than 200 millioncuries ofradioactive isotopes into the surrounding environment – twice the amount expelled in theChernobyl disaster in each instance."[2]
The majority ofplutoniumisotopes are not short-lived on ageological timescale,[3] though it has been argued that traces of the long-lived244Pu isotope still exist in nature.[4] This isotope has been found inlunar soil,[5]meteorites,[6] and in theOklo natural reactor.[7] However, one study on plutonium inmarinesediments indicates that the atomic bomb fallout accounts for 66% of the239Pu and 59%240Pu in theEnglish Channel. In contrast,nuclear reprocessing contributes the majority of the238Pu and241Pu in the Earth's oceans, whereas nuclear weapons testing is responsible for only 6.5% and 16.5% of these isotopes, respectively.[8]
Richland, Washington was the first city established to support plutonium production at the nearbyHanford nuclear site, to power the American nuclear weapons arsenals.Ozersk, Russia supported plutonium production to power the Soviet nuclear arsenals at theMayak nuclear plant. These were the first two cities in the world to produce plutonium for use incold waratomic bombs.[2]
In the 2013 book,Plutopia: Nuclear Families, Atomic Cities, and the Great Soviet and American Plutonium Disasters,Kate Brown explores the health of affected citizens in both the United States and Russia, and the "slow-motion disasters" that still threaten the environments where the plants are located.[1] According to Brown, the plants atHanford andMayak released over 200 millioncuries of radioactive isotopes into the surrounding environment over four decades, which is twice the amount expelled in theChernobyl disaster in each instance.[2]
Most of theradioactive contamination over the years from Hanford and Mayak were part of normal operations. Unforeseen accidents did occur, but plant management kept this secret, and the pollution continued unabated. Even today, as pollution threats to health and the environment persist, the government conceals information about the associated risks from the public.[2]
About 3.5 tons of plutonium have been released into the environment by atomic bomb tests. While this might sound significant, it has only resulted in a very small dose to the majority of the humans on Earth. Overall the health effects offission products are far greater than the effects of theactinides released by a nuclear bomb detonation. The plutonium from the fuel of the bomb is converted into a high-firedoxide that is carried high into the air. It slowly falls to earth as globalfallout and is notsoluble, and as a result it is difficult for this plutonium to be incorporated into an organism if ingested. Much of this plutonium is absorbed into sediments of lakes, rivers and oceans. However, about 66% of the plutonium from a bomb explosion is formed by the neutron capture of238U; this plutonium is not converted by the bomb into a high firedoxide, as it is formed more slowly. This formed plutonium is more soluble and more harmful asfallout.[9]
Some plutonium can be deposited close to the point of detonation. The glassytrinitite formed by theTrinity bomb has been examined to determine what actinides and otherradioisotopes it contained. A 2006 paper[10] reports the levels of long lived radioisotopes in the trinitite.152Eu and154Eu was mainly formed by the neutron activation of theeuropium in the soil, and the level of radioactivity for these isotopes is highest where the neutron dose to thesoil was larger. Some of the60Co was generated by activation of thecobalt in the soil, but some was also generated by the activation of the cobalt in thesteel (100 foot) tower on which the bomb stood. This60Co from the tower would have been scattered over the site reducing the difference in the soil levels.133Ba and241Am were created by the neutron activation of barium and plutonium inside the bomb. Thebarium was present in the form of thenitrate in the chemical explosives used while the plutonium was thefissile fuel used.
As the239Pu/240Pu ratio only changed slightly during the Trinity detonation, it has been commented[11] that this isotope ratio for the majority of atomic bombs (in Japan the239Pu/240Pu ratio in soil is normally in the range 0.17 to 0.19[12]) is very different than from the bomb dropped uponNagasaki.
Plutonium has also been released into the environment insafety trials. In these experiments,nuclear bombs have been subjected to simulated accidents or detonated with an abnormal initiation of their chemical explosives. An abnormal implosion will result in a compression of theplutonium pit, which is less uniform and smaller than the designed compression in the device. In these experiments where no or very littlenuclear fission occurs, plutonium metal has been scattered around the test sites. While some of these tests have been done underground, other such tests were conducted in open air. A paper on theradioisotopes left on an island by theFrench nuclear bombs tests of the 20th century has been printed by theInternational Atomic Energy Agency and a section of this report deals with plutonium contamination resulting from such tests.[13]
Other related trials were conducted atMaralinga, South Australia where both normal bomb detonations and "safety trials" have been conducted. While the activity from the fission products has decayed away almost totally (as of 2006) the plutonium remains active.[14][15]
Plutonium can also be introduced into the environment via the reentry of artificial satellites containingatomic batteries. There have been several such incidents, the most prominent being theApollo 13 mission. TheApollo Lunar Surface Experiments Package carried on theLunar Module re-entered the atmosphere over the South Pacific. Many atomic batteries have been of theRadioisotope thermoelectric generator (RTG) type. The Plutonium-238 used in RTGs has ahalf-life of 88 years, as opposed to the plutonium-239 used innuclear weapons andreactors, which has ahalf-life of 24,100 years.[full citation needed] In April 1964 aSNAP-9A failed to achieve orbit and disintegrated, dispersing roughly 1 kilogram (2.2 lb) ofplutonium-238 over all continents. Most plutonium fell in the southern hemisphere. An estimated 6300 GBq or 2100man-Sv of radiation was released[16][17][18][19] and led to NASA's development of solar photovoltaic energy technology.[20][better source needed]
Chain reactions do not occur inside RTGs, so anuclear meltdown is impossible. In fact, some RTGs are designed so that fission does not occur at all; rather, forms ofradioactive decay which cannot trigger other radioactive decays are used instead. As a result, the fuel in an RTG is consumed much more slowly and much less power is produced. RTGs are still a potential source ofradioactive contamination: if the container holding the fuel leaks, the radioactive material will contaminate the environment. The main concern is that if an accident were to occur during launch or a subsequent passage of a spacecraft close to Earth, harmful material could be released into the atmosphere. However, this event is extremely unlikely with current RTG cask designs.[full citation needed]
In order to decrease the risk of the radioactive material being released, the fuel is typically stored in individual modular units with their own heat shielding. They are surrounded by a layer ofiridium metal and encased in high-strengthgraphite blocks. These two materials are corrosion and heat-resistant. Surrounding the graphite blocks is an aeroshell, designed to protect the entire assembly against the heat of reentering the Earth's atmosphere. The plutonium fuel is also stored in a ceramic form that is heat-resistant, decreasing the risk of vaporization and aerosolization. The ceramic is also highlyinsoluble.[full citation needed]
The US Department of Energy has conducted seawater tests and determined that the graphite casing, which was designed to withstand reentry, is stable and no release of plutonium should occur. Subsequent investigations have found no increase in the natural background radiation in the area. The 1970Apollo 13 crisis represents an extreme scenario due to the highre-entry velocities of the craft returning from cislunar space. This accident has served to validate the design of later-generation RTGs as highly safe.
