Activation of biochar through exoenzymes prompted by earthworms for vermibiochar production: A viable resource recovery option for heavy metal contaminated soils and water

Metal pollution in the topsoil of lands adjacent to Sahiwal Coal Fired Power Plant (SCFPP) in Sahiwal, Pakistan

Coal fly ash from a coal fired power plant is a significant anthropogenic source of various heavy metals in surrounding soils. In this study, heavy metal contamination in topsoil around Sahiwal coal fired power plant (SCFPP) was investigated. Within distance of 0-10, 11-20, 21-30 and 31-40 km of SCFPP, total 56 soil samples were taken, 14 replicate from each distance along with a background subsurface soil sample beyond 60 km. Soil samples were subjected to heavy metals analysis including Fe, Cu and Pb by Atomic Absorption Spectrophotometer (AAS). Composite samples for each distance were analyzed for Al, As, Ba, Cd, Co, Cr, Mn, Mo, Ni, Se, Sr, Zn by Inductively Coupled Plasma (ICP). Pollution indices of exposed soil including Enrichment Factor (EF), Contamination Factor (CF), Geoaccumulation Index (Igeo), and Pollution Load Index (PLI) were calculated. Ecological risk index ([Formula: see text]) of individual metals and the Potential Ecological Risk Index (PERI) for all metals were determined. Soil samples within 40 km of SCFPP were significantly polluted with Pb (mean 2.81 ppm), Cu (mean 0.93 ppm), and Fe (mean 7.93 ppm) compared to their background values (Pb 0.45, Cu 0.3, and Fe 4.9 ppm). Some individual replicates were highly contaminated where Pb, Fe, and Cu values were as high as 6.10, 35.4 and 2.51 ppm respectively. PLI, Igeo, CF, and EF for metals classified the soil around CFPP as "moderate to high degree of pollution", "uncontaminated to moderately contaminated", "moderate to very high contamination", and "moderate to significant enrichment" respectively with average values for Cu as 2.75, 0.82, 3.09, 4.01; Pb 4.79, 1.56, 6.16, 7.76, and for Fe as 1.20, 0.40, 1.62, 3.35 respectively. Average Ecological Risk Index ([Formula: see text]) of each metal and Potential Ecological Risk Index (PERI) for all metals classified the soils as "low risk soils" in all distances. However, ([Formula: see text]) of Pb at a number of sites in all distances have shown "moderate risk". The linear correlation of physico-chemical parameter (EC, pH, Saturation %) and metals have recorded several differential correlations, however, their collective impact on Pb in 0-10 km, has recorded statistically significant correlation (p-value 0.01). This mix of correlations indicates complex interplay of many factors influencing metal concentrations at different sampling sites. The concentration of As, Cr, Co, Cd, and Zn was found within satisfactory limits and lower than in many parts of the world. Although the topsoil around SCFPP is largely recorded at low risk, for complete assessment of its ecological health, further research considering comprehensive environmental parameters, all important trace metals and variety of input pathways is suggested.

Reducing the mass and decreasing the bioavailability of heavy mental from organic wastes treated by black soldier fly larvae

