Radioactivity & Environment
Plutonium and the Environment
Every now and then a shipment of plutonium circumnavigates the Cape. Environmental groups are usually concerned about the safety of the environment and the people.
The two most burning questions on everybody’s mind seems to be, what the chances are that plutonium can enter our waters in some way or another and what the environmental consequences would be if that happens.
Environmental groups, in the case of plutoniom, usually warn that no risk is acceptable. In the case of oil spills, some risk is accepted despite the massive, proven effects of oil spills on the ecosystem. As a result, public perception about the severity of the environmental impact of plutonium is that it is “the most dangerous substance on earth.”
In the questions below, we try to inform you of the most recent scientific facts about plutonium and its potential impact on the environment. We also add practical examples and our experience gained from it.
What is Plutonium?
Plutonium is a chemical element that exists in trace quantities in natural uranium ores. Fifteen isotopes (nuclear variants) of plutonium are known. Plutonium is radioactive and decays mostly through emission of rays of alpha particles. Plutonium is also produced from uranium in nuclear reactors and is therefor one of the products of nuclear power generation.
Plutonium readily undergoes nuclear fission (a type of reaction that releases huge amounts of energy) when bombarded with neutrons (sub-nuclear particles) in the right way. This property makes it a substance used as an explosive ingredient in nuclear weapons. Usually however plutonium is of concern because of its radiological toxicity.
In the form of its metal plutonium has a silvery appearance and takes on a yellow tarnish when slightly oxidised. A relatively large piece of plutonium metal is warm to the touch because of the energy given of by alpha decay. Larger pieces will produce enough heat to boil water. This curious property coupled to the knowledge that it can be used in nuclear weapons gives a "creepy" appeal to the metal and may have contributed to the myths surrounding it.
Most Toxic Substance?
Plutonium has acquired the false reputation of being the most toxic substance known to humankind.
The fact is that only certain forms of plutonium administered via certain routes are toxic. Even then there are other radioisotopes and chemical substances that are much more toxic than plutonium.
It is also comforting to learn that more is known about the toxicity of plutonium than about most other hazardous substances.
Origin of the Myth
Like most myths it is hard to pinpoint the exact origin. An important contributing factor may have been a report by Tamplin and Cochran in February 1974. They proposed a "hot particle" theory according to which plutonium lodges in concentrated aggregates in sensitive areas of the lungs where it produces cancer more effectively.
As a result they estimated plutonium to be 115 000 times more poisonous than official figures. One year later Tamplin reduced their estimate by a factor of hundred. To date no supporting evidence for the original theory has been forthcoming.
Indeed, experimental evidence points to the exact contrary of the hot particle theory. Despite this the media still refer to the original figures derived from the unsubstantiated theory.
Whatever the origin, the myth spread quickly because news about a particularly potent poison seems to fascinate people. For the same reasons some people have turned even innocent little spiders like the Daddy Longlegs into potential monsters.
Is Plutonium Toxic?
Plutonium is toxic on two accounts but is far from being the most toxic substance known to humankind. As a heavy metal it has a chemical toxicity. However, its chemical toxicity is much lower than its radiological toxicity.
The rays of alpha particles produced by plutonium have a range of only about 40 millionth of a metre in tissue. Therefore if plutonium is deposited on the surface of the skin the alpha particles will not even penetrate the outer layers of the epithelium (major skin tissue).
So, if plutonium contamination is restricted to the skin it can simply be cleaned off without much radiological hazard. One isotope of plutonium emits beta radiation and may represent a certain amount of skin hazard.
The picture is different if plutonium finds its way into the body. It then comes in contact with soft living tissue and may cause cancer as a result of alpha bombardment of the tissue. Even then formation of cancer is a stochastic (probabilistic) process and not a certainty.
For instance if a large number of people ingest plutonium to the same extent, only a certain percentage of them will develop cancer and only a percentage of those will die as a result. Obviously these deaths are not instantaneous, and cancerous tumours will only be observed after a latency period of 5 -25 years.
The radiological toxicity of plutonium is highest when particles are inhaled into the lungs. Absorption of plutonium administered orally is less than 0.1 percent. Once plutonium is absorbed into the body it deposits in the bone, bone marrow and liver.
