The spill last October of around one million cubic metres of highly alkaline red sludge from a reservoir at a Hungarian aluminia plant near Ajka raised serious health concerns. But dust from the 3 to 30 centimetre-thick layer of mud is fortunately not quite as harmful as first feared, Hungarian scientists report in the journal Environmental Science & Technology.

The group analysed the particle size distribution and mineralogical properties of dust from red mud sediment that has gathered in the 700 hectares disaster region some 100 kilometres southwest of Budapest.

The sediment and its dust are similar in their chemical composition, both containing the minerals hematite, cancrinite, calcite, and hydrogarnet, the scientists report. The volatility and alkalinity of the dust could pose minor respiratory and eye problems to humans. But the particles, if inhaled, are too large to affect the deep regions of the lungs, they say.

“Based on its size distribution and composition red mud dust appears to be less hazardous to human health than urban particulate matter,” they conclude.

Hungarian scientists have previously reported relatively low levels of toxic heavy metals in drinking water from the contaminated area. However, soil samples taken shortly after the spill by Greenpeace contained high concentrations of Arsenic.

UPDATE 9 February: The latest samples taken by Greenpeace, on 26 January, still show contamination, the BBC is reporting. And they are threatening a local river that is part of the Danube river system.

Image: ES&T