Black soldier fly larvae (BSFL), Hermetia illucens L., are widely used to reduce the mass of various wastes. However, the potential metal tolerance mechanisms during periods of waste bioconversion by BSFL remain largely unknown. To further reveal the mechanisms, BSFL were used to treat the agricultural organic wastes, including pig manure (PM), cow manure (COM), spent mushroom substrate (SMS), and wet distiller grains (WDG). After these individual and combined waste(s) were treated by BSFL, we investigated the waste reduction rates and evaluated the responses of BSFL gut microbes to heavy metals of agricultural organic wastes. Additionally, the colloidal particles of residual wastes were characterized by combing energy dispersive X-ray (EDX) spectroscopy, Size potential, Zeta potential, and excitation-emission matrix (EEM) spectroscopy. Results indicated that the waste reduction rates were up to 74% in COM+WDG and 69% in WDG, most of heavy metals (e.g., Zn and Co) from organic wastes were not accumulated in the bodies of mature larvae after treatment. Further, results obtained from the prediction of gene function on the basis of 16 S rRNA data revealed that the presence of multi-resistance genes in the gut of BSFL can help the larvae resist Zn and/or Co stress. In addition, the drug sensitivity test implied that BSFL5_L and BSFL6_L from BSFL gut bacterial strains have multi-resistance to Co and Zn. Additionally, EDX results revealed that the colloidal particles in five waste residues after BSFL treatment are mainly consisted of Fe, Ca and Si, which can capture heavy metals (e.g., Cu, Mn). Results from EEM spectroscopy and PARAFAC showed that tryptophan-like and humic-like accumulatively account for 56%- 68% of all components. Importantly, these two components could strongly bind the metal elements and form colloidal particles with high stability, and therefore reduce the heavy metal pollution of agricultural organic wastes. Our findings offered an environment-friendly method to treat agricultural organic wastes, which would be far-reaching influence to our environment.

A 50-year systemic review of bioavailability application in Soil environmental criteria and risk assessment

Bioavailability has become a critical factor in improving ecological risk assessment and environmental remediation efficiency in contaminated soil research. However, the soil environmental quality standards and risk assessment procedures used in most countries are still based on the total amount of pollutants for lacking sufficient understanding of the exposure pathways and action mechanisms of pollutants. we collected relevant literature from the Web of Science database, spanning the period from 1950 to 2021 by using Citespace to analyze the scientific development of bioavailability. As of January 09, 2022, the database contained 118,813 publications on bioavailability. The review summarizes the progress in bioavailability research and emerging trends, including exploring advanced analytical techniques, advancing modeling approaches, and integrating interdisciplinary approaches to better understand the fate and behavior of pollutants in complex environmental matrices. In particular, the review emphasizes the need for better integration of bioavailability concepts into soil environmental reference, risk assessment procedures, and environmental remediation strategies. Overall, this review emphasized the necessity of incorporating the concept of bioavailability into soil environmental reference, risk assessment procedures, and environmental remediation strategies.

Biochar preparation and evaluation of its effect in composting mechanism: A review

This article provides an overview of biochar application for organic waste co-composting and its biochemical transformation mechanism. As a composting amendment, biochar work in the adsorption of nutrients, the retention of oxygen and water, and the promotion of electron transfer. These functions serve the micro-organisms (physical support of niche) and determine changes in community structure beyond the succession of composing primary microorganisms. Biochar mediates resistance genes, mobile gene elements, and biochemical metabolic activities of organic matter degrading. The participation of biochar enriched the α-diversity of microbial communities at all stages of composting, and ultimately reflects the high γ-diversity. Finally, easy and convincing biochar preparation methods and characteristic need to be explored, in turn, the mechanism of biochar on composting microbes at the microscopic level can be studied in depth.

Hormesis-tempting stressors driven by evolutionary factors for mitigating negative impacts instigated over extended exposure to chemical elements

The adaptive responses to moderate environmental challenges by the biological systems have usually been credited to hormesis. Since the hormetic biphasic dose-response illustrates a prominent pattern towards biological responsiveness, the studies concerning such aspects will get much more significance in risk assessment practices and toxicological evaluation research. From this point of view, the past few epochs have witnessed the extending recognition of the notion concerning hormesis. The extraction of its basic foundations of evolutionary perspectives-along with the probable underlying molecular and cellular mechanisms followed by the practical implications to enhance the quality of life. To get better and more effective output in this regard, the present article has evaluated the various observations of previous investigations. The intent of integrating the novel inferences concerning the hormesis-tempting stressors driven by predominant evolutionary factors for mitigating the adverse impacts that were prompted over frequent and continuous exposure to the various chemical elements. Such inferences can offer extensive insight into the implications concerning the risk assessment of hormesis.

