Abstract
Little attention has been given to the development of remediation strategies for soils polluted with mixture of pollution (metal(loid)s and organic compounds). The present study evaluates the effectiveness of different types of commercial iron nanoparticles (nanoscale zero valent iron (nZVI), bimetallic nZVI-Pd, and nano-magnetite (nFe3O4)), for the remediation of an industrial soil co-contaminated with Cr and PCBs. Soil samples were mixed with nZVI, nZVI-Pd, or nFe3O4 at doses selected according to their reactivity with PCBs, homogenized, saturated with water and incubated at controlled conditions for 15, 45 and 70 days. For each sampling time, PCBs and chromium were analyzed in aqueous and soil fractions. Cr(VI) and Cr leachability (TCLP test) were determined in the soil samples. The treatment with the three types of iron nanoparticles showed significant reduction in Cr concentration in aqueous extracts at the three sampling times (> 98%), compared to the control samples. The leachability of Cr in treated soil samples also decreased and was stable throughout the experiment. Results suggested that nZVI and nZVI-Pd immobilized Cr through adsorption of Cr(VI) on the shell and reduction to Cr(III). The mechanism of interaction of nFe3O4 and Cr(VI) included adsorption and reduction although its reducing character was lower than those of ZVI nanoparticles. PCBs significantly decreased in soil samples (up to 68%), after 15 days of treatment with the three types of nanoparticles. However, nFe3O4 evidenced reversible adsorption of PCBs after 45 days. In general, nZVI-Pd reduced PCB concentration in soil faster than nZVI. Control soils showed a similar reduction in PCBs concentration as those obtained with nZVI and nZVI-Pd after a longer time (45 days). This is likely due to natural bioremediation, although it was not effective for Cr remediation. Results suggest that the addition of nZVI or nZVI-Pd and pseudo-anaerobic conditions could be used for the recovery of soil co-contaminated with Cr and PCBs.
Highlights
Little attention has been given to the development of remediation strategies for soils polluted with mixture of pollution (metal(loid)s and organic compounds)
The addition of nanoscale zero valent iron (nZVI), nZVI-Pd or n Fe3O4 to a soil co-contaminated with Cr and PCBs significantly reduced the leachability of Cr in soil and the immobilization was stable for at least 70 days under the experimental conditions
After 15 days of interaction between soil-nanoparticles, the PCBs concentration significantly decreased in soils treated for the three types of iron nanoparticle
Summary
Little attention has been given to the development of remediation strategies for soils polluted with mixture of pollution (metal(loid)s and organic compounds). Control soils showed a similar reduction in PCBs concentration as those obtained with nZVI and nZVI-Pd after a longer time (45 days) This is likely due to natural bioremediation, it was not effective for Cr remediation. The remediation of co-contaminated soils is often more complicated due to the interactions among pollutants including changes of solubility, speciation and bioavailability, competition for the binding sites of adsorbents and inhibition of microbial metabolism which can conduct to synergistic and antagonistic effects on the remediation results[22] In this regard, some researches have been focused on the remediation of co-contaminated soils with organic compounds and metal(loid)s including bioremediation, phytoremediation, treatment with agents and combined techniques such as electrokinetic-bioremediation[22–25]. The exposure to PCBs, metals and metalloids poses a serious risk for both human health and the environment, the development of effective remediation techniques is very important and should be prioritized[26]
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