The Valais Department of Mobility, Spatial Planning and Environment confirmed on Tuesday that Lonza has completed the main phase of mercury remediation in Upper Valais, concluding a decade-long effort to remove contamination linked to the pharmaceutical supplier’s historical wastewater discharges.
A total of 3.5 tonnes of mercury were extracted from approximately 170,000 square metres of soil across Raron, Niedergesteln and Visp. The contamination originated from decades of mercury-laden wastewater released into the Rhône via the Grossgrundkanal, with polluted sediments later spreading to gardens and agricultural land.
Remediation efforts spanned two distinct phases. Residential areas, covering over 100,000 square metres and 174 parcels, were addressed first starting with pilot tests in 2016 and systematic cleanup in 2017. Soils exceeding 2 milligrams of mercury per kilogram were excavated and replaced with clean material.
Agricultural land, covering about 60,000 square metres with mercury concentrations above 7 milligrams per kilogram, underwent large-scale remediation beginning in 2023. The process included two years of specialized soil management to preserve fertility and structural integrity.
The total cost of the project reached 51 million Swiss francs, with Lonza covering 93.5% of the expense at approximately 47.5 million francs. The canton of Valais contributed 2 million francs, while municipalities accounted for the remaining 1.5 million francs.
Environmental groups Ärzte für Umweltschutz and WWF hailed the completion as a significant success for public health and ecosystems, noting in a joint statement that the mercury pollution posed ongoing risks to humans and wildlife. Further investigations into the Grossgrundkanal’s contamination status remain underway.
A separate remediation project at the former Lonza landfill in Gamsenried is scheduled to commence by the end of 2026 or early 2027.
