It became an offence earlier this month for seafood to be collected at Dalgety Bay in Fife after emergency measures were imposed.
The extension of the order, which originally lasted for 28 days, has been agreed by MSPs at Holyrood’s Health Committee.
The move was a “precautionary measure” because of radioactive items on the beach, the Food Standards Agency (FSA) in Scotland explained at the time.
Beachcombers are known to collect shellfish, although there is no commercial fishing or shellfish industry in operation in the area.
Warning signs had been in place at the beach for some time but new evidence indicated that radioactive particles could be ingested by fish, including shellfish, the FSA said.
Last month an investigation plan to establish how to clean up the beach was agreed by the Ministry of Defence and the Scottish Environment Protection Agency (Sepa).
The environmental body said then that it expects “remediation action to follow urgently” at the conclusion of the investigation.
Health Minister Mr Matheson said: “The Food Standards Agency will review this order in light of new data from this work as well as data from seafood sampling being undertaken jointly by the Food Standards Agency and Sepa.
“The order will also be reviewed if remedial works are subsequently undertaken, which successfully remove the pathway by which particles could enter the food chain.”