Radioactive substances have been left unremoved from treated but still tritium-containing water at the crippled Fukushima Daiichi nuclear power plant, Kyodo News learned Sunday.

The government and Tokyo Electric Power Company Holdings Inc. have faced the pressing need of disposing of such treated water now kept in tanks. One option is to dump it into the sea, as tritium is said to pose little risk to human health.

If the plan goes through, tritium-tainted water from the nuclear plant is expected to be diluted so it will likely lower the levels of other radioactive materials as well before being discharged.

But local fishermen and residents have expressed worry about the water discharge and a government panel debating how to deal with the water has mainly focused on tritium, not other radioactive substances.

According to Tepco, a maximum 62.2 becquerels per liter of lodine 129, far higher than the 9 becquerel legal limit, was found in the water filtered by the Advanced Liquid Processing System used to remove various types of radioactive materials.

Lodine 129 has a half-life of 15.70 million years.

Tepco, which gathered data in fiscal 2017 through March, also detected a maximum 92.5 becquerels of Ruthenium 106, shy of the 100 becquerel legal limit, as well as 59 becquerels of technetium 99 against the limit of 1,000 becquerels.

The Fukushima Daiichi nuclear complex was damaged by the 2011 earthquake and tsunami. The Nos. 1 to 3 reactors suffered fuel meltdowns as their cooling systems were crippled.

Water has been injected to keep the fuel cold but it is extremely toxic. The water is filtered but it is hard for tritium to be separated.

As of August, around 920,000 tons of tritium-containing water are stored in some 680 tanks within the premises of the plant. But Tepco said it has not checked the concentration of radioactive materials in each tank.

The government has examined multiple options to dispose of tritium-containing water, including the release of it into the sea, the atmosphere and into geographical layers.

Toyoshi Fuketa, who heads the Nuclear Regulation Authority, has been calling for discharging the water into the sea as the "only" solution.