Biogeochemical behaviour and toxicology of chromium in the soil-water-human nexus: A review

Intrauterine chromium exposure and cognitive developmental delay: The modifying effect of genetic predisposition

There is limited evidence on the effects of intrauterine chromium (Cr) exposure on children's cognitive developmental delay (CDD). Further, little is known about the genetic factors in modifying the association between intrauterine Cr exposure and CDD. The present study involved 2361 mother-child pairs, in which maternal plasma Cr concentrations were assessed, a polygenic risk score for the child was constructed, and the child's cognitive development was evaluated using the Bayley Scales of Infant Development. The risks of CDD conferred by intrauterine Cr exposure in children with different genetic backgrounds were evaluated by logistic regression. The additive interaction between intrauterine Cr exposure and genetic factors was evaluated by calculating the relative excess risk due to interaction (RERI), attributable proportion due to interaction (AP), and synergy index (SI). According to present study, higher intrauterine Cr exposure was significantly associated with increased CDD risk [each unit increase in ln-transformed maternal plasma Cr concentration (ln-Cr): adjusted OR (95 % CI), 1.18 (1.04-1.35); highest vs lowest quartile: adjusted OR (95 % CI), 1.57 (1.10-2.23)]. The dose-response relationship of intrauterine Cr exposure and CDD for children with high genetic risk was more prominent [each unit increased ln-Cr: adjusted OR (95 % CI), 1.36 (1.09-1.70)]. Joint effects between intrauterine Cr exposure and genetic factors were found. Specifically, for high genetic risk carriers, the association between intrauterine Cr exposure and CDD was more evident [highest vs lowest quartile: adjusted OR (95 % CI), 2.33 (1.43-3.80)]. For those children with high intrauterine Cr exposure and high genetic risk, the adjusted AP was 0.39 (95 % CI, 0.07-0.72). Conclusively, intrauterine Cr exposure was a high-risk factor for CDD in children, particularly for those with high genetic risk. Intrauterine Cr exposure and one's adverse genetic background jointly contribute to an increased risk of CDD in children.

In Situ Formed 3,3',5,5'-Tetramethylbenzidine-Cu(I/II) Charge-Transfer Complex Intermediates Promoting Colorimetric Assay of Cr6

Developing a synthesis-free, multifunctional, and effective colorimetric assay system based on 3,3',5,5'-tetramethylbenzidine (TMB) oxidation is attractive yet challenging. Herein, we established a synergetic Cu2+/Cr6+-promoting strategy for TMB-based colorimetric detection of Cr6+. By introducing Cu2+, critical TMB·+···Cu(I/II)···TMB charge transfer complex (TMC) intermediates were in situ formed to reduce the activation energy of TMB oxidation, thereby accelerating Cr6+-mediated TMB oxidation. TMC intermediates also played a pivotal role in H2O2-participated TMB oxidation, clarifying the secondary responsibility of reactive oxygen species frequently caused by Fenton-like reactions. Leveraging the synergetic capacity between Cu2+ and Cr6+ for TMB oxidation, we demonstrated sensitive and specific colorimetric detections for Cr6+ with a limit of detection of 0.006 μM. With its convenient operation and rapid responsiveness, this strategy successfully enabled the practical detection of Cr6+ in real water samples. This work not only enhances the understanding of the internal acceleration mechanism in colorimetric sensing but also provides valuable opportunities to advance synthesis-free detection platforms.

