L'Agence de protection de l'environnement des États-Unis reconnait que s'agissant des effets à long terme d'une exposition chronique à un niveau de radiation. L'augmentation du niveau d'exposition rend ses effets sur la santé plus susceptibles de se produire, mais n'ont aucune influence sur le type ou la gravité de l'effet.
En d'autres termes, elle reconnait explicitement qu'en ce qui concerne la dissimination de sources de radiations dans l'environnement [1], la fixation de seuils en deça desquels ces rejets n'auraient pas d'effet sur la santé est fallacieux (désigne ce qui est trompeur ou mensonger).
Source: Agence de protection de l'environnement des États-Unis
http://www.epa.gov/rpdweb00/understand/health_effects.html
What kinds of health effects does exposure to radiation cause?
In general, the amount and duration of radiation exposure affects the severity or type of health effect. There are two broad categories of health effects: stochastic and non-stochastic.
Stochastic Health Effects
Stochastic effects are associated with long-term, low-level (chronic) exposure to radiation. ("Stochastic" refers to the likelihood that something will happen.) Increased levels of exposure make these health effects more likely to occur, but do not influence the type or severity of the effect.
Cancer is considered by most people the primary health effect from radiation exposure. Simply put, cancer is the uncontrolled growth of cells. Ordinarily, natural processes control the rate at which cells grow and replace themselves. They also control the body's processes for repairing or replacing damaged tissue. Damage occurring at the cellular or molecular level, can disrupt the control processes, permitting the uncontrolled growth of cells--cancer. This is why ionizing radiation's ability to break chemical bonds in atoms and molecules makes it such a potent carcinogen.
Other stochastic effects also occur. Radiation can cause changes in DNA, the "blueprints" that ensure cell repair and replacement produces a perfect copy of the original cell. Changes in DNA are called mutations.
Sometimes the body fails to repair these mutations or even creates mutations during repair. The mutations can be teratogenic or genetic. Teratogenic mutations are caused by exposure of the fetus in the uterus and affect only the individual who was exposed. Genetic mutations are passed on to offspring.
Non-Stochastic Health Effects
Non-stochastic effects appear in cases of exposure to high levels of radiation, and become more severe as the exposure increases. Short-term, high-level exposure is referred to as 'acute' exposure.
Many non-cancerous health effects of radiation are non-stochastic. Unlike cancer, health effects from 'acute' exposure to radiation usually appear quickly. Acute health effects include burns and radiation sickness. Radiation sickness is also called 'radiation poisoning.' It can cause premature aging or even death. If the dose is fatal, death usually occurs within two months. The symptoms of radiation sickness include: nausea, weakness, hair loss, skin burns or diminished organ function.
Medical patients receiving radiation treatments often experience acute effects, because they are receiving relatively high "bursts" of radiation during treatment.
[1] Exemples:
Japan nuclear plant releases radioactive water into sea
Fukushima plant begins to discharge 11,500 tonnes of water into Pacific
Tokyo Electric estimates the potential additional annual dose to a member of the public would be approximately 0.6 millisieverts if they ate seaweed and seafood caught near the plant every day for a year. The annual permissible level for the general public in Japan is one millisievert.
Fukushima : Tepco colmate la fuite d'eau radioactive dans l'océan
Un premier "délestage" de 11 500 tonnes sur les 60 000 stockées sur le site est en cours et l'opération devrait se poursuivre jusqu'à vendredi 8 avril. Elle n'aura pas de conséquences sanitaires pour les populations, a assuré Hidehiko Nishiyama, le directeur adjoint de l'Agence du sûreté nucléaire et industrielle