Lu Yueting, 39, admitted at his trial at Shijiazhuang Intermediate People's Court that he injected methamidophos, a type of insecticide, five times into frozen dumplings while working as a cook at Tianyang food plant in Hebei province in 2008.
The dumplings were later sold in Japan and Chengde city in China's Hebei province.
The contaminated food made a five-year-old Japanese child "seriously ill" from food poisoning and another 12 people in China and Japan suffered minor illness, according to prosecutors.
Tianyang food plant was forced to shut down, products recalled, with a direct economic loss of at least 5.5 million yuan (USD 897,000).
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A total of 1,300 workers lost their jobs.
Prosecutors said Lu's behaviour caused serious consequences and he should be punished strictly.
Lu, while admitting to the crime, argued he injected the pesticides not to "intentionally harm others" but to "arouse the manager's attention and then take the chance to ask for a pay raise", state-run Xinhua news agency reported today.
He said the salary and welfare of a contracted worker at Tianyang differs a lot from a temporary worker.
"I was given 100 yuan as a Spring Festival bonus in 2007, while other contracted workers received thousands of yuan. I waited and waited. I thought I had worked for the company for so long and deserved more incentives. I hoped the manager could pay attention to people like me," he said.
After having injected the toxic substances, Lu said he wrote three anonymous report letters to notify the company's manager that the food had been contaminated, but the manager didn't take any action.