The mass poisoning has been traced to Maruha Nichiro Holdings, which is recalling about 6.4 million bags of frozen foods, including croquettes, frozen pizza and chicken nuggets, after 2.6 million times the permitted levels of pesticide were found in the products.
While 1.2 million packages have been recovered, another 5.2 million are still unaccounted for.
Police are now investigating the company’s plant in eastern Japan, and Japanese media report that police suspect the malathion was mixed into products there.
“We test products several times a day for evidence of spoilage, based on the law, but we had no reason to believe pesticides would be present, so we didn’t test for that,” Ichiro Gohara, a spokesman for the company told Bloomberg News.
Symptoms of the poisoning include vomiting and diarrhea, and customers complained of a strong odor from the foods. According to Maruha Nichiro, none of the contaminated products has been shipped to other countries.
Malathion is registered with the U.S. Environmental Protection Agency for use on crops and is also an ingredient in head lice treatments.