Activation methods increase biochar's potential for heavy-metal adsorption and environmental remediation: A global meta-analysis

Removal of heavy metals (HMs) by adsorption on biochar's surface has shown promising results in the remediation of contaminated soil and water. The adsorption capacity of biochar can be altered by pre- or post-pyrolysis activation; however, the effect of activation methods on biochar's adsorption capacity varies widely. Here, we conducted a meta-analysis to identify the most effective methods for activation to enhance HM removal by biochar using 321 paired observations from 50 published articles. Activation of biochar significantly improves the adsorption capacity and removal efficiency of HMs by 136 and 80 %, respectively. This study also attempts to find suitable feedstocks, pyrolysis conditions, and physicochemical properties of biochar for maximizing the effect of activation of biochar for HMs adsorption. Activation of agricultural wastes and under pyrolysis temperatures of 350-550 °C produces biochars that are the most effective for HM adsorption. Activation of biochars with a moderate particle size (0.25-0.80 mm), low N/C (<0.01) and H/C ratios (<0.03), and high surface area (> 100 m² g^-1) and pore volume (> 0.1 cm³ g^-1) are the most desirable characteristics for enhancing HM adsorption. We conclude that pre-pyrolysis activation with metal salts/oxides was the most effective method of enhancing biochar's potential for adsorption and removal of a wide range of HMs. The results obtained from this study can be helpful in choosing appropriate methods of activations and the suitable choice of feedstocks and pyrolysis conditions. This will maximize HM adsorption on biochar surfaces, ultimately benefiting the remediation of contaminated environments.

Production and characterization of enriched vermicompost from banana leaf biomass waste activated by biochar integration

Vermicomposting uses less energy and requires fewer infrastructures, and it is capable of restoring soil nutrition and carbon. Banana cultivation produces lots of trash in a single crop season, with 30 tonnes of waste generated per acre. The biodegradable fraction of banana leaf waste is thrown out in large quantities from temples, markets place wedding halls, hotels, and residential areas. Vermicomposting can be used for recovering lignin, cellulose, pectin, and hemicellulose from banana leaves. Earthworm digests organic materials with the enzymes produced in gut microflora. Biochar adds bulk to vermicomposting, increases its value as fertilizer. The goal of this study was to amend biochar (0, 2, 4 and 6%) with banana leaf waste (BLW) + cow dung (CD) in three different combinations (1:1, 2:1 and 3:1) using Eisenia fetida to produce enriched vermicompost. In the vermicompost with biochar groups, there were higher levels of physicochemical parameters, as well as macro- and micronutrient contents. The growth and reproduction of earthworms were higher in groups with biochar. A maximum of 1.82, 1.18 and 1.67% of total nitrogen, total phosphorus and total potassium was found in the final vermicompost recovered from BLW + CD (1:1) amended with 4% biochar; while the other treatments showed lower levels of nutrients. A lower C/N ratio of 18.14 was observed in BLW + CD (1:1) + 4% biochar followed by BLW + CD (1:1) + 2% biochar amendment (19.92). The FTIR and humification index studies show that degradation of organic matter has occurred in the final vermicompost and the substrates with 4% biochar in 1:1 combination showed better degradation and this combination can be used for nutrient rich vermicompost production.

A review on integrated vermifiltration as a sustainable treatment method for wastewater

To overcome the scarcity of fresh water, concerned authorities worldwide are bound to think about remediation and reuse of domestic and industrial effluents. The present review study on integrated vermifiltrationwith hydroponic system explains mechanism followed in system and presently the reutilization and remediation of domestic and industrial effluents. It explains the result of integrated vermifiltration and recognizes factors such as clogging, hydraulic loading rate or rain on bed, salinity, and sunlight affect the efficiency of system. The study also focuses on limitations associated with vermifiltration and also suggestions have been made for enhancing the sustainability and performance of existing practices. After literature review, integrated vermifiltration with hydroponic system considered as a natural and eco-friendly method for treating polluted water. Active zone of vermifilter remove organics, nitrate from nitrogen, total and dissolved phosphorus from wastewater. The vermifiltration and integrated vermifiltration with macrophyte able remove chemical oxygen demand (COD) in the range (53.7%-64.4%) and (75.5%-82.8%) respectively. The integrated system reduces land consumption and wastewater can be reutilized in cultivation.

