The effect of major cations on the toxicity of cadmium to Folsomia candida in a sand-solution medium analyzed by biotic ligand modeling

Ecological and health risk assessments of heavy metals and their accumulation in a peanut-soil system

Heavy metals pollution is a notable threat to environment and human health. This study evaluated the potential ecological and health risks of heavy metals (Cu, Cr, Cd, Pb, Zn, Ni, and As) and their accumulation in a peanut-soil system based on 34 soil and peanut kernel paired samples across China. Soil As and Cd posed the greatest pollution risk with 47.1% and 17.6% of soil samples exceeding the risk screen levels, respectively, with 26.5% and 20.6% of the soil sites at relatively strong potential ecological risk level, respectively, and with the geo-accumulation levels at several soil sites in the uncontaminated to moderately contaminated categories. About 35.29% and 2.94% of soil sites were moderately and severely polluted based on Nemerow comprehensive pollution index, respectively, and a total of 32.4% of samples were at moderate ecological hazard level based on comprehensive potential ecological risk index values. The Cd, Cr, Ni, and Cu contents exceeded the standard in 11.76, 8.82, 11.76 and 5.88% of the peanut kernel samples, respectively. Soil metals posed more health risks to children than adults in the order As > Ni > Cr > Cu > Pb > Zn > Cd for non-carcinogenic health risks and Ni > Cr ≫ Cd > As > Pb for carcinogenic health risks. The soil As non-cancer risk index for children was greater than the permitted limits at 14 sites, and soil Ni and Cr posed the greatest carcinogenic risk to adults and children at many soil sites. The metals in peanut did not pose a non-carcinogenic risk according to standard. Peanut kernels had strong enrichment ability for Cd with an average bio-concentration factor (BCF) of 1.62. Soil metals contents and significant soil properties accounted for 35-74% of the variation in the BCF values of metals based on empirical prediction models.

Biotic Ligand Modeling for the Effect of Major Cations on the Uptake of Cadmium in Folsomia candida Exposed in a Sand-Solution Medium

Biotic ligand modeling (BLM) approaches are already applied to predict the bioavailability and possible risk of metals in surface water, but need further development for soils. The present study investigated the effect of major cations (Ca2+ , Mg2+ , Na+ , K+ , and H+ ) on cadmium bioaccumulation in the springtail Folsomia candida. To avoid the complexity of real soils and enable control of elemental speciation in the exposure medium, the animals were exposed to different cadmium concentrations in an inert quartz sand-solution medium. Accumulation of cadmium in the animals was measured after 7 days exposure at different cation concentrations. Among the cations, only Ca2+ significantly affected the uptake of cadmium in the springtails. Mg2+ also had higher effects compared with other selected cations. Using a BLM approach, the uptake of cadmium in the animals predicted by taking into account both Ca2+ and Mg2+ activities correlated well with the measured values (R2  = 0.68). The final estimated conditional binding constants for cadmium (log KCd-BL ), Ca (log KCa-BL ), and Mg (log KMg-BL ) of 1.06, 2.14, and 1.23 L/mol, respectively, were in agreement with previously reported values. The match between predicted and measured uptake data confirms the applicability and usefulness of the BLM for predicting the bioavailability of cadmium to springtails and opens the way for its application in soil. Environ Toxicol Chem 2024;00:1-7. © 2024 SETAC.

Extension of a biotic ligand model for predicting the toxicity of neodymium to wheat: The effects of pH, Ca2+ and Mg2

The damage excessive neodymium (Nd) causes to animals and plants should not be underestimated. However, there is little research on the impact of pH and associated ions on the toxicity of Nd. Here, a biotic ligand model (BLM) was expanded to predict the effects of pH and chief anions on the toxic impact of Nd on wheat root elongation in a simulated soil solution. The results suggested that Nd3+ and NdOH2+ were the major ions causing phytotoxicity to wheat roots at pH values of 4.5-7.0. The Nd toxicity decreased as the activities of H+, Ca2+, and Mg2+ increased but not when the activities of K+ and Na+ increased. The results indicated that H+, Ca2+, and Mg2+ competed with Nd for binding sites. An extended BLM was developed to consider the effects of pH, H+, Ca2+, and Mg2+, and the following stability constants were obtained: logKNdBL = 2.51, logKNdOHBL = 3.90, logKHBL = 4.01, logKCaBL = 2.43, and logKMgBL = 2.70. The results demonstrated that the BLM could predict the Nd toxicity well while considering the competition of H+, Ca2+, Mg2+ and the toxic species Nd3+ and NdOH2+ for binding sites.

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.