Sources and health risks of heavy metals in kindergarten dust: The role of particle size

Particle size effects significantly impact the concentration and toxicity of heavy metals (HMs) in dust. Nevertheless, the differences in concentrations, sources, and risks of HMs in dust with different particle sizes are unclear. Therefore, guided by the definition of atmospheric particulate matter, dust samples with particle sizes under 1000 μm (DT1000), 100 μm (DT100), and 63 μm (DT63) from Beijing kindergartens were collected. The concentrations of HMs (e.g., Cd, Pb, Zn, Ni, Cr, Ba, Cu, V, Mn, Co, and Ti) in dust samples with different particle sizes were measured. Besides, the differences in HM concentrations, contamination levels, sources, and source-oriented health risks in dust samples of different particle sizes were systematically explored. The results show that the concentrations of Mn, V, Zn, and Cd gradually increase with decreasing dust particle sizes, the concentrations of Ba and Pb show a decreasing trend, and the concentrations of Cr, Cu, Ni, and Co display an increasing and then decreasing trend. The degree of contamination of HMs in dust of different particle sizes varies, with Cd being the most dominant contaminant. Compared with DT1000 and DT63, DT100 is the most polluted. In addition, the sources of HMs in DT1000, DT100, and DT63 become more single with decreasing particle size, which may be mainly due to the particle-size effect inducing the redistribution of HMs in different sources. Notably, the potential health risk is higher in DT100 than in DT1000 and DT63. The highest contribution of industrial sources to the health risk is found in DT100, which is mainly caused by highly toxic chromium (Cr). This work emphasizes the importance of considering particle size in risk assessment and pollution control, which can provide a theoretical basis for precise management of HMs pollution in dust.

Mechanisms and influential factors of soil chromium long-term stability by an accelerated aging system after chemical stabilization

Chemical stabilization is one of the most widely used remediation strategies for chromium (Cr)-contaminated soils by reducing Cr(VI) to Cr(III), and its performance is affected by human and natural processes in a prolonged period, challenging long-term Cr stability. In this work, we established a method for evaluating the long-term effectiveness of remediation of Cr-contaminated soils, and developed an accelerated aging system to simultaneously simulate acid rain leaching and freeze-thaw cycles. The mechanisms and influencing factors of long-term (50-year) change in soil Cr speciation were unravelled after stabilization with Metafix®. Chemical stabilization remarkably decreased the contents of Cr(VI)soil, Crtotal-leach and Cr(VI)leach, among which the removal rate of Cr(VI) in soil was up to 89.70 %, but it also aggravated soil Cr instability. During the accelerated aging process, Crtotal-leach change rates in chemically stabilized soil samples were 0.0462-0.0587 mg/(L·a), and soil Cr became instable after 20-year accelerated aging. The proportion of Cr bound to organic matter and residual Cr increased in soil, and exchangeable Cr decreased. Linear combination fitting results of XANES also showed that Cr(VI) and Cr3+ were transformed into OM-Cr(III), Fh-Cr(III) and CrFeO3 after restoration. During the accelerated aging process, acid rain leaching activated Cr(III) and dissolved Cr(VI), whereas freeze-thaw cycle mainly affected OM-Cr. Chemical stabilization, acid rain leaching and aging time were the major factors influencing the stability of soil Cr, and the freeze-thaw cycle promoted the influence of acid rain leaching. This study provided a new way to explore the long-term effectiveness and instability mechanisms at Cr-contaminated site after chemical stabilization.

Effects of nZVI on the migration and availability of Cr(VI) in soils under simulated acid rain leaching conditions

Hexavalent chromium, Cr(VI), is a ubiquitous toxic metal that can be reduced to Cr(III) by nano-zero-valent iron (nZVI). Finding out effects of continuous rainfall leaching on the Cr(VI) release and availability remains a problem, needing to be addressed. Whether the Cr(VI) reduction by nZVI and continuous rainfall leaching lead to localized heterogeneity in soil is unclear. Therefore, two in situ high-resolution (HR) techniques of the diffusive gradients in thin-films (DGT) and planar optode were combined with ex situ sampling experiments here. Results demonstrate that nZVI decreased Cr(VI) leaching by 5.60-8.50 % compared to control soils. DGT-measured concentrations of Cr(VI), CDGT-Cr(VI), ranged from 7.31 to 19.4 μg L-1 in the control soils, increasing with depth while CDGT-Cr(VI) in nZVI-treated soils (2.41-6.18 μg L-1) decreased or remained stable with depth. However, simulated acid-rain leaching increases CDGT-Cr(VI) by 1.61-fold in nZVI-treated soils, negatively affecting the remediation. DGT measurements in bulk soils using disc devices are better at capturing the change of Cr(VI) availability at different conditions, whereas 2D-HR DGT mappings did not characterize significant mobilization of Cr(VI) at the micro-scale. These findings emphasize the importance of monitoring Cr(VI) release and availability in remediated soil under acid-rain leaching conditions for effective environment management.