Evaluation of the treatment performance and reuse potential in agriculture of organized industrial zone (OIZ) wastewater through an innovative vermifiltration approach

Vermifiltration (VF) is a natural and sustainable biofilter that has many advantages, including being energy-free, cost-effective, and allowing ease of application and maintenance. In this study, the effectiveness of a lab-scale VF system was assessed by the removal efficiency of total suspended solids, electrical conductivity, chemical oxygen demand, total nitrogen, total phosphorus, fecal coliform, and heavy metals in organized industrial zones (OIZ) and domestic wastewater (DW) for the first time. Additionally, the reuse suitability of the treated wastewater was determined by comparing different countries' and global irrigational criteria. The lab systems were built with four layers: one worm-bed and three varying filtering materials, and operated at an optimum hydraulic loading rate of 1.8-2 m³/m²/day for 45 days with Eisenia fetida as the earthworm species. The results demonstrated that removal efficiencies of total suspended solids and chemical oxygen demand were found to be 95% and 80% in OIZ wastewater and 90% and 88% in DW, respectively. Total nitrogen and total phosphorus were removed at rates of 69% and 67% in OIZ wastewater, respectively, and 84% and 74% in DW. Besides, the VF system has shown satisfactory removal performance for heavy metals ranging from 51% to 77% in OIZ wastewater that has met Turkish national wastewater discharge limits. Although the final characterization of treated wastewater was suitable, heavy metal and fecal coliform levels have not met many countries' irrigation water quality criteria. To meet global irrigation standards and to enhance the VF performance, further experimental studies should be carried out, including parameters such as bed material type in the reactor, worm type, and different operating conditions.

Toxicity analysis and biomarker response of Quinalphos Organophosphate Insecticide (QOI) on eco-friendly exotic Eudrilus eugeniae earthworm

An ever-increasing use of pesticides in agricultural fields has led to a catastrophic decline in crop quality and, ultimately soil fertility. To control various pests, quinalphos is commonly used in India's tea plantations. This study aims to investigate the effects of the Quinalphos organophosphate insecticide on the non-target beneficial organism Eudrilus eugeniae earthworms and the biomarkers that respond to its effects. Earthworm species, especially E. eugeniae, remains as the most trustworthy and well-suited model organism for conducting a wide variety of environmental studies. The median lethal concentration (LC₅₀) was identified as 3.561 µg cm^-2 (contact filter paper) and 1.054 mg kg^-2 (artificial soil toxicity). The 5% and 10% of LC₅₀ value 3.561 µg cm^-2 was exposed to earthworm to analyze the sublethal effects at pre-clitellum, clitellum, and post-clitellum segments. Specific enzymatic activities of neurotransmitter enzyme acetylcholinesterase; antioxidant enzymes such as lipid peroxidase, superoxide dismutase, and catalase; and detoxification enzymes including glutathione S transferase, reduced glutathione, carboxylesterase, and Cytochrome P450 were analyzed. Exposure of E. eugeniae earthworm to subacute exposures of pesticides caused significant alterations in these stress markers in a concentration-dependent manner. Morphological abnormalities like bulginess, coiling, and bleeding were observed after exposure of the insecticide treatments. Histological cellular disintegration, a reduced NRRT time, and an inhibited proteolytic zone were also identified in pesticide-exposed earthworms. Studies demonstrate that the organophosphate insecticide quinalphos causes acute toxicity in E. eugeniae; hence, it is suggested that non-target eco-friendly E. eugeniae earthworms may be at risk if exposed to the excessive concentrations of quinalphos organophosphate insecticide in soil.