Plutonium has been released into the environment in aqueous solution fromnuclear reprocessing anduranium enrichment plants. The chemistry of this plutonium is different from that of the metal oxides formed fromnuclear bomb detonations.
One example of a site where plutonium entered the soil isRocky Flats where in the recent pastXANES (X-rayspectroscopy) has been used to determine the chemical nature of the plutonium in thesoil.[21] The XANES was used to determine theoxidation state of the plutonium, whileEXAFS was used to investigate the structure of the plutonium compound present in the soil andconcrete.[22]
Because plutonium oxide is involatile, most of the plutonium in the reactor was not released during the fire. However that which was released can be measured. V.I. Yoschenko et al. reported that grass and forest fires can make thecaesium,strontium andplutonium become mobile in the air again.[23]
The ongoing crisis at this site includes Spent Fuel Pools on the upper floors, exposed to the elements with complex MOX and plutonium products. The Japanese Government Taskforce has asked for submissions to the International Research Institute for Nuclear Decommissioning[24] in regards to the ongoing Contaminated Water Issues.[25]
There have been 18 incidents concerning theft or loss ofhighly enriched uranium (HEU) andplutonium confirmed by theIAEA.[26]
One case exists of aGerman man who attempted to poison his ex-wife with plutonium stolen from WAK (WiederaufbereitungsanlageKarlsruhe), a small scale reprocessing plant where he worked. He did not steal a large amount of plutonium, just rags used for wiping surfaces and a small amount of liquid waste. The man was sent toprison for his crime.[27] At least two other people were contaminated by the plutonium.[citation needed] Two flats inRhineland-Palatinate were also contaminated.[28] These were later cleaned at a cost of two millioneuros.
Plutonium, like other actinides, readily forms a dioxideplutonyl core (PuO2). In the environment, this plutonyl core readily complexes with carbonate as well as other oxygenmoieties (OH−, NO2−, NO3−, and SO42−) to form charged complexes which can be readily mobile with low affinities to soil.[citation needed]
PuO2 formed from neutralizing highly acidic nitric acid solutions tends to form polymeric PuO2 which is resistant to complexation. Plutonium also readily shifts valences between the +3, +4, +5 and +6 states. It is common for some fraction of plutonium in solution to exist in all of these states in equilibrium.[citation needed]
Plutonium is known to bind to soil particles very strongly (see above for an X-ray spectroscopic study of plutonium in soil andconcrete). Whilecaesium has very different chemistry to the actinides, it is well known that both caesium and many of the actinides bind strongly to theminerals in soil. Hence it has been possible to use134Cs labeled soil to study the migration of Pu and Cs in soils. It has been shown thatcolloidal transport processes control the migration of Cs (and will control the migration of Pu) in the soil at theWaste Isolation Pilot Plant according to R.D. Whicker and S.A. Ibrahim.[29] J.D. Chaplin et al. recently reported advances in theDiffusive gradients in thin films technique, which have provided a method to measure labile bioavailablePlutonium in soils, as well as in freshwater and seawater.[30]
Mary Neu (atLos Alamos in the USA) has done some work which suggests thatbacteria can accumulate plutonium because theiron transport systems used by the bacteria also function as plutonium transport systems.[31][32][33]
Plutonium ingested by or injected into humans is transported in thetransferrin basediron(III) transport system and then is stored in theliver in the iron store (ferritin), after an exposure to plutonium it is important to rapidly inject the subject with achelating agent such ascalcium complex[34] ofDTPA.[35][36] This antidote is useful for a single exposure such as that which would occur if aglove box worker were to cut his or her hand with a plutonium-contaminated object. The calcium complex has faster metal binding kinetics than thezinc complex but if the calcium complex is used for a long time it tends to remove important minerals from the person. The zinc complex is less able to cause these effects.
Plutonium that is inhaled by humans lodges in the lungs and is slowly translocated to thelymph nodes. Inhaled plutonium has been shown to lead to lung cancer in experimental animals.[37]
