Perhaps the most consistently running theme that emerges in the interviews that the media have been conducting with Japanese citizens is that of distrust, particularly regarding conditions at the Fukushima Daiichi nuclear plant. This understandable, even if at least some of that distrust may have been induced by the ways in which the interviews were conducted. Japan is the first country to have experienced the impact of a nuclear catastrophe, and that is not the sort of thing to fade from collective memory.
The problem is that both the Japanese government and Tokyo Electric Power (TEPCO) have been trying to inform the public with simple statements. These tend to mask any underlying complexity and/or uncertainty. Consider the following lead sentences in an Al Jazeera English article based on wire sources:
Plutonium has been found in soil samples taken from the Fukushima Daiichi nuclear plant, operator Tokyo Electric Power said as efforts to bring the situation at the earthquake-stricken facility continue.
The samples were taken a week ago but the levels didn't pose a risk to human health, said Sakae Muto, TEPCO's vice-president.
Is Muto’s claim credible? This is one of those cases where there are not sufficient data to answer this question. Therefore, as a public service it seems worthwhile to reproduce the paragraphs provided by Wikipedia on plutonium toxicity:
Isotopes and compounds of plutonium are radioactive poisons that accumulate in bone marrow. Contamination by plutonium oxide (spontaneously oxidized plutonium) has resulted from a number of nuclear disasters and radioactive incidents including military nuclear accidents where nuclear weapons have burned. Studies of the effects of these smaller releases, as well as of the widespread radiation poisoning sickness and death following the Atomic bombings of Hiroshima and Nagasaki, have provided considerable information regarding the dangers, symptoms and prognosis of radioactive poisoning. PMID 19454804
During the decay of plutonium, three types of radiation are released-alpha, beta, and gamma. Alpha particles can travel only a short distance and cannot travel through human skin. Beta particles can penetrate human skin, but they cannot go all the way through the body. Gamma radiation can go all the way through the body. Alpha particles, beta particles, and gamma radiation all expose the body to ionizing radiation. Either acute or longer-term exposure carries a danger of unfavorable health outcomes including radiation sickness, cancer and death. The danger increases with the amount of exposure.
Though alpha radiation plutonium emits does not penetrate the skin it does irradiate internal organs when plutonium is inhaled or ingested. The skeleton, where plutonium is absorbed by the bone surface, and the liver, where it collects and becomes concentrated, are at risk. Plutonium is not absorbed into the body efficiently when ingested; only 0.04% of plutonium oxide is absorbed after ingestion. What plutonium is absorbed into the body is excreted very slowly, with a biological half-life of 200 years. Plutonium passes only slowly through cell membranes and intestinal boundaries, so absorption by ingestion and incorporation into bone structure proceeds very slowly.
Plutonium is more dangerous when inhaled than when ingested. The risk of lung cancer increases once the total dose equivalent of inhaled radiation exceeds 400 mSv. The U.S. Department of Energy estimates that the lifetime cancer risk for inhaling 5,000 plutonium particles, each about 3 microns wide, to be 1% over the background U.S. average. Ingestion or inhalation of large amounts may cause acute radiation poisoning and death; no human is known to have died because of inhaling or ingesting plutonium, and many people have measurable amounts of plutonium in their bodies.
The "hot particle" theory in which a particle of plutonium dust radiates a localized spot of lung tissue has been tested and found false – such particles are more mobile than originally thought and toxicity is not measurably increased due to particulate form.
However, when inhaled, plutonium can pass into the bloodstream. Once in the bloodstream, plutonium moves throughout the body and into the bones, liver, or other body organs. Plutonium that reaches body organs generally stays in the body for decades and continues to expose the surrounding tissue to radiation and thus may cause cancer.
Several populations of people who have been exposed to plutonium dust (e.g. people living down-wind of Nevada test sites, Hiroshima survivors, nuclear facility workers, and "terminally ill" patients injected with Pu in 1945–46 to study Pu metabolism) have been carefully followed and analyzed.
These studies generally do not show especially high plutonium toxicity or plutonium-induced cancer results. "There were about 25 workers from Los Alamos National Laboratory who inhaled a considerable amount of plutonium dust during the 1940's; according to the hot-particle theory, each of them has a 99.5% chance of being dead from lung cancer by now, but there has not been a single lung cancer among them."
In other words there is no good way to determine whether or not Muto’s claim is credible. At the very least that decision rests on the form of the plutonium that was detected. By all rights this information should have been included as part of the official response from TEPCO.