The Zambian government sought to calm public concerns about pollution levels after a study found that the damage done by a disaster at a Chinese state-owned copper mine in February was much larger than officially reported.

“The water is fit for consumption,” Mike Mposha, Zambia’s minister of green economy and environment, told reporters in Lusaka, the capital, on Friday.

Laboratory tests received this week showed that Ph acidity readings were within safe levels in water tested in the region surrounding the mine, though there were elevated readings for manganese and zinc in four of the 23 places that were sampled, the minister said.

The partial collapse of a waste dam at the mine in Zambia’s northern Copperbelt Province may have released 30 times more toxic sludge into the environment than previously reported, Drizit Zambia Ltd. — appointed by Sino-Metals Leach to conduct an environmental audit of the accident — said in a June 3 letter.

It warned of persisting serious health risks from heavy metals contained in the spill, and described the incident as a “large-scale environmental catastrophe.”

Mposha declined to comment on Drizit’s assessment of the volume of the spill, saying it would be speculation as he has yet to officially received any such report.

Zambia is Africa’s second-biggest copper producer, and plans to more than triple output to 3 million tons by early next decade. The Zambian government last week played down the danger from the spill, saying there was no cause for alarm as the “immediate danger to human, animal and plant life has been averted.”

At least 50,000 tons of highly acidic mine waste escaped when the dam burst, according to official reports. Drizit estimated that more than 1.5 million tons were lost from the dam system in total — enough to fill more than 400 Olympic sized swimming pools.

Sino-Metals has apologized to the government, distributed initial compensation to farmers directly impacted, and paid a fine of 1.5 million kwacha (about $65,000). Another comprehensive impact assessment will take place after the company terminated its contract with Drizit to do the job, accusing it of contractual breaches. Drizit declined to comment.

Vulnerabilities around tailings storage have been in particular focus over the past decade after dam disasters at two Brazilian iron-ore mines owned by Vale SA, including a 2019 collapse that killed more than 272 people. Similar failures around the world over decades have resulted in deaths, destroyed property and caused massive environmental damage.