EFFICIENCY OF THE EARTHWORM Eisenia fetida UNDER THE EFFECT OF ORGANIC MATTER FOR BIOREMEDIATION OF SOILS CONTAMINATED WITH CADMIUM AND CHROMIUM

Synergistic Effects of Earthworms and Plants on Chromium Removal from Acidic and Alkaline Soils: Biological Responses and Implications

Soil heavy metal pollution has become one of the major environmental issues of global concern and solving this problem is a major scientific and technological need for today's socio-economic development. Environmentally friendly bioremediation methods are currently the most commonly used for soil heavy metal pollution remediation. Via controlled experiments, the removal characteristics of chromium from contaminated soil were studied using earthworms (Eisenia fetida and Pheretima guillelmi) and plants (ryegrass and maize) at different chromium concentrations (15 mg/kg and 50 mg/kg) in acidic and alkaline soils. The effects of chromium contamination on biomass, chromium bioaccumulation, and earthworm gut microbial communities were also analyzed. The results showed that E. fetida had a relatively stronger ability to remove chromium from acidic and alkaline soil than P. guillelmi, and ryegrass had a significantly better ability to remove chromium from acidic and alkaline soil than maize. The combined use of E. fetida and ryegrass showed the best effect of removing chromium from contaminated soils, wih the highest removal rate (63.23%) in acidic soil at low Cr concentrations. After soil ingestion by earthworms, the content of stable chromium (residual and oxidizable forms) in the soil decreased significantly, while the content of active chromium (acid-extractable and reducible forms) increased significantly, thus promoting the enrichment of chromium in plants. The diversity in gut bacterial communities in earthworms decreased significantly following the ingestion of chromium-polluted soil, and their composition differences were significantly correlated with soil acidity and alkalinity. Bacillales, Chryseobacterium, and Citrobacter may have strong abilities to resist chromium and enhance chromium activity in acidic and alkaline soils. There was also a significant correlation between changes in enzyme activity in earthworms and their gut bacterial communities. The bacterial communities, including Pseudomonas and Verminephrobacter, were closely related to the bioavailability of chromium in soil and the degree of chromium stress in earthworms. This study provides insights into the differences in bioremediation for chromium-contaminated soils with different properties and its biological responses.

Efficacy of cow and buffalo dung on vermiremediation and phytoremediation of heavy metals via Fourier-transform infrared spectroscopy and comet assay

Heavy metal contamination raised significant concerns throughout the world. The current research aimed to evaluate the impact of organic manure (cow dung and buffalo dung) on vermiremediation and phytoremediation and to remediate heavy metals, i.e., cadmium, lead, and chromium, from artificial contaminated soil via both remediation techniques. The impact of livestock manure was evaluated for the first time which could be effective in in situ as well as ex situ studies. Eisenia fetida, Pheretima lignicola, and Spinacia oleracea were used for the remediation process. Results revealed that E. fetida tolerated lead at 280 mg, cadmium at 150 mg, and chromium at 860 mg compared to P. lignicola. The growth and reproduction of E. fetida were efficient in the cow dung manure compared to buffalo dung. Similarly, seed germination and growth of Spinacia oleracea were better in cow dung media compared to buffalo dung. Bioaccumulation factor showed that E. fetida showed a higher accumulation of heavy metals in their tissues when vermi + phytoremediation was jointly applied (9.50 mg/l of Pb, 24.166 of Cd, and 6.695 of Cr). Fourier-transform infrared spectroscopy indicated that heavy metals had no drastic effects on E. fetida and S. oleracea. Similarly, comet assay revealed that heavy metals had no genotoxic effect on the E. fetida and S. oleracea. It was concluded that both E. fetida and S. oleracea are appropriate for heavy metals remediation in cow dung manure.

A meta-analysis-based evaluation of metallic element accumulation in earthworms

The responses of earthworms to excess soil element concentrations are well studied. However, published information on the metallic element accumulation in individuals is controversial. In this paper, the published data on earthworm As, Cd, Cr, Cu, Ni, Pb, and Zn whole body concentrations were evaluated in individuals collected from contaminated and uncontaminated (control) soils, using meta-analyses. The role of soil pH and exposure time as potential influencing factors on metal accumulation was also assessed. Based on the evaluations, the accumulation of each metallic element was significantly (p < 0.05) more intensive in individuals collected from contaminated soils than in ones from control soils, with minor differences in the order of accumulation intensity among the studied metallic elements. Further, major interspecific differences were indicated in the accumulation, with different species being the most intensive accumulators for individual metallic elements. Among the studied metals, Cu concentration in earthworm bodies increased significantly with increasing soil pH. As for the exposure time-dependent accumulation, Pb concentration was found to decrease significantly with time in whole body tissues of earthworms. These results suggested a high variability in metal- and species-specific accumulation-excretion patterns of earthworms, influenced also by other external factors. Based on the results highlighted in this meta-analysis, accumulation schemes raise the need for further analyses involving other additional variables (e.g., soil type, organic matter content, climatic condition) to get a better understanding of element cycle-earthworm relations.

Remediation of noxious wastewater using nanohybrid adsorbent for preventing water pollution

Removal of toxic elements from wastewater effluent has got a lot of attention because of their severe negative effects on human and environmental health. In the past few years, rapid urbanization and industrial activities in developing countries have exacerbated the destruction of the environment. Most of the wastewater effluents are discharged untreated or inadequately treated, which has become a major concern due to its impact on sustainability and the environment. This is imperative to implement, innovative and resourceful wastewater treatment technologies requiring low investment. Among the various treatment technologies, cutting-edge processes in nano-material sciences have recently piqued the interest of scientists. Nanohybrid absorbents have the potential in improving wastewater treatment and increase water supply by utilizing unconventional water resources. Carbon nanotubes, titanium oxide, manganese oxide, activated carbon (AC), magnesium oxide, graphene, ferric oxides, and zinc oxide are examples of nano-adsorbents that are used to eliminate pollutants. This also demonstrated the effective removal of contaminants along with the harmful effects of chemicals, colorants, and metals found in wastewater. The present manuscript examines potential advances in nanotechnology in wastewater treatment for the prevention of water and soil pollution. This systematic review aims to highlight the importance of nanohybrid absorbents treatment technology for wastewater treatment and to explain how nanohybrid absorbents have the potential to revolutionize industrial pollution. There are also other published review articles on this topic but the present review covers an in-depth information on nano-adsorbents and their targeted contaminants.