China began checking ballast water loaded on cargo ships arriving from Japan at some key ports, likely for radiation level inspections, at roughly the same time the neighboring country began releasing treated radioactive water from the crippled Fukushima nuclear plant, trade sources said Thursday.

The monitoring of ballast water -- seawater used to provide stability and maneuverability during a voyage -- began as Beijing voiced its strong opposition to Japan's release of the treated water into the Pacific Ocean, which commenced on Aug. 24. China also suspended all seafood imports from Japan due to safety concerns.

Even before the water discharge began, Beijing had already tightened controls on marine product imports from Japan in July by introducing blanket radiation testing.

Photo taken in August 2023 shows Qingdao Port in China's Shandong Province. (VCG/Getty/Kyodo)

According to the sources, the examination of ballast water samples taken from Japanese territorial seas has been happening since July at ports in Tianjin, as well as Shandong Province in eastern China.

Ballast water is usually discharged from ships when cargo is carried onto them. Local authorities in China have notified operators that they will ban them from releasing ballast water at Chinese ports if the radiation levels in their samples exceed a certain limit, but so far no such instances have been reported, the sources said.

China has yet to publicly announce the ballast water inspections and no official documents or notifications about them have been released. There have been no reports of major disruptions to trade processing or cargo transportation due to the checks and the Japanese government is gathering relevant information, the sources said.

China apparently intends to continue conducting checks independently, given that, according to sources familiar with the bilateral relationship, it has rejected Japan's proposal that it join an international framework for independently assessing the results of radiation level monitoring of the treated water.

China calls the water "nuclear-contaminated" and demands that Japan immediately halt the discharge. The International Atomic Energy Agency concluded in a report in July that the Fukushima water release plan aligns with global safety standards and will have a "negligible" impact on people and the environment.

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