Greenpeace has warned of "surprisingly high" levels of arsenic and mercury in the red sludge that burst out of a metals plant reservoir in Hungary, killing six people and devastating the surrounding area.
Environmental activists said samples taken on Tuesday in Kolontar, the worst-hit village in western Hungary, showed 110mg of arsenic, 1.3mg of mercury per kg of dry matter and 660mg of chrome per kg.
The figures could roughly be translated as 50 tonnes of arsenic, 300 tonnes of chrome and 500kg of mercury set free by the spill, Greenpeace officials said.
"This contamination poses a long term risk to both the water base and the [surrounding] ecosystem," the group said in a statement on Friday.
"As long as the environment is alkaline, these materials are bound in the mud. As soon as the alkalinity is reduced ... these heavy metals are gradually released to the environment."
The information contrasts with that given earlier in the week by Hungary's National Academy of Sciences, which said there were no heavy metals or mercury in the sludge that exceeded the normal environmental limit.
Hungary's interior minister said there was a limited risk of biological or environmental catastrophe in the Danube river, which was hit by the sludge on Thursday.
Sandor Pinter said alkalinity levels from the alumina plant spill had decreased since Monday to a pH of around nine, well below the 13.5 measured in local waterways first hit by the torrent.
"Let's not even consider the pollution that got into the Danube as real pollution now, as the material that got into the river has pH levels of below nine, which, considering the [large volume of] water, will dilute in a few kilometres," he told a news conference.
"It will not be of an extent which would cause biological or environmental damage," Pinter said.
Monitors in Hungary and in countries downstream on the Danube, including Croatia, Serbia and Romania, are checking the quality of the river every few hours.
Sporadic losses of fish have been recorded in the main branch of the Danube, Hungary's disaster relief services said, but added that it had not seen the same level of devastation that hit local waterways.
Officials said on Thursday that life had been extinguished from the Marcal river, which was struck by the spill first.
There are also fears that a change in the weather could pose greater health problems to local residents.
Zoltan Illes, the environment minister, said as rain gave way to dry, warmer weather over the past two days, the caustic mud is increasingly turning to airborne dust, which can cause respiratory problems and potentially lung cancer.
"If that would dry out then ... wind can blow ... that heavy metal contamination through the respiratory system," he said.
Illes said the long-term effects on the agricultural region were devastating, saying around 809 hectares of topsoil would have to be dug up and replaced because the highly alkaline sludge had killed off all the nutrients and organisms needed to keep the soil healthy.
The company at the centre of of the leak said released $150,000 to local authorities to help deal with the disaster, and offered its condolences to the relatives of those who had lost their lives.
MAL, the Hungarian Aluminium Production and Trade Company, has come under fierce criticism, with officials suggesting too much of the caustic red sludge was being held in the reservoir.
Authorities have ordered a criminal inquiry into the accident.
MAL insists it has done nothing wrong and that the sludge is not considered hazardous under EU standards.
Tania Page, Al Jazeera's reporter in Kolontar, said 34 homes in the village have been made completely uninhabitable and that authorities said it may take up to a year to get the affected area back to normal.
"The locals have hired themselves a top lawyer. They're all pointing their fingers at the company [MAL]. The government also wants answers."
A man injured in the toxic spill died in hospital early on Friday, while another body was recovered from a sludge-covered area in the village of Devecser later in the day, bringing the death toll to six.
Authorities said the volume of the spill was 700 cubic metres, equal to the Gulf of Mexico oil spill.
Viktor Orban, Hungary's prime minister, has described the spill as a natural disaster unprecedented in Hungary.
"If this had happened at night then everyone here would have died," he said as he visited on of worst affected villages. "This is so irresponsible that it is impossible to find words!"
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