Chromium toxicity, speciation, and remediation strategies in soil-plant interface: A critical review

In recent decades, environmental pollution with chromium (Cr) has gained significant attention. Although chromium (Cr) can exist in a variety of different oxidation states and is a polyvalent element, only trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)] are found frequently in the natural environment. In the current review, we summarize the biogeochemical procedures that regulate Cr(VI) mobilization, accumulation, bioavailability, toxicity in soils, and probable risks to ecosystem are also highlighted. Plants growing in Cr(VI)-contaminated soils show reduced growth and development with lower agricultural production and quality. Furthermore, Cr(VI) exposure causes oxidative stress due to the production of free radicals which modifies plant morpho-physiological and biochemical processes at tissue and cellular levels. However, plants may develop extensive cellular and physiological defensive mechanisms in response to Cr(VI) toxicity to ensure their survival. To cope with Cr(VI) toxicity, plants either avoid absorbing Cr(VI) from the soil or turn on the detoxifying mechanism, which involves producing antioxidants (both enzymatic and non-enzymatic) for scavenging of reactive oxygen species (ROS). Moreover, this review also highlights recent knowledge of remediation approaches i.e., bioremediation/phytoremediation, or remediation by using microbes exogenous use of organic amendments (biochar, manure, and compost), and nano-remediation supplements, which significantly remediate Cr(VI)-contaminated soil/water and lessen possible health and environmental challenges. Future research needs and knowledge gaps are also covered. The review's observations should aid in the development of creative and useful methods for limiting Cr(VI) bioavailability, toxicity and sustainably managing Cr(VI)-polluted soils/water, by clear understanding of mechanistic basis of Cr(VI) toxicity, signaling pathways, and tolerance mechanisms; hence reducing its hazards to the environment.

Advances in Heavy Metal Bioremediation: An Overview

The pollution of toxic heavy metals is considered one of the most important environmental issues which has accelerated dramatically due to changing industrial activities. This review focuses on the most common methods, strategies, and biological approaches of heavy metal bioremediation. Also, it provides a general overview of the role of microorganisms in the bioremediation of heavy metals in polluted environments. Advanced methods of heavy metal remediation include physicochemical and biological methods; the latter can be further classified into in situ and ex situ bioremediation. The in situ process includes bioventing, biosparging, biostimulation, bioaugmentation, and phytoremediation. Ex situ bioremediation includes land farming, composting, biopiles, and bioreactors. Bioremediation uses naturally occurring microorganisms such as Pseudomonas, Sphingomonas, Rhodococcus, Alcaligenes, and Mycobacterium. Generally, bioremediation is of very less effort, less labor intensive, cheap, ecofriendly, sustainable, and relatively easy to implement. Most of the disadvantages of bioremediation relate to the slowness and time-consumption; furthermore, the products of biodegradation sometimes become more toxic than the original compound. The performance evaluation of bioremediation might be difficult as it has no acceptable endpoint. There is a need for further studies to develop bioremediation technologies in order to find more biological solutions for bioremediation of heavy metal contamination from different environmental systems.

Comparative transcriptome analysis reveals the differential response to cadmium stress of two Pleurotus fungi: Pleurotus cornucopiae and Pleurotus ostreatus

Pleurotus has great potential for heavy metal mycoremediation. Using comparative transcriptome analysis, the response of Pleurotus ostreatus and Pleurotus cornucopiae under Cd contamination was evaluated. P. ostreatus and P. cornucopia accumulated 0.34 and 0.46 mg/g Cd in mycelium, respectively. Cd removal elevated with its concentration elevation, which reached 56.47% and 54.60% for P. ostreatus and P. cornucopia with Cd at 20 mg/L. Low-level Cd (≤ 1 mg/L) had no significant influence on either fungus, while varied response was observed under high-level Cd. 705 differentially expressed genes (DEGs) were identified in P. cornucopia at Cd1 and Cd20, whereas 12,551 DEGs in P. ostreatus. Differentially regulated functional categories and pathways were also identified. ATP-binding cassette transporters were involved in Cd transport in P. cornucopia, whereas the endocytosis and phagosome pathways were more enhanced in P. ostreatus. 26 enzymes including peroxisomal enzymes catalase and superoxide dismutase were upregulated in P. ostreatus, whereas only cytosolic catalase was overexpressed in P. cornucopia, suggesting their different Cd detoxification pathways. Also, the mitogen-activated protein kinase signaling pathway involved in Cd resistance in both species instead of glutathione metabolism, although more active in P. ostreatus. These findings provided new insight into the molecular mechanism of mycoremediation and accumulator screening.

