Long-term efficiency of metal immobilization by soil amendments in a metal contaminated area in Austria

The presence of non-essential metals threatens agricultural productivity and food safety in many regions of Europe, particularly where historical contamination coexists with ongoing land use. Gentle remediation options, such as soil amendments coupled with appropriate vegetation, offer cost-effective and environmentally compatible means to reduce metal mobility and exposure risk, while restoring safe, productive use on contaminated land. Within this context, this study investigated a historically metal-impacted field in Arnoldstein (Carinthia, Austria) to assess amendment-driven immobilization and its persistence over time.

Arnoldstein has a long history of Pb-Zn mining and smelting dating back to the 15^th century. Despite the smelter’s closure in 1992, elevated Cd, Pb and Zn concentrations remain in the topsoil in the surrounding area, exceeding national assessment values for agricultural and horticultural use and constraining safe biomass production.

Building on prior studies that tested various amendments, a field experiment was established in Arnoldstein in 2013-2014 to compare an organic (poplar N-enriched biochar, P-BC), a mineral amendment (gravel sludge plus iron oxide, GSFe), and their combination (P-BC + GSFe) for aided phytostabilisation using Miscanthus x giganteus. Amendments were applied at a rate of 1% (w/w) to a depth of 10 cm. Across treatments, NH₄NO₃-extractable Cd, Zn and Pb in the amended topsoil were significantly reduced relative to control. Metal concentrations in miscanthus shoots remained low and were largely unaffected by treatment, indicating limited translocation despite improved immobilization in soil.

Within the Interreg project “PoLaRecCE”, the site was revisited in autumn 2024, after a decade without active management, to evaluate the long-term performance of the soil amendments. Resampling showed that reduced bioavailability of Cd, Zn and Pb persisted, demonstrating durable field-scale immobilization beyond short-term effects under real field conditions without intensive management. The current phase extends the assessment to soil health indicators to evaluate broader functional recovery.