Blood chromium and lung function among Chinese young adults: A comprehensive analysis based on epidemiology and metabolomics

Chromium (Cr) exposure is associated with various respiratory system diseases, but there are limited studies investigating its impact on lung function in young adults. The Cr exposure-related metabolomic changes are not well elucidated. This study recruited 608 students from a university in Shandong Province, China in 2019. We used cohort design fitted with linear mixed-effects models to assess the association between blood Cr concentration and lung function. In addition, we performed metabolomic and lipidomic analyses of baseline serum samples (N = 582) using liquid chromatography-mass spectrometry. Two-step statistical analysis (analysis of variance and mixed-linear effect model) was used to evaluate the effect of blood Cr exposure on metabolites. We found that blood Cr was associated with decreased lung function in young adults. Each 2-fold increase in blood Cr concentrations was significantly associated with decreased FEV1 and FVC by 35.26 mL (95 % CI: -60.75, -9.78) and 38.56 mL (95 % CI: -66.60, -10.51), respectively. In the metabolomics analysis, blood Cr exposure was significantly associated with 14 key metabolites. The changed metabolites were mainly enriched in six pathways including lipid metabolism, amino acid metabolism, and cofactor vitamin metabolism. Blood Cr may affect lung function through oxidative stress and inflammation related pathways.

Informal E-waste dismantling activities accelerated the releasing of liquid crystal monomers (LCMs) in Pakistan: Occurrence, distribution, and exposure assessment

Liquid crystal monomers (LCMs) are emerging contaminants characterized by their persistence, bioaccumulation potential, and toxicity. They have been observed in several environmental matrices associated with electronic waste (e-waste) dismantling activities, particularly in China. However, there is currently no information on the pollution caused by LCMs in other developing countries, such as Pakistan. In this study, we collected soil samples (n = 59) from e-waste dismantling areas with different functions in Pakistan for quantification analysis of 52 target LCMs. Thirty out of 52 LCMs were detected in the soil samples, with the concentrations ranging from 2.14 to 191 ng/g (median: 16.3 ng/g), suggesting widespread contamination by these emerging contaminants. Fluorinated LCMs (median: 10.4 ng/g, range: 1.27-116 ng/g) were frequently detected and their levels were significantly (P < 0.05) higher than those of non-fluorinated LCMs (median: 6.11 ng/g, range: not detected (ND)-76.7 ng/g). The concentrations and profiles of the observed LCMs in the soil samples from the four functional areas varied. The informal dismantling of e-waste poses a potential exposure risk to adults and infants, with median estimated daily intake (EDI, ng/kg bw/day) values of 0.0420 and 0.1013, respectively. Calculation of the hazard quotient (HQ) suggested that some LCMs (e.g., ETFMBC (1.374) and EDFPB (1.257)) may pose potential health risks to occupational workers and their families. Considering the widespread contamination and risks associated with LCMs, we strongly recommend enhancing e-waste management and regulation in Pakistan.

