A Catalyst for Disaster
From 1950 to 1997, a factory near the industrial city of Temirtau produced acetaldehyde, a precursor for synthetic rubber. The chemical process used mercury salts as a catalyst. Due to inefficient Soviet-era technology and a wastewater treatment plant not designed to handle heavy metals, enormous quantities of mercury were discharged directly into the Nura River. Estimates of the total amount released over 47 years vary, with the World Bank reporting a figure of more than 1,500 tons.
The mercury did not wash away. It settled into the riverbed, binding with fly ash from nearby power stations to create a unique and dangerous type of sediment sometimes called "technogenic silt". This toxic sludge accumulated over decades, creating a massive reservoir of contamination. The highest concentrations of mercury were found in the first 15 kilometers downstream from the factory, with average concentrations in the riverbed measuring between 150 and 240 mg/kg. In some hotspots at the industrial site itself, contamination levels were 150 times higher than international standards.
The Long Tail of Contamination
The closure of the acetaldehyde plant in 1997 stopped the primary source of pollution, but the mercury already in the ecosystem was a persistent threat. Elemental mercury can be transformed by microorganisms in river sediments into methylmercury, a potent neurotoxin. This organic form of mercury bioaccumulates, moving up the food chain from small aquatic organisms to fish, and ultimately to humans who consume the fish. Studies of the local population revealed that nearly 17% of people tested had mercury levels in their hair that exceeded the reference dose set by the U.S. Environmental Protection Agency.
In 2003, the Government of Kazakhstan and the World Bank launched the Nura River Cleanup Project, a massive remediation effort. The project involved excavating highly contaminated soil and sediment from the 60-hectare factory site and an 18-kilometer stretch of the river's banks and floodplains. This toxic material, totaling over two million tonnes, was transported to a specially constructed hazardous waste landfill. The factory itself was demolished between 2008 and 2009. The project also included reinforcing the Intumak Reservoir dam to control water flow and prevent contaminated floodwaters from spreading further downstream.