|There are fears that when the red sludge dries out it will pose an even greater health hazard [Reuters]
Red sludge from an aluminium plant has devastated several towns in western Hungary, killing four people and leaving at least one hundred others with chemical burns and irritations.
Al Jazeera takes a look at what dangers the toxic mud is posing to the area and its potential long-term impact.
What is red sludge?
Taking its name from its deep red colour, the material is a by-product of aluminium production, in which bauxite is refined into the metal.
As a result it can contain heavy metals such as lead, cadmium, arsenic and chromium, and also slightly radioactive material - although it is not yet clear precisely what elements are present in Hungary's mud spill.
The most concerning aspect of the sludge currently appears to be the high levels of alkaline in the liquid.
Simon Gergely, a member of the Clean Air Action group, an environmental NGO in Hungary, told Al Jazeera that the Ph, or alkaline levels, of the mud is at around 13, meaning it is highly corrosive and acts as an irritant.
"The alkaline can be absorbed through the skin. The main compounds are iron oxide and aluminium oxide, and so most parts of it are not toxic, but as it contains alkaline it is very caustic," he said.
There have been conflicting reports about whether the sludge contains radioactive material, but according to workers on the ground, early tests have not found evidence of radiation.
According to MAL, the Hungarian Aluminum Production and Trade Company that owns the Ajka plant, red sludge is not considered hazardous waste under European Union standards.
What risks does it pose to those who come in contact with it?
Already hundreds of people have been treated for chemical burns after coming into contact with the sludge. It is not clear yet whether the four killed suffered burns or drowned in the flood after the reservoir burst its banks.
But according to Benedek Javor, chair of Hungary's National Sustainable Development Committee, the sludge could pose bigger health problems once it dries out.
"While it's still wet on the ground it cannot reach the respiratory system," he told Al Jazeera.
"As it contains heavy metals and other elements it could be really dangerous, [causing] lung cancer and respiratory problems. In the body it can also get into the blood system through the lungs."
Gergely added that the dried sludge would be "totally poisonous" to people who breathe it in.
What has been the environmental impact so far?
The torrent of sludge has poured into fields and nearby streams, killing animals and fish in the region.
It also poses a threat to the local farming industry, Gabor Figeczky, the acting director of the World Wildlife Fund in Hungary, told Al Jazeera.
"It's an agricultural area so I would say there can be no crops produced for human consumption for quite some time. And we still don't have the data ... so the consequences could even be longer," he said.
Javor said studies will have to be done to find out what metals are appearing in the soil and in the waterbase in the region.
Is the water supply affected?
According to Figeczky, the toxic waste has not contaminated the water supply.
"If the water had gone into the other direction where there's a drinking water supply then it would have been a much bigger disaster," he said.
But there are serious fears that the sludge could pollute the Danube River, one of Europe's major waterways.
Emergency workers have already poured tonnes of plaster into the Marcal River, a tributary to the Danube, in an attempt to bind it and stop it spreading.
The Danube is Europe's second largest river and flows through Croatia, Serbia, Romania, Bulgaria, Ukraine and Moldova before emptying into the Black Sea.
Figeczky said it was not easy to assess at this stage what the damage would be if it did enter the waterway.
"No one knows how concentrated the liquid will be if it gets to the Danube," he said.