Green low-cost synthesis of zero-valent iron nanoparticles from Palm Petiole Extract for Cr(VI) removal from water

One of the hottest research topics over the last decades was the valorization or/and recycling of agro-industrial wastes into different valuable liquid or solid products, which is considered a sustainable and low-cost approach. In this study, we developed zero-valent iron nanoparticles from Palm Petiole Extract (P-NZVI) using a green and straightforward approach. The as-synthesized P-NZVI was used to adsorb Cr(VI) in water. The physico-chemical characterizations of P-NZVI, including the particle size, crystalline structure, surface area, morphology, and functional groups, were investigated via several techniques such as UV-vis spectroscopy, SEM, TEM, XRD, FTIR, AFM, DLS, pHZPC measurement, and BET analysis. The adsorption performance of P-NZVI was studied under different operational parameters, including pollutant concentration, pH, temperature, and adsorbent mass. The adsorption rate was found to be 89.3% within 40 min, corresponding to the adsorption capacity of 44.47 mg/g under the following conditions: initial Cr(VI) concentration of 40 mg/L, pH 5, and a P-NZVI dosage of 1 g/L. It was found that the adsorption pattern follows the Langmuir and the pseudo-second-order kinetic models, indicating a combination of monolayer adsorption and chemisorption mechanisms. The thermodynamic study shows that the adsorption process is endothermic and spontaneous. The reusability of P-NZVI was carried out four times, showing a slight decrease from 89.3 to 87%. These findings highlight that P-NZVI's could be an effective green adsorbent for removing Cr(VI) or other types of toxic pollutants from water.

Rapid Determination of Cr3+ and Mn2+ in Water Using Laser-Induced Breakdown Spectroscopy Combined with Filter Paper Modified with Gold Nanoclusters

Excessive emissions of heavy metals not only cause environmental pollution but also pose a direct threat to human health. Therefore, rapid and accurate detection of heavy metals in the environment is of great significance. Herein, we propose a method based on laser-induced breakdown spectroscopy (LIBS) combined with filter paper modified with bovine serum albumin-protected gold nanoclusters (LIBS-FP-AuNCs) for the rapid and sensitive detection of Cr3+ and Mn2+. The filter paper modified with AuNCs was used to selectively enrich Cr3+ and Mn2+. Combined with the multi-element detection capability of LIBS, this method achieved the simultaneous rapid detection of Cr3+ and Mn2+. Both elements showed linear ranges for concentrations of 10-1000 μg L-1, with limits of detection of 7.5 and 9.0 μg L-1 for Cr3+ and Mn2+, respectively. This method was successfully applied to the determination of Cr3+ and Mn2+ in real water samples, with satisfactory recoveries ranging from 94.6% to 105.1%. This method has potential application in the analysis of heavy metal pollution.

Extracellular bioreduction is the main Cr(VI) detoxification strategy of Bacillus sp. HL1

Bacterium with high Cr(VI) detoxification capability belonged to the genus Bacillus have been largely explored, yet their reduction strategies are still in debate. Cr(VI) removal performance and mechanism of Bacillus sp. HL1 isolated from tailings a site was comprehensively investigated in this study. Approximately 88.31% of 100 mg/L Cr(VI) was continuously removed within 72 h, while it could resist up to 300 mg/L Cr(VI). Metal ions Mn2+ and Cu2+ could effectively improve the Cr(VI) removal performance to 14.41% and 3.41% under the optimal conditions, respectively. Cr(VI) removal performances by subcellular extracts showed that nearly 45.28% of 100 mg/L extracellular Cr(VI) was efficaciously reduced to Cr(III), while only 14.27%, 6.40%, and 2.73% of the cell-free extract, resting cells, and cell debris were reduced, respectively. This suggested that extracellular bioreduction was the primary Cr(VI) detoxification strategy despite a small part of Cr(VI) reduction took place intracellularly. In particular, the reduction products of the intracellular and extracellular compounds significantly differed, with organo-Cr(III) complex outside the cell and crystalline Cr(III) precipitate inside. Such observation was also evidenced by the intracellular black precipitate observed in the TEM image. XRD, XPS, and EPR analysis showed different Cr(III) compositions of intracellular and extracellular products. This study deepens our insights into the different fates of microorganisms that reduce Cr(VI) intracellularly and extracellularly.

