The decision by the Japanese government to begin releasing 1.25 million tonnes of treated water from the Fukushima nuclear plant site over a 10 year period has caused a major stir not only amongst environmental NGO's but also regional countries with historic emnity to Japan.   
Greenpeace alleges that radionuclides released into the sea "may damage DNA of humans and other organisms." China states that "the release is extremely irresponsible and will pose serious harm to the health and sagety of people in neighbouring countries and the international community." 
So what are the politics and science behind the controversy?   
The Fukushima water has been treated and the almost all radio-isotopes have been removed except for tritium. Just how dangerous is it? Tritium is a weak beta emitter with 70x less energy then the the naturally occuring and ubiquitous intracellular radioisotope Potassium 40 which undergoes 4600 radioactive decays per second in our bodies.  
The health impacts of a radioisotope are multifactorial. The type of radiation emitted, the energy of that decay, the physical and biologic halflife of the isotope. The amount of tritium that one would need to drink to match a dose from something like a CT scan is simply impossible to ingest.  
In response to the Fukushima accident in an effort to gain the trust of the population Japan has already reset its regulatory limits for radiation in drinking water at 1/100th that of the EU. Are these efforts actually counter productive?  
Dr. Geraldine Thomas is a senior academic and Chair in Molecular Pathology at the Faculty of Medicine of Imperial College London. She is an active researcher in fields of tissue banking and molecular pathology of thyroid and breast cancer. She is also the director of the Chernobyl Tissue bank.