Chromated copper arsenate (CCA) is widely used globally as a waterborne inorganic wood preservative, acting as a fungicide and insecticide to prevent timber damage. Toxic metals (Cr, As, and Cu) can leach into the environment, posing risks, and a thorough understanding of the immobilisation agents used to prevent leaching is lacking. This study systematically investigated the leaching behaviour of As, Cr, and Cu from fresh and weathered CCA-treated timber in block and mulch forms under simulated rainfall conditions. The effectiveness of selected immobilisation agents (iron sulfate, bentonite, iron powder, and steel wool) was evaluated for their ability to lock up and immobilise toxic metal(loid)s from leaching out via a column study. Column experiments were conducted over 15 weeks to quantify metal(loid)s release and treatment performance. Compared with fresh timber, weathered timber exhibited sustained and greater metal(loid)s leaching, with arsenic showing the most significant mobility. Among the immobilisation agents tested, iron powder and steel wool markedly reduced metal(loid)s leaching, resulting in a >99% reduction in As and substantial reductions in Cr and Cu. Speciation, SEM–EDS, and XRD analyses revealed that zero-valent iron promoted the reduction of Cr(VI) to Cr(III) and facilitated adsorption, co-precipitation, and the incorporation of As and Cr into newly formed iron (oxyhydr)oxide and mixed Fe–As–Cr mineral phases, thereby decreasing metal mobility. Notably, steel wool treatment increased both bacterial and fungal diversity in the timber mulch, indicating reduced toxicity following immobilisation. Overall, this study demonstrates that iron-based amendments, particularly steel wool, provide a practical, mechanistically robust approach for immobilising toxic metals in CCA-treated timber, supporting safer, risk-based management and reuse strategies.
- Open Access
- Article
Influence of Immobilisation Agents on the Leaching Behaviour of Copper, Arsenic, and Chromium from Chromated Copper Arsenate-Treated Timber
Author Information
Received: 17 Oct 2025 | Revised: 22 Dec 2025 | Accepted: 12 Jan 2026 | Published: 20 Jan 2026
Abstract
Keywords
CCA-treated timber | leaching of trace elements | immobilisation agent | iron | arsenic | chromium
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