Growth-dependent cr(VI) reduction by Alteromonas sp. ORB2 under haloalkaline conditions: toxicity, removal mechanism and effect of heavy metals

Bacterial reduction of hexavalent chromium (VI) to chromium (III) is a sustainable bioremediation approach. However, the Cr(VI) containing wastewaters are often characterized with complex conditions such as high salt, alkaline pH and heavy metals which severely impact the growth and Cr(VI) reduction potential of microorganisms. This study investigated Cr(VI) reduction under complex haloalkaline conditions by an Alteromonas sp. ORB2 isolated from aerobic granular sludge cultivated from the seawater-microbiome. Optimum growth of Alteromonas sp. ORB2 was observed under haloalkaline conditions at 3.5-9.5% NaCl and pH 7-11. The bacterial growth in normal culture conditions (3.5% NaCl; pH 7.6) was not inhibited by 100 mg/l Cr(VI)/ As(V)/ Pb(II), 50 mg/l Cu(II) or 5 mg/l Cd(II). Near complete reduction of 100 mg/l Cr(VI) was achieved within 24 h at 3.5-7.5% NaCl and pH 8-11. Cr(VI) reduction by Alteromonas sp. ORB2 was not inhibited by 100 mg/L As(V), 100 mg/L Pb(II), 50 mg/L Cu(II) or 5 mg/L Cd(II). The bacterial cells grew in the medium with 100 mg/l Cr(VI) contained lower esterase activity and higher reactive oxygen species levels indicating toxicity and oxidative stress. In-spite of toxicity, the cells grew and reduced 100 mg/l Cr(VI) completely within 24 h. Cr(VI) removal from the medium was driven by bacterial reduction to Cr(III) which remained in the complex medium. Cr(VI) reduction was strongly linked to aerobic growth of Alteromonas sp. The Cr(VI) reductase activity of cytosolic protein fraction was pronounced by supplementing with NADPH in vitro assays. This study demonstrated a growth-dependent aerobic Cr(VI) reduction by Alteromonas sp. ORB2 under complex haloalkaline conditions akin to wastewaters.

Effect of riboflavin on redox balance, osmolyte accumulation, methylglyoxal generation and nutrient acquisition in indian squash (Praecitrullus fistulosus L.) under chromium toxicity

The presence of high chromium (Cr) levels induces the buildup of reactive oxygen species (ROS), resulting in hindered plant development. Riboflavin (vitamin B2) is produced by plants, fungi, and microbes. It serves as a precursor to the coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), which play a crucial role in cellular metabolism. The objective of this work was to clarify the underlying mechanisms by which riboflavin alleviates Cr stress in Praecitrullus fistulosus L. Further, the role of riboflavin in growth, ions homeostasis, methylglyoxal detoxification, and antioxidant defense mechanism are not well documented in plants under Cr toxicity. We found greater biomass and minimal production of ROS in plants pretreated with riboflavin under Cr stress. Results manifested a clear abridge in growth, chlorophyll content, and nutrient uptake in Indian squash plants exposed to Cr stress. Findings displayed that Cr stress visibly enhanced oxidative injury reflected as higher malondialdehyde (MDA), hydrogen peroxide (H2O2), superoxide radical (O2•‒), methylglyoxal (MG) levels alongside vivid lipoxygenase activity. Riboflavin strengthened antioxidant system, enhanced osmolyte production and improved membrane integrity. Riboflavin diminished Cr accumulation in aerial parts that led to improved nutrient acquisition. Taken together, riboflavin abridged Cr phytotoxic effects by improving redox balance because plants treated with riboflavin had strong antioxidant system that carried out effective ROS detoxification. Riboflavin protected membrane integrity that, in turn, improved nutrient uptake in plants.