When plutonium is inhaled into the lungs in fine particle or aerosol form it has the worst effect. In this form a lethal dose is approximately 0,23 mg.
To achieve a realistic assessment of the toxicity of plutonium it simply has to be compared quantitatively with other toxins.
The maximum density of plutonium is about 20 gram per ml. So, one teaspoon of plutonium amounts to about 100 grams. The specific activity of plutonium is about 61400 micro-curies per gram.
Let us now assume that the permissible level of 0.04 micro-curies per person is exceeded by a factor 10 so that the chance for some toxic effects is reasonably high, then only 0.4 micro-curies per person is allowed.Therefore about 153 500 people can all receive a ten times normal dose from one gram of plutonium.
This is with the assumption that the body absorbs all the plutonium, which is very far from the truth! Under these very special circumstances about 15 million people could be harmed (most certainly not killed) by one teaspoon full of plutonium.
However, no mechanism is known to science that allows plutonium to direct itself towards the mouths of 15 million carefully lined up individuals. It spreads out into the environment in quasi-random manner.
The dilution factor is huge. After dilution some of the plutonium might be ingested through the food chain or through inhalation. To claim that one-teaspoon full of plutonium is likely to kill 15 million people harbours the same amount of logic as the statement that a swimming pool is likely to kill thousands of people! Assuming that each person's head is forced under water one by one the latter can also be proven quite readily.
How Toxic is Plutonium?
We already know that the toxicity of plutonium is due to its radioactivity and that it should be expressed in terms of probability of contracting cancer. Immediate death due to plutonium can only occur when if approximately 0,23 mg is inhaled directly into the lungs as a finely divided powder.
Plutonium is also not easily absorbed through the skin. Various solutions of plutonium applied to unbroken skin leads to absorption of between 0.002 and 0.25 percent. Absorption through the skin normally only occurs when the skin is damaged. Entry of plutonium through wounds occurred in various occupational accidents, so that the effects are relatively well known. Although a fibrous nodule can form at the wound in some instances, no cases of cancerous growth have been reported to date.
All these facts and figures might have you a bit confused.Is plutonium dangerous or not and how do we take dilution factors and realistic plutonium uptake into account?
Let us look at the following real-life example. A news article was published about this case in the New Scientist of 27 June 1998.
”The island Mururoa in the South Pacific will be polluted with plutonium for centuries. This is the result of thirty years of French nuclear testing. Between 1966 and 1996 the French set off 193 nuclear test explosions at the Mururoa and Fangataufa atolls. Of these 46 were above ground and 147 below. This contaminated lagoons and left plutonium scattered over atolls. Recently the International Atomic Energy Agency co-ordinated an extensive scientific study of the end result of this testing. Fifty-five scientists from 18 countries worked together to produce a 2000-page study. The study revealed that plutonium particles are scattered all over Mururoa islets of Colette, Ariel and Vesta and that several kilograms of plutonium are spread through the sediments of the lagoons. Despite this the study concludes that the contamination will not harm people's health and is unlikely to damage the natural environment. The studies are not based on speculation or even calculation, but on actual measurements of the real radiation risk at Mururoa.”
A separate study by the international atomic energy agency on Bikini atoll, where the US tested nuclear weapons, recommends that the 160 residents and their families who want to return should only do so if they eat imported food. The US government in 1946 evacuated these islanders so that they could use the atoll for 23 above-the-ground nuclear tests.
Scientists say that anyone who wants to return to Bikini atoll should avoid homegrown food and remove contaminated soil from around their dwellings. Although the latter sounds serious, it certainly does not appear as if living on Bikini atoll is deemed life threatening by the scientists. It must further be remembered that a comfortable safety margin will already be allowed for if the study recommends conditional return to the atoll.
Here we have cases of areas contaminated by real nuclear explosions spreading kilograms of plutonium over relatively small areas of land and water. The natural dilution of the plutonium contamination resulted in radiation hazard at any one position far less than the gloomy predictions of plutonium paranoids.
The Necsa Viewpoint
Despite the fact that plutonium it is not even remotely as toxic as claimed by anti-nuclear activists we still believe that:
- Plutonium, because of its radiological toxicity and long half-life remains a radiological pollutant that should be handled with great responsibility.
- Precautions must be taken to minimise the risk of plutonium contamination of the biosphere.