Vermi-cyanobacterial remediation of cadmium-contaminated soil with rice husk biochar: An eco-friendly approach

Present study is aimed to evaluate the influence of earthworm (Eisenia fetida), Cyanobacteria (Cylindrospermum stagnale), and rice husk biochar (BC) on cadmium (Cd) detoxification in artificially contaminated soil. The Cd content was kept at 10 mg/kg in factorial design I, coupled with 2% and 0% BC. E. fetida and C. stagnale un-inoculated and inoculated experiments were maintained respectively as negative and positive controls. In factorial design II, E. fetida and C. stagnale were inoculated, along with BC (0% and 2%, denoted as B), without BC (WB), along with four different Cd concentrations (Cd-0, Cd-5, Cd-10, and Cd-20 mg/kg). Results suggest a substantial amount of Cd removal in BC-assisted treatments when compared to negative control-1. Cd (mg/g) in E. fetida tissue ranged from 0.019 (WB2) to 0.0985 (B4). C. stagnale of WB4 (0.036) bioaccumulated the most Cd (mg/g), while B2 showed the least (0.018). The maximum quantity of metallothionein (5.34 μM/mg) was detected in E. fetida of B4 (factorial design - II) and the minimum was claimed in WB1 (0.48 μM/mg) at the end. Earthworm metallothionein protein is a key component in Cd removal from soil by playing an important role in detoxification process. Microbial communities and humic substances were observed in BC-assisted treatments, which aided in Cd-contaminated soil remediation. The present findings suggest that BC (2%) + earthworms + algae could be a suitable remediation strategy for Cd contaminated soil. BC + earthworm + algal-based investigation on heavy metal remediation will be a valuable platform for detoxifying harmful metals in soils.

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.

Treatment of heavy metal-polluted sewage sludge using biochar amendments and vermistabilization

Heavy metal contamination of sewage sludge hampers its recycling. Contaminated sewage sludge was amended with different proportions of biochar and vermistabilized. Biochar produced from wheat straw was added at four proportions (0%, 2%, 4%, and 6%). Ten earthworms Eisenia fetida were added, and the sludge was vermistabilized for 60 days. Heavy metal and nutrient concentrations and the accumulation of metals to E. fetida were measured. The treatment with 4% biochar was the most efficient in reducing the concentrations of heavy metals. The concentration of Cd decreased 55%, Cr 28%, Cu 30%, and Pb 21%. The concentrations of plant nutrients increased: total N 43%, total P 92%, and total K 60%. E. fetida accumulated all heavy metals in their internal tissues. The survival and reproductive rate of E. fetida improved during the vermistabilization process. We interpret that the biochar alone did not improve the decomposition process, but the main actors were the earthworms E. fetida. The most efficient proportion of biochar was 4%, not the highest tested (6%). We recommend 4% biochar to be used in the vermistabilization of heavy metal-contaminated municipal sewage sludge. The study benefits both the management of heavy metal-contaminated sewage sludge and agriculture where the final vermistabilization product can be used to improve crop production.

Recent trends and advances in composting and vermicomposting technologies: A review

Composting technologies have come a long way, developing from static heaps and windrow composting to smart, artificial intelligence-assisted reactor composting. While in previous years, much attention has been paid to identifying ideal organic waste streams and suitable co-composting candidates, more recent efforts tried to determine novel process-enhancing supplements. These include various single and mixed microbial cultures, additives, bulking agents, or combinations thereof. However, there is still ample need to fine-tune the composting process in order to reduce its impact on the environment and streamline it with circular economy goals. In this review, we highlight recent advances in integrating mathematical modelling, novel supplements, and reactor designs with (vermi-) composting practices and provide an outlook for future developments. These results should serve as reference point to target adjusting screws for process improvement and provide a guideline for waste management officials and stakeholders.

