Japan has expanded restrictions on tea shipments after detecting excessive levels of radioactive cesium in samples nearby Fukushima prefecture that was devastated by the March 11 quake and tsunami.

The health ministry asked the Chiba prefecture authority to expand a restriction on shipments of tea leaves produced Katsuura city in addition to six areas in the prefecture restricted on June 2.

Dried leaves from the Katsuura city, 78 kilometers (48 miles) from Tokyo, had radioactive cesium levels exceeding safety standards, the health ministry said in a statement issued yesterday. The leaves had 2,300 becquerels of cesium per kilogram, more than the government safety standard of 500 becquerels per kilogram, according to a statement on July 1 by the local government.

Japan has imposed shipment restrictions on tea from all areas in Ibaraki prefecture and some areas in Gunma, Tochigi and Kanagawa prefectures after the earthquake led to radiation leaks at a nuclear plant in Fukushima prefecture. Japan’s Nuclear Safety Commission on April 12 said an estimated 630,000 terabecquerels of radiation had been released into the atmosphere from the stricken Fukushima Dai-Ichi plant.

The country’s tea production, including fresh and dried leaves, was worth 102.1 billion yen ($1.3 billion) in 2009, according to the agriculture ministry.

Tea from Japan’s Shizuoka prefecture had above-standard radioactive cesium levels three months after radiation leaked from the plant about 360 kilometers from the area. Shizuoka, which accounts for about 40 percent of the nation’s tea output and lies southwest of Tokyo, asked farmers last month to recall products and halt shipments.

The dried leaves had 679 becquerels of cesium per kilogram, more than the 500 becquerels per kilogram safety government standard, the local government said on June 9. The contamination was found in leaves from the prefecture’s Warashina area, while tea produced in all 18 other areas had safe levels, based on tests conducted by tea farmers, according to the statement.