Mitsubishi Materials Corp.'s zinc and rare metal refinery in the city of Akita said Saturday it has detected unusually large amounts of toxic substances in groundwater within its premises.
No damage to human health has been reported, according to the company, which said the groundwater has not been used as potable water.
A survey conducted by a research firm found up to 18 milligrams of cadmium per liter in groundwater at 29 of 38 test locations, a level equivalent to 1,800 times greater than the maximum allowable amount under environmental conservation rules, the company said.
Mitsubishi Materials said it was notified of the results July 13 but did not report them to the city or prefecture until Tuesday. The city notified people living near the refinery Friday.
The city's health office blamed the company for the tardy response, saying the information should have been made public immediately.