The potential to produce safe textiles in a phytoattenuation strategy: The fate of Cd and Pb during industrial treatments on contaminated hemp fibers

Abstract

Industrial hemp (Cannabis sativa L.) is getting increased attention as a sustainable alternative to synthetic fibers and cotton in the textile industry, as well as a candidate for phytoremediation, as it has been shown to tolerate stress from heavy metal-contaminated soil and experiences no or only little decrease in yields. With the EU Soil Strategy of 2030 promoting land reuse, hemp could be a perfect candidate for fiber production for textiles while growing on heavy metal contaminated land and restoring the soil. This strategy, combining safe biomass production and land valorization, is called phytoattenuation. In this study, Cd and Pb-contaminated hemp fibers underwent demineralization and bleaching treatments, commonly used in the textile industry. Total and extractable Cd and Pb concentrations were analyzed and assessed against legal safety thresholds and toxicity thresholds used in the textile industry to evaluate the safety of these fibers for textile production. Total and extractable Cd and Pb concentrations were below the total (40 mg/kg Cd and 90 mg/kg Pb) and extractable (0.1 mg/kg Cd and 1.0 mg/kg Pb) safety limits in the treated fibers after the combined demineralization and bleaching treatments. To understand in which parts of the fiber Cd and Pb are concentrated, fibers were analyzed for their cellulose, hemicellulose, and lignin content after each treatment. Extractives such as pectin were removed during demineralization and bleaching removed part of the lignin and hemicellulose. This corresponded respectively to a decrease in Cd and Pb, suggesting that Cd is rather bound to pectin in the primary wall, while Pb could be bounded to lignin and hemicellulose in the secondary wall of the fiber. However, the fate of the elements in the fiber remains complex. Overall, the results are promising for safe textile production from hemp fibers grown on Cd and Pb-contaminated soil.