Toxic red sludge from a Hungarian aluminium oxide plant reached the Danube on Thursday and crews struggled to dilute it to protect the river from what the prime minister called an “unprecedented ecological catastrophe.”
Experts said damage beyond the borders of Hungary was unlikely to be great, but the threat had to be monitored closely.
Tibor Dobson, a spokesman for Hungarian disaster crews, told Reuters there were sporadic fish deaths in the Raba and the Mosoni-Danube rivers. He said all fish had died in the smaller Marcal River, which was hit by the spill first.
Crews were working to reduce the alkalinity of the spill, which poured out of the burst containment reservoir of an alumina plant on Monday and tore through local villages, killing four people and injuring over 150. Three are still missing.
The spill’s alkaline content when it reached the Raba, the Mosoni-Danube and the Danube itself, was still around pH 9 — above the normal, harmless level of between 6 and 8.
Crews were pouring hundreds of tons of plaster and acetic acid into the rivers to neutralize the alkalinity.