Large quantities of insecticide residue have been found on frozen spinach from China used in prepared meals sold at Lawson Inc. convenience stores, the Tokyo Metropolitan Government announced Wednesday.

In about 20 tons of spinach sold to Lawson, the metropolitan government found levels the insecticide chlorpyrifos that were 14 times higher than permitted by the Food Sanitation Law.

Chlorpyrifos is an organic phosphorous insecticide used to treat apples and pears. Consuming excessive amounts can cause convulsions or breathing difficulties.

The spinach was part of a total of 40 tons of frozen spinach imported by major trading firm Marubeni Corp. in February and April. It was used to make six different meals and sold at Lawson stores across the country.

Lawson, with more than 7,700 stores, disposed of all meals containing cooked spinach by May 27 and changed to domestic spinach May 31, company officials said.

In May, excessive quantities of pesticide residue were also found on frozen spinach from China used by restaurant chain Jonathan's Co.

Lawson, based in Tokyo, is listed on the Tokyo Stock Exchange's first section.