It's hard to have a purely fact-based discussion about Japan's Fukushima water release plan.
Due to several scandals and a lack of transparency, trust appears to be low in both TEPCO, the company that operated the now-defunct Fukushima-Daiichi nuclear power plant, and the Japanese government, with its close ties to the atomic energy industry.
But the level of awareness about what's actually in the water is just as low.
Here's an overview of the facts.
Fukushima: Why is the water being released into the Pacific Ocean?
Storage tanks holding the cooling water at the ruined facility are full.
Japan has had to cool the reactors at the nuclear power plant since they were destroyed during a catastrophic tsunami in 2011. It takes 170 tons of cooling water per day to keep them cool.
In addition, rain and groundwater have been seeping into the site.
There are 1,046 storage tanks holding 1,343 million cubic meters of water.
Once the water has been filtered, it is considered safe and sent through a one-kilometer (0.62 mile)-long tunnel before being released into the Pacific Ocean — a process that will take an estimated 30 years to complete. The radioactive waste, meanwhile, will remain on land.
Is Japan allowed to release filtered cooling water into the sea?
Both Japan's atomic agency and the International Atomic Energy Agency (IAEA) have approved the plan. The IAEA said Japan had met international safety standards and that "discharges of the treated water would have a negligible radiological impact to people and the environment."
They said it had been common practice for nuclear power plants worldwide to release used cooling water into the ocean for decades routinely.
However, environmental and fishing experts, as well as neighboring states, have accused Japan of downplaying the level of radiation in the cooling water. They are concerned about far-reaching ocean contamination, potential environmental damage, a fall in fishing revenue and loss of reputation.
How will the water be prepared before it's released?
Before it's released into the ocean, the contaminated cooling water and groundwater will be sent through a filter system called the Advanced Liquid Processing System (ALPS).
ALPS can filter 62 different radionuclides — radioactive elements — but can't filter out the radioactive isotope tritium.
So, TEPCO wants to dilute the water until the concentration of tritium is reduced to about 1,500 Becquerel per liter or less than a fortieth of the national safety standard.
A becquerel (Bq) is a unit that measures the rate at which radioactive material emits radiation or how many atoms in the material decay in a given time.
TEPCO says that if the levels of tritium remain too high after filtration, they will repeat the process before releasing the water.
How dangerous is tritium?
Tritium is a form of hydrogen that occurs naturally in Earth's atmosphere. It is radioactive but far less dangerous than cesium-137 or strontium-90 — both of which are life-threatening.
It emits a weak beta particle that can be stopped by a sheet of plastic or human skin.
That's one reason Georg Steinhauser, a radioecologist at the Vienna University of Technology with expertise in the situation at Fukushima, has said that releasing the filtered water into the ocean is the best solution.
Steinhauser collected samples from the ruined Fukushima-Daiichi nuclear power plant site in 2013 and was a guest professor at Fukushima University a year later.
"If anyone's worried about tritium, they're uninformed. Tritium is not dangerous, neither for people nor the environment, if it's slowly released in diluted form," said Steinhauser. "It's a fraction of what is still in the ocean after the nuclear bomb tests. And very soon, it will be diluted to a point at which it is undetectable. So, there's no need for anyone to be scared."
Burkhard Heuel-Fabianek, who heads the radiation protection department at Germany's Forschungszentrum Jülich, has told DW that Japan's water release plan was "radiological sound."
Even if tritium gets into the body, the risks are low, said Heuel-Fabianek: "Since tritium is basically part of the water, the body sheds it relatively quickly. So, it lacks the biological effects that other elements have."
It's a different story if strontium-90 gets into the human body: "Strontium is absorbed by the bones, and once it's in the crystalline structure of the bones, you can't get rid of it again," he said.
How the Pacific Ocean acts as a massive dilutant
"There's an old English saying that 'the solution to pollution is dilution,' but people don't want to believe it," said Steinhauser. "If you dilute something to a point at which it's no longer dangerous, it is safe."
And once it's safe for humans, it's also safe for the environment, said Steinhauser. "Tritium does not accumulate — it's not like mercury in tuna. Tritium is a radioactive hydrogen in the form of a water molecule," he added. "It doesn't accumulate algae or plankton, it just gets diluted, more and more and more."
Is tritium a distraction tactic?
The environmental group Greenpeace has accused the Japanese government and TEPCO of distracting attention from the radiation levels in the water by focusing on tritium — other radionuclides will remain in the water even after it's been filtered.
"The Japanese government has done a very good job of focusing the attention of the media and the domestic audience on the tritium in the water and claiming that it poses no danger to the environment," said Shaun Burnie, senior nuclear specialist for Greenpeace.
"The contaminated water contains many radionuclides, which we know impact the environment and human health — including strontium-90," said Burnie.
Bernie told DW that leaked internal TEPCO documents show evidence that many radioactive elements, such as iodine, ruthenium, rhodium, antimony, tellurium, cobalt and strontium, will not be filtered to an undetectable level.
In addition, said Greenpeace, the ALPS is not designed to filter out the radioactive element carbon-14.
What are the alternatives for dealing with the Fukushima cooling water?
Environmental groups allege that the Japanese government and TEPCO have chosen the fastest and cheapest solution. They say there are alternatives, such as installing more storage tanks or allowing the cooling water to evaporate.
Steinhauser said using additional tanks would be a bad idea, especially because of the high risk of earthquakes in the region.
"If the tank were to leak and the cooling water got into the groundwater, the cooling water could spread in the aquifer (Ed.: An aquifer is a layer of rock that holds water) and dilute in a relatively small amount of water," said Steinhauser. "Releasing the cooling water into the ocean is the best and safest solution for the environment and humanity. Many have recommended this as the solution, including the International Atomic Energy Agency."
The other alternative idea of heating the tritium-contaminated cooling water and letting it evaporate is a known process. The safety threshold for tritium using that method is 5 Bq per liter.
However, many researchers consider the option problematic because the radioactive hydrogen released into the air is harder to control. The wind could carry the radioactive cloud to faraway places.
"I prefer the idea of releasing the water into the ocean to letting it evaporate," said Steinhauser. "Even if it's just small concentrations that get into the air I breathe and travel across the land, even if it's harmless, it is much safer to let it disappear in the ocean."
