No metallic or organic contaminants have entered the Danube from the red sludge spill in western Hungary due to decontamination efforts made along the Marcal, its tributary, the National Disaster Management said Sunday.

In Gonyu, the village where the sludge spill entered the Danube, the PH level of the Danube was down to 7.54, almost neutral, in Sunday's measurements.

However, disaster management is on alert to prevent another wave of contaminants from breaking free of the damaged reservoir containment wall, where one million cubic meters of the highly caustic (PH 13) sludge broke out, leaving three villages inundated, seven dead and 150 hospitalized with alkali burns.

Decontamination efforts involved pouring tons of plaster into the waterways to bind the polluted water and doses of acetic acid to neutralize the alkaline sludge. Other measures forced the contaminants to settle on the creek and river beds.

Meanwhile, Environment Minister Zoltan Illes said the damaged containment wall was unsalvageable. The northern wall of the sludge reservoir will definitely give way, he said on Sunday.

"We don't know whether it will last another day or another week, but tragedy can strike at any moment," he said, adding that current efforts were to protect the homes still left in the villages of Kolontar and Devecser with a barrier currently under construction.

Experts agreed that the reservoir wall will collapse, but it may be possible to keep the red mud from spilling out, and to eventually transfer it to another reservoir, Illes said.

It is estimated that the reservoirs contain another two and a half million cubic meters of red mud that should not spread out more than one to one and half kilometers if the wall gives way, he added.

The minister said the reservoir will be safe only when it is completely closed down and its contents are transferred to another reservoir to be built.