Enhancing arsenic phytoremediation through graphene oxide–induced mobilization in polluted mining soils

Soil contamination derived from abandoned mining sites represents one of the most persistent environmental threats in Europe and worldwide. In regions such as the Principality of Asturias (NW Spain), historical mercury mining has generated large areas of affected sites, where soils exhibit high concentrations of arsenic (As) and mercury (Hg). In recent years, the use of engineered nanomaterials has emerged as a promising approach to modify contaminant mobility in soils, either by enhancing immobilization or by improving extractability. However, significant uncertainties remain regarding the behavior of metalloids such as arsenic (As), whose interactions with soil minerals may differ substantially when nanomaterials are introduced. This study evaluates whether graphene oxide (GOx) can enhance As phytoremediation, focusing on plant uptake and accumulation in a mining polluted soil. A pot experiment was conducted using soil (S) from El Terronal, an abandoned mining site, and soil amended with 1% GOx nanoflakes (SGO). Eupatorium cannabinum plants were transferred to the pots (n = 10 per treatment) and grown for 7 and 30 days. Plant performance (biomass, shoot/root length) and As concentration and speciation in tissues were determined. Soil physicochemical properties, total concentration, As availability (TCLP), and As fractionation (Wenzel method) were analysed.

GOx significantly modified As dynamics in the soil-plant system. Leaching tests revealed higher As release in GOx-amended soils, likely due to FeOOH dissolution and reduction, as well as protonation of GOx under acidic leaching conditions (soil pH decrease after GOx application). Plant uptake showed that GOx enhanced As retention in roots, promoting phytostabilization rather than phytoextraction. After 30 days, As concentration in roots increased markedly in SGO (442 mg kg⁻¹; As(III): 11.1%) compared to S (38.5 mg kg⁻¹; As(III): 5.4%). Shoots also showed higher As content in plants growing in the SGO treatment (73.0 mg kg⁻¹; As(III): 15.8%) than in S (21.3 mg kg⁻¹; As(III): 11.6%). However, translocation factors (TF) remained <1 in all cases (S: 0.76; SGO: 0.17), indicating restricted movement of As to aerial tissues. Bioaccumulation factors (BAF) exceeded 1 in both soils and increased under GOx (S: 1.96; SGO: 3.94), reflecting enhanced As accumulation rather than translocation.

Overall, GOx enhanced arsenic accumulation in roots, highlighting its potential for phytostabilization-based remediation strategies. These results provide important insights into the behavior of GOx in real contaminated soils and emphasize the evaluation of nanoremediation technique as post-mining soil restoration solution.

References:

[1] Baragaño, D., Forján, R., Welte, L., & Gallego, J.R. (2020). Nanoremediation of As and metals polluted soils by means of graphene oxide nanoparticles. Scientific Reports 10(1), 1896

[2] Peña-Álvarez, V., Baragaño, D., Prosenkov, A., Gallego, J.R., Peláez, A.I. (2024). Assessment of co-contaminated soil amended by graphene oxide : effects on pollutants, microbial communities and soil health. Ecotoxicology and Environmental Safety 272, 116015.

Acknowledgements:

This work was funded by the research project RESIST, PID2024-160647OB-I00 (MICIU/AEI/10.13039/501100011033/FEDER, EU). Bryan Salgado-Almeida acknowledges the Spanish National Research Council for the "JAE Intro ICU 2025" fellowship (Ref. CN-IGME-03).