A Chinese seafood company allegedly involved in exporting pesticide-tainted frozen mackerel to Japan, said yesterday it had never bought, stored or used the chemicals during processing.

The company added that the 18 samples, including raw materials and packages that it had selected for tests, were free of pesticide.

"We started investigations into the mackerel products immediately after we learned that a Japanese non-governmental testing organization had detected fatal pesticides in our exports," said Miao Qiang, president of Weihai Yuwang Aquatic Foods Co Ltd in Shandong Province.

Kouzai Bussan Co Ltd, a Japanese frozen food company, said on Monday that pesticide was detected in frozen mackerel processed in and imported from China.

While the residue standard of dichlorvos for fishery products is set at 0.01 parts per million (ppm) under Japan's food sanitation law, 0.14ppm of the pesticide was detected in the frozen mackerel processed in China, according to Japanese media.

The mackerel was imported from Denmark and all supplementary materials except salt were provided by the Japanese company, said the Chinese company.

"We were shocked by the news. But to protect consumers' health, our company has taken a series of preventive measures, including suspending the exports of relevant products," Miao said.

"But the allegedly tainted products were exported eight months ago. It takes time to find out what happened to them. We hope both sides will cooperate to solve the problem."

On February 8, without notifying the Japanese importer Shinko Zyorui Ltd and the Chinese processing company, Kouzai Bussan Co Ltd sent two bags of product samples to a local non-government testing organization for analysis for pesticide residue.

Test results showed that among the 295 tested items, only the residue of dichlorvos - an insecticide that can harm the human nervous system - failed to meet the Japanese standards.

On February 17, the Japanese frozen food company ordered a recall of the products on its Website and held a press conference on the issue the following day.

Miao said his company had been processing products in strict accordance with both Chinese and Japanese food sanitation standards. In fact, the Japanese company offered processing techniques for the exported frozen mackerel and sent supervisors to the Chinese firm during processing.