Soot spewed out by the blaze over some agricultural areas was “liable to present a public health risk that requires us to take immediate measures on a precautionary basis”, the regional administration said.
It added in decrees published on Sunday that in the absence of food safety guarantees from producers, anything likely to have been exposed to contamination would have to be destroyed.
Around 100 districts in the area surrounding Rouen are expected to have been affected.
On Friday, France’s health minister Agnes Buzyn said she could not guarantee there was no risk to the public from the pollution caused by the fire. Schools and creches, which shut following the fire due to safety concerns, open Monday.
The huge blaze erupted on Thursday in a storage facility owned by Lubrizol, a manufacturer of industrial lubricants and fuel additives owned by the billionaire American investor Warren Buffett.
Firefighters took hours to put out the fire, which erupted at around 2:30am (0030 GMT) Thursday at the storage facility.
The Lubrizol plant sits just a few kilometres from the centre of Rouen, a city of some 100,000 people. The smoke spread 22 kilometres (14 miles).
Lubrizol said the fire damaged a storage facility, a drumming warehouse and an administrative building.
Prosecutors launch inquiry
French Interior Minister Christophe Castaner, visiting the site Thursday, said firefighters had managed to remove “the most dangerous products” that could have provoked other explosions at other nearby industrial sites.
The smoke contained “a certain number of compounds which can be a health hazard”, Castaner said, though there was no “particular danger” according to initial analyses.
Prosecutors have launched an inquiry into the cause of the explosion and fire, which woke up residents with a booming explosion.
Pierre-Andre Durand, the top regional official, said that there was a risk that fuel or waste water from the site could overflow retainment ponds and reach the Seine, and that floating anti-pollution booms had been placed on the river.
“There is no pollution downstream,” he said, and while some could escape as the tide came in, “it will be easy to recover because it’s on the surface.”
The Seine, one of France’s biggest rivers, flows through Paris to the south and empties into the English Channel further north in Le Havre, which is home to a major fishing fleet.
In January 2013, the Lubrizol factory was responsible for a giant leak of the gas mercaptan, which smells like cabbage or rotten eggs and is often added to natural gas to alert people in case of leaks.
A cloud of the gas blew all the way to Paris and across the Channel into southern England, where residents complained about the odour.
And in 2015, 2,000 litres of mineral oil, which is used in lubricants, leaked from the Lubrizol site into the local sewer system in Rouen, which is famed for its cathedral.