Efficient adsorption of Cr (VI) onto hematite nanoparticles: ANN, ANFIS modelling, isotherm, kinetic, thermodynamic studies and mechanistic insights

Hematite nanoparticles (AF-Fe2O3NPs) were prepared through a simple method utilizing Acacia falcata leaf extract in this investigation. The nanoparticles were extensively characterized to understand their specific properties. FESEM images revealed agglomerated surface morphology, while EDS confirmed the existence of elemental components, including Fe, O, and C. The mesoporous nature of AF-Fe2O3NPs with a pore diameter of 3.77 nm was determined through BET studies. XRD analysis indicated the crystallinity, with lattice parameters characteristic of hematite nanoparticles (a = 0.504 nm and c = 1.381 nm). Superparamagnetic property of the AF-Fe2O3NPs was affirmed from the saturation magnetization (2.98 emu/g) without any hysteresis. Subsequently, AF-Fe2O3NPs were used as adsorbent for the removal of Cr (VI) from aqueous solution. The experimental data were subjected to machine learning (ML) models, specifically ANN and ANFIS, to predict Cr (VI) removal. Both ML models exhibited excellent predictive capabilities, with high R2 values (>0.99) and low error indices such as MSE, RMSE, and MAE. Furthermore, comprehensive kinetic, isotherm, and thermodynamic studies were conducted to gain insights into the behavior and sorption mechanisms of Cr (VI). The Hill model, a statistical physics model, demonstrated an outstanding fit compared to conventional isotherms. It revealed a saturation adsorption potential of 12.91 mg/g at pH 2, 1.5 g/L dose, and a temperature of 30 °C, corroborating physisorption as the dominant mechanism. XPS results confirmed Cr (VI) reduction to Cr (III) through the appearance of specific peaks at 577.18 and 587.08 eV. Thermodynamic investigations established the endothermicity and spontaneity of the adsorption. In summary, the hematite nanoparticles synthesized in this study exhibit promising potential to remove Cr (VI) from aqueous streams, making them a viable option for water treatment applications.

Bridging Component Strategy in Phosphomolybdate-Based Sensors for Electrochemical Determination of Trace Cr(VI)

Rapid and sensitive electrochemical determination of trace carcinogenic Cr(VI) pollutants remains an urgent and important task, which requires the development of active sensing materials. Herein, four cases of reduced phosphomolybdates with formulas of the (H2bib)3[Zn(H2PO4)]2{Mn[P4Mo6O31H7]2}·6H2O (1), (H2bib)2[Na(H2O)]2[Mn(H2O)]2{Mn[P4Mo6O31H6]2}·5H2O (2), (H2bib)3[Mo2(μ2-O)2(H2O)4]2{Ni[P4Mo6O31H2]2}·4H2O (3), and (H2bib)2{Ni[P4Mo6O31H9]2}·9H2O (4) (bib = 4,4'-bis(1-imidazolyl)-biphenyl) were hydrothermally synthesized under the guidance of a bridging component strategy, which function as effective electrochemical sensors to detect trace Cr(VI). The difference of hybrids 1-4 is in the inorganic moiety, in which the reduced phosphomolybdates {M[P4MoV6O31]2} (M{P4Mo6}2) exhibited different arrangements bridged by different cationic components ({Zn(H2PO4)} subunit for 1, [Mn2(H2O)2]4+ dimer for 2, and [MoV2(μ2-O)2(H2O)4]6+ for 3). As a result, hybrids 1 and 3 display noticeable Cr(VI) detection activity with low detection limits of 14.3 nM (1.48 ppb) for 1 and 6.61 nM (0.69 ppb) for 3 and high sensitivities of 97.3 and 95.3 μA·mM-1, respectively, which are much beyond the World Health Organization's detection threshold (0.05 ppm) and superior to those of the contrast samples (inorganic Mn{P4Mo6}2 salt and hybrid 4), even the most reported noble-metal catalysts. This work supplies a prospective pathway to build effective electrochemical sensors based on phosphomolybdates for environmental pollutant treatment.