Role of plant growth-promoting rhizobacteria in boosting the phytoremediation of stressed soils: Opportunities, challenges, and prospects

Soil is considered as a vital natural resource equivalent to air and water which supports growth of the plants and provides habitats to microorganisms. Changes in soil properties, productivity, and, inevitably contamination/stress are the result of urbanisation, industrialization, and long-term use of synthetic fertiliser. Therefore, in the recent scenario, reclamation of contaminated/stressed soils has become a potential challenge. Several customized, such as, physical, chemical, and biological technologies have been deployed so far to restore contaminated land. Among them, microbial-assisted phytoremediation is considered as an economical and greener approach. In recent decades, soil microbes have successfully been used to improve plants' ability to tolerate biotic and abiotic stress and strengthen their phytoremediation capacity. Therefore, in this context, the current review work critically explored the microbial assisted phytoremediation mechanisms to restore different types of stressed soil. The role of plant growth-promoting rhizobacteria (PGPR) and their potential mechanisms that foster plants' growth and also enhance phytoremediation capacity are focussed. Finally, this review has emphasized on the application of advanced tools and techniques to effectively characterize potent soil microbial communities and their significance in boosting the phytoremediation process of stressed soils along with prospects for future research.

The Mechanism of Cu2+ Sorption by Rice Straw Biochar and Its Sorption-Desorption Capacity to Cu2+ in Soil

Copper (Cu) pollution in soils has received considerable research attention globally, and biochar has been widely used as an adsorbent for soil pollution of Cu. However, most of the studies focused on the adsorption capacity of biochar, the bioavailability of Cu absorbed by biochar remains unclear. In this work, rice straw biomass was pyrolyzed under oxygen-limited conditions at 400°C (BC400) and 600°C (BC600), their apparent structure, group characteristics, and basic physical and chemical properties were determined. The isothermal and kinetics adsorption of Cu by BC400 and BC600 were analyzed. A pot experiment was used to evaluate the passivation of Cu in the soil by biochar and the bioavailability of Cu adsorbed by biochar in the soil. The smooth surfaces of BC400 evolved into more rough surfaces for BC600, and both types of surfaces may give active sorption sites for Cu, according to SEM pictures. FTIR analysis suggested that BC600 is endowed with more condensed aromatic carbon structures and more available polar functional groups. The adsorption processes of Cu²⁺ by biochar were better fitted Langmuir equation and pseudo-second-order kinetic model. The adsorption isotherms showed monolayer adsorption of Cu²⁺ on biochar. The maximum adsorption capacities of BC600 and BC400 on Cu²⁺ were 43.75 and 30.70 mg g^-1, respectively. Moreover, the pot experiment showed that BC400 and BC600 not only have a strong "passivation" effect on Cu in soil but also prevent the release of adsorbed Cu. Overall, more aromatic carbon structure, more polar functional groups, and higher pH are associated with BC600's increased Cu immobilization ability in soil.

Black soldier fly larvae for organic manure recycling and its potential for a circular bioeconomy: A review

Livestock farming and its products provide a diverse range of benefits for our day-to-day life. However, the ever-increasing demand for farmed animals has raised concerns about waste management and its impact on the environment. Worldwide, cattle produce enormous amounts of manure, which is detrimental to soil properties if poorly managed. Waste management with insect larvae is considered one of the most efficient techniques for resource recovery from manure. In recent years, the use of black soldier fly larvae (BSFL) for resource recovery has emerged as an effective method. Using BSFL has several advantages over traditional methods, as the larvae produce a safe compost and extract trace elements like Cu and Zn. This paper is a comprehensive review of the potential of BSFL for recycling organic wastes from livestock farming, manure bioconversion, parameters affecting the BSFL application on organic farming, and process performance of biomolecule degradation. The last part discusses the economic feasibility, lifecycle assessment, and circular bioeconomy of the BSFL in manure recycling. Moreover, it discusses the future perspectives associated with the application of BSFL. Specifically, this review discusses BSFL cultivation and its impact on the larvae's physiology, gut biochemical physiology, gut microbes and metabolic pathways, nutrient conservation and global warming potential, microbial decomposition of organic nutrients, total and pathogenic microbial dynamics, and recycling of rearing residues as fertilizer.

