Effectiveness and ecotoxicity of zero-valent iron nanoparticles during rhizoremediation of soil contaminated with Zn, Cu, Cd and diesel

Effects of the application of an organic amendment and nanoscale zero-valent iron particles on soil Cr(VI) remediation

Chromium is considered an environmental pollutant of much concern whose toxicity depends, to a great extent, on its valence state, with Cr(VI) being more soluble, bioavailable, and toxic, compared to Cr(III). Nanoremediation is a promising strategy for the remediation of metal pollutants by changing their valence state. However, among other aspects, its effectiveness for soil remediation is seriously hampered by the interaction of nanoparticles with soil organic matter. In this study, soil was (i) amended with two doses of a municipal solid organic waste and (ii) artificially polluted with 300 mg Cr(VI) kg-1 DW soil. After a period of aging, a nanoremediation treatment with nanoscale zero-valent iron particles (1 g nZVI kg-1 DW soil) was applied. The efficiency of the remediation treatment was assessed in terms of Cr(VI) immobilization and recovery of soil health. The presence of the organic amendment caused (i) a decrease of redox potential, (ii) Cr(VI) immobilization via its reduction to Cr(III), (iii) a stimulation of soil microbial communities, and (iv) an improvement of soil health, compared to unamended soil. By contrast, nZVI did not have any impact on Cr(VI) immobilization nor on soil health. It was concluded that, unlike the presence of the organic amendment, nanoremediation with nZVI was not a valid option for soils polluted with Cr(VI) under our experimental conditions.

Gentle remediation options for soil with mixed chromium (VI) and lindane pollution: biostimulation, bioaugmentation, phytoremediation and vermiremediation

Gentle Remediation Options (GROs), such as biostimulation, bioaugmentation, phytoremediation and vermiremediation, are cost-effective and environmentally-friendly solutions for soils simultaneously polluted with organic and inorganic compounds. This study assessed the individual and combined effectiveness of GROs in recovering the health of a soil artificially polluted with hexavalent chromium [Cr(VI)] and lindane. A greenhouse experiment was performed using organically-amended vs. non-amended mixed polluted soils. All soils received the following treatments: (i) no treatment; (ii) bioaugmentation with an actinobacteria consortium; (iii) vermiremediation with Eisenia fetida; (iv) phytoremediation with Brassica napus; (v) bioaugmentation + vermiremediation; (vi) bioaugmentation + phytoremediation; and (vii) bioaugmentation + vermiremediation + phytoremediation. Soil health recovery was determined based on Cr(VI) and lindane concentrations, microbial properties and toxicity bioassays with plants and worms. Cr(VI) pollution caused high toxicity, but some GROs were able to partly recover soil health: (i) the organic amendment decreased Cr(VI) concentrations, alleviating toxicity; (ii) the actinobacteria consortium was effective at removing both Cr(VI) and lindane; (iii) B. napus and E. fetida had a positive effect on the removal of pollutants and improved microbial properties. The combination of the organic amendment, B. napus, E. fetida and the actinobacteria consortium was the most effective strategy.

Enhanced denitrification performance of Alcaligenes sp. TB by Pd stimulating to produce membrane adaptation mechanism coupled with nanoscale zero-valent iron

The microbial reduction of nitrate in the presence of nanoscale zero-valent iron (nZVI) was evaluated to assess the feasibility of employing nZVI for biological denitrification treatment. The effect of modified nZVI on the growth, metabolism, and denitrification performance of Alcaligenes sp. TB under aerobic conditions was studied. Results showed that Alcaligenes sp. TB with nZVI/Pd had 31.5% increase in nitrate removal and 18.1% decrease in nitrite accumulation within 28 h. nZVI/Pd exhibited less inhibition on the cell growth (OD₆₀₀ = 0.725), NADH/NAD⁺ ratio (86% of control), and electron transfer system activity (68.5% of control). In addition, nZVI/Pd decreased the membrane fluidity by increasing the trans/cis isomerization ratio (317.7% of control) to enhance the resistance of nZVI. This study underlines the effects of nZVI/Pd on membrane susceptibility via membrane fatty acid transformation during denitrification and suggests the influence of engineered nanomaterials on denitrification.

The nanotechnology among US: are metal and metal oxides nanoparticles a nano or mega risk for soil microbial communities?

Metal nanoparticles and metal oxides nanoparticles (MNPs/MONPs) have been widely included in a great diversity of products and industrial applications and they are already a part of our everyday life. According to estimation studies, their production is expected to increase exponentially in the next few years. Consequently, soil has been suggested as the main sink of MNPs/MONPs once they are deliberately or accidentally released into the environment. The potential negative perturbations that may result on soil microbial communities and ecological processes are resulting in concerns. Several nano-toxicological studies of MNPs/MONPs, reported so far, have focused on aquatic organisms, animals, and soil invertebrates. However, during recent years, the studies have been oriented to understand the effects of MNPs/MONPs on microbial communities and their interaction with soil components. The studies have suggested that MNPs/MONPs are one of the most toxic type to soil biota, amongst different types of nanomaterials. This may threaten soil health and fertility, since microbial communities are known to support important biological processes and ecosystem services such as the nutrient cycling, whereby their protection against the environmental pollution is imperative. Therefore, in this review we summarize the actual knowledge available from the last five years (2013-2018) and gaps about the potential negative, positive or neutral effects produced on soil by different classes of MNPs/MONPs. A particular emphasis has been placed on the associated soil microorganisms and biological processes. Finally, perspectives about future research are discussed.