Bioremediation of Waste Water to Remove Heavy Metals Using the Spent Mushroom Substrate of Agaricus bisporus

The presence of heavy metals in waste water brings serious environmental pollution that threatens human health and the ecosystem. Bioremediation of heavy metals has received considerable and growing interest over the years. Thus, this paper presents the use of the Spent Mushroom Substrate (SMS) of Agaricus bisporus cultivation as a bioremediating agent to remove heavy metals that are present in industrial waters. These metals include chromium, lead, iron, cobalt, nickel, manganese, zinc, copper and aluminium. In particular, this study analyses the performance of SMS bioreactors with different groups of heavy metals at various concentrations. Between 80% and 98% of all contaminants that were analysed can be removed with 5 kg of SMS at hydraulic retention times of 10 and 100 days. The best removal efficiencies and longevities were achieved when removing iron (III), nickel and cobalt from contaminated water at a pH of 2.5. These results suggest that SMS can successfully treat waste water that has been contaminated with heavy metals.

Fe3O4 nanoparticle-coated mushroom source biomaterial for Cr(VI) polluted liquid treatment and mechanism research

Agrocybe cylindracea substrate-Fe3O4 (ACS-Fe3O4), a Fe3O4 nanoparticle-coated biomaterial derived from agriculture waste from mushroom cultivation, was developed to remove hexavalent chromium (Cr(VI)) from liquid. After modification, material surface became uneven with polyporous and crinkly structure which improved Cr-accommodation ability in a sound manner. Optimized by the Taguchi method, Cr(VI) removal percentage was up to 73.88 at 240 min, 40°C, pH 3, Cr(VI) concentration 200 mg l-1, dosage 12 g l-1, rpm 200. The efficient Cr(VI) removal was due to the combined effect of adsorption and redox. In addition, verification test using tannery wastewater, with removal percentage of Cr(VI) and total Cr reaching 98.35 and 95.6, provided further evidence for the efficiency and feasibility of ACS-Fe3O4. The effect of storage time of the material on Cr(VI) removal was small, which enhanced its value in practical application. Results indicated that metal removal was mainly influenced by solution concentration, adsorbent dosage and treatment time. The experimental data obtained were successfully fitted with the Langmuir isotherm model. Thermodynamic study indicated the endothermic nature of the process. The results confirmed that ACS-Fe3O4 as novel material derived from waste, with long-term stability, could be applied for heavy metal removal from wastewater and waste cycling.

Self-assembly modified-mushroom nanocomposite for rapid removal of hexavalent chromium from aqueous solution with bubbling fluidized bed

A self-assembled modified Pleurotus Cornucopiae material (SMPM) combined with improved Intermittent Bubbling Fluidized Bed (IBFB) was investigated to remove the hexavalent chromium ions in aqueous solution. After the modification, the powder-like raw material gradually self-assembled together to SMPM, which had crinkly porous structure, improved the Cr-accommodation ability in a sound manner. Optimized by Taguchi method, Cr(VI) removal efficiency was up to 75.91% and 48.01% for 100 mg/L and 500 mg/L initial concentration of Cr(VI), respectively. Results indicated that the metal removal was dependent on dosage of adsorbent, particle diameter and treatment time. The experimental data obtained from the biosorption process was successfully correlated with Freundlich isotherm model. Thermodynamic study indicated the endothermic nature of the process. The results confirmed that self-assembly modified Pleurotus Cornucopiae material could be applied for the removal of heavy metal from wastewater in continuous fluidized bed process.

Packed bed column studies on lead(II) removal from industrial wastewater by modified Agaricus bisporus

Agaricus bisporus showed best performance in removing Pb(II) with a biosorption capacity of 86.4 mg g(-1) after modification with NaOH. In this work, the removal of Pb(II) from wastewater has been conducted in column mode. The metal removal was dependent on the flow rate, initial metal concentration, and bed height. The experimental data obtained from the biosorption process was successfully correlated with the Bohart-Adams, Thomas, and Yoon-Nelson models. Five biosorption-desorption cycles yielded 95.34%, 92.27%, 90.13%, 86.75%, and 81.52% regeneration, respectively. Pb(II) could be effectively removed from industrial wastewater; some metal ions and organics were also removed concomitantly, and the obtained effluent had characteristics of better quality. The results confirmed that modified A. bisporus could be applied for the removal of heavy metals from industrial wastewater in a continuous column process.