One month has passed since the operator of the Fukushima Daiichi nuclear plant began releasing treated and diluted water into the Pacific Ocean.

The first round of the release ended on September 11.

The nuclear plant suffered a triple meltdown in the 2011 earthquake and tsunami. Water used to cool molten fuel has been mixing with rain and groundwater that seeps into the damaged reactor buildings.

The accumulated water is being treated to remove most radioactive substances, but still contains tritium. The treated water is stored in more than 1,000 tanks.

Before releasing the treated water into the ocean, the plant's operator dilutes it to reduce tritium levels to about one-seventh of the World Health Organization's guidance level for drinking water.

The operator says it discharged 10 tanks or nearly 8,000 tons of treated water in the first round.

The storage tanks were 98 percent full before the release. But following the discharge, the amount of stored treated water decreased for the first time since the 2011 accident from 1.345 million tons to 1.338 million tons.

Ever since the start of the release, Tokyo Electric Power Company as well as central and local government officials have been testing seawater and fish samples from multiple points offshore from the plant.

As for the seawater, they say the concentration of tritium has been 10 becquerels per liter at the highest so far. This is far below 700 becquerels per liter, the level set by the utility for suspending the release. That means there has been only a negligible impact on the environment.

Analyses of fish samples also showed all below the detectable level of 10 becquerels.

The utility plans to carry out four rounds of the water discharge during the fiscal year that ends next March. A total of 31,200 tons of water will be released -- the equivalent of 40 full tanks.