Assessment of heavy metal distribution and bioaccumulation in soil and plants near coal mining areas: implications for environmental pollution and health risks

Monitoring heavy metals (HMs) across source distance and depth distribution near coal mining sites is essential for preventing environmental pollution and health risks. This study investigated the distribution of selected HMs, cadmium (Cd2+), chromium (Cr2+), copper (Cu2+), manganese (Mn2+), nickel (Ni2+), lead (Pb2+), and zinc (Zn2+), in soil samples collected from ten sites (S-1-S-10) at two different depths (0-15 and 15-30 cm) and distances of 50, 100, and 200 m from a mining source. Additionally, three plant species, Prosopis spp., Justicia spp., and wheat, were collected to assess HM bioavailability and leaf accumulation. Coal mine activities' impact on soil properties and their HM associations were also explored. Results reveal HM concentrations except for Cr2+ exceeding World Health Organization (WHO) limits. In surface soil, Cd2+ (58%), Cu2+ (93%), Mn2+ (68%), Ni2+ (80%), Pb2+ (35%), and Zn2+ (88%) surpassed permissible limits. Subsurface soil also exhibited elevated Cd2+ (53%), Cu2+ (83%), Mn2+ (60%), Ni2+ (80%), Pb2+ (35%), and Zn2+ (77%). Plant species displayed varying HM levels, exceeding permissible limits, with average concentrations of 1.4, 1.34, 1.42, 4.1, 2.74, 2.0, and 1.98 mg kg-1 for Cd2+, Pb2+, Cr2+, Cu2+, Mn2+, Ni2+, and Zn2+, respectively. Bioaccumulation factors were highest in wheat, Prosopis spp., and Justicia spp. Source distance and depth distribution significantly influenced soil pH, electrical conductivity (EC), and soil organic carbon (SOC). Soil pH and EC increased with an increase in soil depth, while SOC decreased. Pearson correlation analysis revealed varying relationships between soil properties and HMs, showing a considerably negative correlation. Concentrations of HMs decreased with increasing depth and distance from mining activities, validated by regression analysis. Findings suggest crops from these soils may pose health risks for consumption.

A comprehensive study on the ecotoxicity of ivermectin to earthworms (Eisenia fetida)

Ivermectin (IVM) is a dewormer commonly utilized in animal farming. Nevertheless, there is a deficiency of research on the bioecotoxicity of IVM in soil. In this study, earthworms were utilized as test animals to investigate the ecotoxicological impacts of IVM. The experiment lasted 28 days and involved adding varied doses of IVM to a culture substrate of soil mixed with cow dung and feeding it to earthworms. The experiment entailed recording earthworm weight, number of earthworm cocoons, histological damage, oxidative stress indicators, and gene expression levels. The analysis results showed that earthworm growth and reproduction were hampered by IVM. Moreover, pathological damage to the earthworms increased with increasing IVM concentration, which caused increased oxidative damage to the earthworms. These findings offer a summary of the impact of IVM on earthworms and a reference point for future research examining the ecological implications of IVM.

The occurrence of "yellowing" phenomenon and its main driving factors after the remediation of chromium (Cr)-contaminated soils: A literature review

Chromium (Cr) is a highly toxic element, which is widely present in environment due to industrial activities. One of most applicable technique to clean up Cr pollution is chemical reduction. However, the Cr(VI) concentration in soil increases again after remediation, and meanwhile the yellow soil would appear, which is commonly called as "yellowing" phenomenon. To date, the reason behind the phenomenon has been disputed for decades. This study aimed to introduce the possible "yellowing" mechanism and the influencing factors based on the extensive literature review. In this work, the concept of "yellowing" phenomenon was explained, and the most potential reasons include the reoxidation of manganese (Mn) oxides and mass transfer were summarized. Based on the reported finding and results, the large area of "yellowing" is likely to be caused by the re-migration of Cr(VI), since it could not sufficiently contact with the reductant under the effects of the mass transfer. In addition, other driving factors also control the occurrence of "yellowing" phenomenon. This review provides valuable reference for the academic peers participating in the Cr-contaminated sites remediation.