Effects of further composting black soldier fly larvae manure on toxic metals and resistant bacteria communities by cornstalk amendment

Rapid composting by black soldier fly larvae (BSFL) may be insufficient to maturation and humification of composting and further composting is necessary. The purpose of this study was to explore cornstalk addition on toxic metals (Cu, Zn, Pb and Cd), toxic metals resistance bacterial (TMRB) destiny and their relationship with physicochemical factors during BSFL manure composting. High-throughput sequencing was performed by six treatments, namely T1 to T6, where T1 to T3 were BSFL manures from chicken, pig and dairy manure, respectively, and T4 to T6 were same manures and utilized cornstalk to adjust C/N to 25. The results showed that cornstalk amendment could enhance the toxic metals immobilization rate compared to control treatments in the ultimate product. TMRB indicated that the major potential hosts bacteria were Firmicutes, Bacteroidota, Proteobacteria, Acidobacteriota and Actinobacteriota, and the sum relative abundance were 63.33%, 90.62%, 83.62%, 69.38%, 50.66% and 90.52% in T1 to T6 at the end of composting. Bacteria diversity and heat map revealed composting micro-ecology with additive cornstalk to remarkably effect main resistant bacterial distribution via adjusting environmental factors and potential hosts bacterial. Finally, T5 treatment was able to greatly decrease the TMRB abundance, and improve the ability of composting and ultimate product quality.

Heavy metals contamination and associated health risks in food webs-a review focuses on food safety and environmental sustainability in Bangladesh

Heavy metals occur naturally in very small amounts in living organisms, but exposure to their higher concentrations is hazardous. Heavy metals at hazardous levels are commonly found in foodstuffs of Bangladesh, mainly due to the lack of safety guidelines and poor management of industrial effluents. Several lines of evidence suggest that the level of heavy metals in foodstuffs of Bangladesh is higher than the acceptable limits set by World Health Organization/Food and Agriculture Organization. Literature survey revealed that the sources and transport pathways of heavy metals in the ecosystem and the abundance of heavy metals in the food products of Bangladesh are potential threats to food safety. However, an extensive assessment of the toxicity of heavy metals in food webs is lacking. Although widespread heavy metal contamination in various foodstuffs and environmental matrices have been summarized in some reports, a critical evaluation regarding multi-trophic transfer and the health risk of heavy metal exposure through food chain toxicity in Bangladesh has not been performed. This systematic review critically discussed heavy metal contamination, exposure toxicity, research gaps, existing legislation, and sustainable remediation strategies to enhance Bangladesh's food safety. In particular, this study for the first time explored the potential multi-trophic transfer of heavy metals via food webs in Bangladesh. Furthermore, we recommended a conceptual policy framework to combat heavy metal contaminations in Bangladesh.

Assessing Heavy Metal Contamination Risk in Soil and Water in the Core Water Source Area of the Middle Route of the South-to-North Water Diversion Project, China

The Middle Route Project of China’s South-to-North Water Diversion Project (SNWDP) is a national-level water source protection zone and the ecological safety of its water quality and surrounding soil is of great significance. In this study, heavy metals in the surface water and topsoil in the core water source area were quantitatively analyzed using a geographic information system (GIS) and geostatistical techniques combined with environmental pollution and ecological risk assessment models to determine their environmental contamination levels, ecological risk levels, and spatial distribution patterns. Cd was identified as an essential factor responsible for the overall slight heavy metal pollution in the topsoil layer. Heavy metal contamination in surface water was primarily driven by alert-level concentrations of Hg and was consistently distributed in areas with high concentrations of Hg in the topsoil. Applying the potential ecological risk index (RI) revealed two key results. First, surface water showed no ecological risk. The concentrations of heavy metals in surface water met the goals set by relevant authorities in China. Second, overall, the topsoil was at low ecological risk, with a spatial pattern primarily influenced by Cd and Hg. Some heavy metals might have similar pollution sources and originate from human activities such as industrial activities, mining and smelting, and pesticide and chemical fertilizer applications. The study is important for improving the soil and water ecology in the reservoir area and ensuring the northward diversion of high-quality water. In addition, it provides a sound basis for making decisions about local heavy-metal remediation and treatment projects.