The US embassy on Wednesday ordered staff around the site of the February disaster in Zambia's northern copper belt to leave immediately, saying newly available information revealed the "extent of hazardous and carcinogenic substances".
The failure of the tailings dam released 50 million litres (13 million US gallons) of acidic waste from a Chinese-owned mine into streams and rivers near the town of Kitwe, about 285 kilometres (180 miles) north of the capital Lusaka.
After lime-dosing to neutralise the waste, pH levels in the water systems had returned to acceptable standards by early March and were now normal, government spokesman Cornelius Mweetwa told reporters.
Concentrations of heavy metals were also decreasing, he said.
"All serious implications on public health, water safety, agriculture, and the environment have been brought under control," he said.
"There is, therefore, absolutely no need to press the 'panic button' today to alarm the nation and the international community."
In a post on social media Wednesday, the US embassy said new information revealed the presence of hazardous substances including arsenic, cyanide, uranium and other heavy metals.
Ordering its US government personnel to leave the area, it said exposure to these toxins posed "immediate and long-term health threats".
The post did not say how many people were affected by the order or where the new information was from.
Without directly citing the US embassy, the Zambian government spokesman said anyone with new findings should bring them to the authorities.
No deaths or confirmed cases of acute heavy metal poisoning linked to the event had been recorded, Mweetwa said, and three people who had fallen ill had recovered.
The government was actively monitoring the presence of heavy metals in the water, soil and sediment, he said.
Of 200 soil and water samples being analysed by an independent laboratory, the preliminary results of 37 had been released and the remainder were undergoing testing, he said.
Media reports from the area soon after the disaster said the pollution had travelled more than 100 kilometres from the dam, killing fish and livestock.
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