OSAKA -- Delicacy "matsutake" mushrooms imported from China earlier this month and subsequently found to contain agrochemical residue 28 times higher than the level allowed under the Food Sanitation Law have been put on the market, health ministry officials said Thursday.

Pesticide residue had earlier been found in frozen spinach from China, but this is the first case of Chinese-grown matsutake found to contain agrochemical residue, they said.

The finding has prompted the Health, Labor and Welfare Ministry to step up quarantine checks at the nation's 31 checkpoints.