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Nanoremediation and long-term monitoring of brownfield soil highly polluted with As and Hg

Gil-Díaz, M., Rodríguez-Valdés, E., Alonso, J., Baragaño, D., Gallego, J.R., Lobo, M.C.
The Science of the total environment 2019 v.675 pp. 165-175
arsenic, iron, laboratory experimentation, leaching, mercury, monitoring, polluted soils, pollution load, remediation, toxicity
In the last decade, several laboratory-scale experiments have shown the use of nanoscale zero-valent iron (nZVI) to be effective in reducing metal(loid) availability in polluted soils. The present study evaluates the capacity of nZVI for reducing the availability of As and Hg in brownfield soils at a pilot scale, and monitors the stability of the immobilization of these contaminants over a 32 month period. To the best of our knowledge, this is the first study to apply nZVI to metal(loid)-polluted soils under field conditions. Two sub-areas (A and B) that differed in pollution load were selected, and a 5 m2 plot was treated with 2.5% nZVI (by weight) in each case (Nanofer 25S, NanoIron). In sub-area A, which had a greater degree of pollution, a second application was performed eight months after the first application. Overall, the treatment significantly reduced the availability of both As and Hg, after only 72 h, although the effectiveness of the treatment was highly dependent on the degree of initial contamination. Sub-area B (with a lower level of pollution) showed the best and most stable immobilization results, with As and Hg in toxicity characteristics leaching procedure (TCLP) extracts decreasing by 70% and 80%, respectively. In comparison, the concentrations of As and Hg in sub-area A decreased by 65% and 50%, respectively. Based on our findings, the use of nZVI at a dose of 2.5% appears to be an effective approach for the remediation of soils at this brownfield site, especially in sub-area B. For sub-area A, a higher dose of nZVI—or its use in combination with other remediation strategies—should be tested.