Millions of litres of acidic waste were released into streams, rivers and fields near the town of Kitwe, about 285 kilometres (180 miles) north of the capital Lusaka after the tailings dam wall at the copper mine burst in February.

The Chinese firm and the Zambian government's responses to the incident have been under intense scrutiny after allegations from civil society and a pollution control firm that the spillage was far greater than claimed.

"The highly acidic and toxic substances caused severe environmental damage," said the complaint filed on September 12 on behalf of 176 residents of the area against Sino-Metals Leach, the owner of the tailings dam, and NFC Africa Mining, which owns the surface area on which it was situated.

The applicants said the spill had killed aquatic life, flooded fields and homes, scorched crops and pastures, led to the death of livestock and "induced abject poverty".

- $80 billion -

Exposure to the pollution has caused "a range of immediate health issues" from abdominal pains to skin irritations, respiratory issues, vomiting and blood in urine, they said.

They are demanding $80 billion be deposited into an escrow account as a "security for environmental reparation, remediation, and restoration and full compensation" and for 8,000 Zambian kwacha ($344) per month to temporarily relocate outside of the polluted area.

Sino-Metals Leach announced about 50 million litres of waste had been spilled, but a pollution control company said the amount was about 20 times greater.

The company, Drizit, had been hired through a government tender to assess the damage and clean up the environment, but its contract was drawn up with Sino-Metals Leach.

Drizit said its studies found the waste contained "dangerous levels of cyanide, arsenic, copper, zinc, lead, chromium, cadmium", which present severe health risks including cancer and birth defects, according to the World Health Organization.

But "Sino Metals terminated the contract one day before the final report was due", Drizit said.

- Toxic current -

According to environmental groups, the waste contaminated a branch of one of Zambia's longest rivers, the Kafue.

In the court documents, farmers said they "were shocked to witness a sudden increase of floodwater that... necessitated abandoning some homes, fields and gardens out of fear of drowning and being swept by the strong current".

"We had never witnessed such in our lifetime," they said, adding that they walked through the water barefoot as "they had no information that the water was highly toxic".

Human Rights Watch last week urged the Zambian government to investigate the health fallout of the spill.

Sino-Metals Leach produced 5,754 tonnes of copper cathodes in 2024 from its operations in Chambishi, the site of the incident, according to the latest annual report from its holding company, China Nonferrous Mining (CNMC).

CNMC did not immediately respond to AFP's request for comment.