Three companies each purchased more monazite, which contains radioactive substances, than the mattress maker for Daijin Bed, a lawmaker said on Wednesday amid rising public anger over mattresses emitting dangerous levels of radioactive material.

The Nuclear Safety and Security Commission announced last week that some of Daijin Bed’s mattresses emitted radon at levels of up to 9.3 times the national safety standard.

Long-time exposure to radon -- a colorless, odorless, radioactive gas -- can lead to lung cancer.

The inner covers of the mattresses were coated with negative ion powder, which the commission identified as monazite, a reddish-brown mineral that contains radioactive substances.

According to data released by Rep. Kwon Chil-seung of the ruling Democratic Party, the manufacturer of mattresses for Daijin bought 2,960 kilograms of monazite between 2013 and 2016 from the only company in Korea that imports the mineral.

The importer sold a total of 40,657.5 kilograms of monazite to 66 firms from January 2013 to April 2018.

A company that sells bracelets and laundry balls bought some 12,000 kg of monazite between 2014 and 2018.

Two more firms purchased more monazite than Daijin’s mattress maker.

Eighteen other companies bought hundreds of kilograms of the mineral.

“It is possible that more firms could have used monazite as the authorities have not kept track of its supply and demand until now,” Kwon said.

“The Nuclear Safety and Security Commission should conduct a complete survey and disclose its findings to prevent additional damage.”

By Kim So-hyun (sophie@heraldcorp.com)