Race against time to prevent second deluge of toxic sludge

• Workers in western Hungary have been labouring to build an emergency dam after fears another toxic sludge reservoir is about to burst. Pic: Getty

Over 184 million gallons of the waste material leaked out of the alumina plant reservoir into villages and waterways earlier this week, killing seven people, injuring 123 and fouling rivers, including a local branch of the Danube.

Kolontar was evacuated on Saturday after cracks appeared in the northern wall of the reservoir, threatening a second spill of the toxic red sludge, which swept through neighbouring areas last Monday, toppling cars and wreaking havoc in houses.

A by-product of alumina production, the thick, highly alkaline substance has a caustic effect on the skin. It contains heavy metals, such as lead, and is slightly radioactive. Inhaling its dust can cause lung cancer.

Treated sludge is often stored in ponds where the water eventually evaporates, leaving behind a largely safe red clay. Industry experts say the sludge in Hungary appears to have been insufficiently treated, if at all, meaning it remained highly caustic.

News agency MTI cited environment state secretary Zoltan Illes as saying a 25-metre-long crack in the weakened wall had widened slightly by yesterday morning and the wall of the damaged reservoir now looked beyond repair.

Mr Illes said the northern wall of the reservoir could collapse "within one day or a week" and crews at the scene were scrambling to complete a new dam to protect Kolontar and the nearby town of Devecser, home to 5,400 people.

Gyorgyi Tottos, a spokeswoman for disaster crews on the scene said authorities hoped to complete the 600-metre long and 5 to 7-metre tall dam within days to stop millions more gallons of sludge still in the reservoir from escaping.

"This wall will be able to stop the flow, experts hope to get it done within three days," Ms Tottos said.

"This is a race against time as good weather is forecast for the coming few days but then the rain will come.If we can have the dam finished by the time the rain comes, then it will be all right," she said.

Tottos added that the sludge still in the reservoir was thicker than the water-like substance which caused last Monday's disaster and authorities expected its spread to be slower and more contained, should a new spill occur.

Tibor Dobson, spokesman of disaster crews at the scene, said earlier that workers had laid the foundation of the new dam in Kolontar by yesterday morning.

Dobson said the number of people evacuated from Kolontar, which lies closest to the reservoir, had increased to about 1,000 overnight.

Prime Minister Viktor Orban has described the torrent of sludge as the worst ecological catastrophe Hungary has suffered.

The nearby town of Devecser remained on alert. The military has sent 319 soldiers and 127 transport vehicles into the town and five trains are ready in case it has to be evacuated.

Mr Dobson said around 400 to 500 people had decided to leave the town voluntarily and at this stage an evacuation was unlikely.

Mr Orban will inform parliament about the findings of an investigation today and promised "the toughest possible consequences" to ensure such a disaster does not recur.

The interior ministry said on its website that samples taken early yesterday showed that alkalinity levels in smaller rivers affected by Monday's spill, and in the Danube, had returned to normal.