Enhanced phytoremediation of Metal(loid)s via spiked ZVI nanoparticles: An urban clean-up strategy with ornamental plants.

The increasing industrialization and urbanization are also triggering environmental pollution, mostly unnoticed, in the case of soil pollution due to uncontrolled contamination by toxic elemental dispersion. The present study focused on this aspect and studied the clean-up of urban soil in a low-cost and eco-friendly way to restrict arsenic (As), lead (Pb) and mercury (Hg) contamination. Four potential ornamental plants, Catharanthus roseus (vinca), Cosmos bipinnatus (cosmos), Gomphrena globose (globosa) and Impatiens balsamina (balsamina) were used along with zero valent iron (ZVI) nanoparticles (Fe NPs) for remediation of the soil spiked with As (70 mg kg-1), Pb (600 mg kg-1) and Hg (15 mg kg-1) in a 60 d pot experiment. All plants were divided into four groups viz. control, spiked, spiked+20 mg kg-1 ZVI NP and spiked+50 mg kg-1 ZVI NP. FTIR and SEM were used for ZVI NP characterization. Soil and plant analyses and elemental assessments were done using ICP-MS, XRF and SEM. Among the four plants, cosmos showed the maximum accumulation of toxic elements (41.24 ± 0.022 mg kg-1 As, 139.15 ± 11.2 mg kg-1 Pb and 15.57 ± 0.27 mg kg-1 Hg) at 60 d. The application of ZVI NP at 20 mg kg-1 dosage was found to further augment plants' potential for metal(loid)s accumulation without negatively hampering their growth. Cosmos were observed to reduce soil As from 81.35 ± 1.34 mg kg-1 to 28.16 ± 1.38 mg kg-1 (65.38%), Pb from 1132.47 ± 4.66 to 516.09 ± 3.15 mg kg-1 (54.42%) and Hg from 17.35 ± 0.88 to 6.65 ± 0.4 mg kg-1 (61.67%) at 60 d in spiked + 20 mg kg-1 ZVI NP treatment. Balsamina was the most sensitive plant and showed the least metal(loid)s accumulation. In conclusion, three of these plants are potent enough to use together for a better and enhanced removal of toxic elements from the contaminated soil with cosmos to be the best amongst these in urban areas.

Post-reclamation microbial diversity and functions in hexachlorocyclohexane (HCH) contaminated soil in relation to spontaneous HCH tolerant vegetation.

The toxicity, volatility and persistence of the obsolete organochlorine pesticide hexachlorocyclohexane (HCH), makes reclamation of contaminated areas a priority for the health and welfare of neighboring human communities. Microbial diversity and functions and their relation to spontaneous vegetation in post-excavation situations, are essential indicators to consider in bioaugmentation or microbe-assisted phytoremediation strategies at field scale. Our study aimed to evaluate the effects of long-term HCH contamination on soil and plant-associated microbial communities, and whether contaminated soil has the potential to act as a bacterial inoculum in post-excavation bioremediation strategies. To scrutinize the role of vegetation, the potential nitrogen fixation of free-living and symbiotic diazotrophs of the legume Lotus tenuis was assessed as a measure of nutrient cycling functions in soil under HCH contamination. Potential nitrogen fixation was generally not affected by HCH, with the exception of lower nifH gene counts in excavated contaminated rhizospheres, most probably a short-term HCH effect on early bacterial succession in this compartment. HCH shaped microbial communities in long-term contaminated bulk soil, where we identified possible HCH tolerants such as Sphingomonas and Altererythrobacter. In L. tenuis rhizosphere, microbial community composition was additionally influenced by plant growth stage. Sphingobium and Massilia were the bacterial genera characteristic for HCH contaminated rhizospheres. Long-term HCH contamination negatively affected L. tenuis growth and development. However, root-associated bacterial community composition was driven solely by plant age, with negligible HCH effect. Results showed that L. tenuis acquired possible HCH tolerant bacteria such as the Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium clade, Sphingomonas, Massilia or Pantoea which could simultaneously offer plant growth promoting (PGP) benefits for the host. Finally, we identified an inoculum with possibly HCH tolerant, PGP bacteria transferred from the contaminated bulk soil to L. tenuis roots through the rhizosphere compartment, consisting of Mesorhizobium loti, Neorhizobium galegae, Novosphingobium lindaniclasticum, Pantoea agglomerans and Lysobacter bugurensis.

Functional potential of sewage sludge digestate microbes to degrade aliphatic hydrocarbons during bioremediation of a petroleum hydrocarbons contaminated soil.

Sewage sludge digestate is a valuable organic waste which can be used as fertilizer in soil bioremediation. Sewage sludge digestate is not only a good source of nutrients but is also rich in bacteria carrying alkB genes, which are involved in aliphatic hydrocarbons metabolism. Increase of alkB genes ratio in polluted soils has been observed to improve bioremediation efficiency. In this study, for the first time, the genetic potential of indigenous microorganisms of digestate to degrade petroleum products was assessed. The objectives were to study petroleum hydrocarbons (PHCs) removal together with shifts in soil taxa and changes in the concentration of alkB genes after digestate application. Initial alkB genes concentration in contaminated soils and digestate was 1.5% and 4.5%, respectively. During soil incubation with digestate, alkB genes percentage increased up to 11.5% and after the addition of bacteria immobilized onto biochar this value increased up to 60%. Application of digestate positively affected soil respiration and bacterial density, which was concomitant with enhanced PHCs degradation. Incubation of soil amended with digestate resulted in 74% PHCs decrease in 2 months, while extra addition of bacteria immobilized onto biochar increased this value up to 95%. The use of digestate affected the microbial community profiles by increasing initial bacterial density and diversity, including taxa containing recognized PHCs degraders. This study reveals the great potential of digestate as a soil amendment which additionally improves the abundance of alkB genes in petroleum contaminated soils.