A new paradigm in the bioremoval of lead, nickel, and cadmium using a cocktail of biosystems: a metagenomic approach

Lead (Pb), nickel (Ni), and cadmium (Cd) are known for its harmful effects on the environment. Microbial community related to soil plays a pivotal role in configuring several properties of the ecosystem. Thus, remediation of such heavy metals using multiple biosystems had shown excellent bioremoval potential. The current study demonstrates the integrated approach of Chrysopogon zizanioides in combination with earthworm Eisenia fetida augmented with VITMSJ3 potent strain for the uptake of metals like Pb, Ni, and Cd from the contaminated soil. For the uptake of heavy metals, Pb, Ni, and Cd with the concentrations of 50, 100, and 150 mg kg^-1 were supplemented in pots with plants and earthworms. C. zizanioides was used for bioremoval due to their massive fibrous root system which can absorb heavy metals. A substantial increase of 70-80% Pb, Ni, and Cd was found for VITMSJ3 augmented setup. A total of 12 earthworms were introduced in each setup and were tested for the toxicity and damages in the various internal structures. Reduction in malondialdehyde (MDA) content was observed in the earthworms with VITMSJ3 strain proving less toxicity and damages. Metagenomic analysis of the soil associated bacterial diversity was assessed by amplifying the V3V4 region of the 16S rRNA gene and the annotations were studied. Firmicutes were found to be the predominant genus with 56.65% abundance in the bioaugmented soil R (60) proving the detoxification of metals in the bioaugmented soil. Our study proved that a synergistic effect of plant and earthworm in association with potent bacterial strain had higher uptake of Pb, Ni, and Cd. Metagenomic analysis revealed the changes in microbial abundance in the soil before and after treatment.

Earthworms as candidates for remediation of potentially toxic elements contaminated soils and mitigating the environmental and human health risks: A review

Global concerns towards potentially toxic elements (PTEs) are steadily increasing due to the significant threats that PTEs pose to human health and environmental quality. This calls for immediate, effective and efficient remediation solutions. Earthworms, the 'ecosystem engineers', can modify and improve soil health and enhance plant productivity. Recently, considerable attention has been paid to the potential of earthworms, alone or combined with other soil organisms and/or soil amendments, to remediate PTEs contaminated soils. However, the use of earthworms in the remediation of PTEs contaminated soil (i.e., vermiremediation) has not been thoroughly reviewed to date. Therefore, this review discusses and provides comprehensive insights into the suitability of earthworms as potential candidates for bioremediation of PTEs contaminated soils and mitigating environmental and human health risks. Specifically, we reviewed and discussed: i) the occurrence and abundance of earthworms in PTEs contaminated soils; ii) the influence of PTEs on earthworm communities in contaminated soils; iii) factors affecting earthworm PTEs accumulation and elimination, and iv) the dynamics and fate of PTEs in earthworm amended soils. The technical feasibility, knowledge gaps, and practical challenges have been worked out and critically discussed. Therefore, this review could provide a reference and guidance for bio-restoration of PTEs contaminated soils and shall also help developing innovative and applicable solutions for controlling PTEs bioavailability for the remediation of contaminated soils and the mitigation of the environment and human risks.

Reveal the metal handling and resistance of earthworm Metaphire californica with different exposure history through toxicokinetic modeling

Toxicokinetic (TK) model provides a new approach to mechanistically elucidate the natural variation of metal handling strategy by adaptive and sensitive earthworm populations. Here, TK model was applied to explore the metal handling and resistance strategy of wild Metaphire californica with different historical exposure history through a 12-day re-exposure and another 12-day elimination incubation. M. californica populations showed different kinetic strategies for non-essential metals (Cd and Pb) and essential metals (Zn and Cu), which were closely related to their exposure history. M. californica from the most serious Cd-contaminated soil showed the fastest kinetic rates of both Cd uptake (K₁ = 0.78 g_soil/g_worm/day) and elimination (K₂ = 0.23 day^-1), and also had the lowest Cd half-life (t_1/2 = 3.01 day), which demonstrated the potential Cd-resistance of wild M. californica from Cd-contaminated soils. Besides, the comparative experiment showed totally different metal kinetics of laboratory Eisenia fetida from field M. californica, suggesting the impacts of distinct exposure history and species-specifical sensitivities. These findings provide a novel approach to identify and quantify resistance using TK model and also imply the risk of overlooking existing exposure background and interspecies extrapolation in eco-toxicological studies and risk assessments.

Comparison Among Test Substrates in Metal Uptake and Toxicity to Folsomia candida and Hordeum vulgare

The main aim of this short review was to assess the effect of test medium on the bioavailability of metals to the soil invertebrate Folsomia candida and the barley plant Hordeum vulgare. Solution-only exposures and sand-solution media were suitable media with control survival of > 80%. Comparing toxicity and accumulation data, LC₅₀ and/or EC₅₀ values as well as internal concentrations of cadmium (Cd) and copper (Cu) were similar in the tests with different porewater composition for springtails and barley plants. Similar results for toxicity and bioaccumulation of Cd and Cu using different test substrates, suggest the importance of physiological handling of the effects by the organisms rather than the influence of test medium composition.

An improved biotic ligand model (BLM) for predicting Co(II)-toxicity to wheat root elongation: The influences of toxic metal speciation and accompanying ions

In order to explore the effects of pH and accompanying ions on divalent cobalt (Co(II)) toxicity to the wheat root elongation, an improved biotic ligand model (BLM) to predict Co(II) toxicity was developed in solution culture. The results showed that the Co(II)-toxicity decreased with the increases of K⁺, Ca²⁺ and Mg²⁺ activities, and the activity of Na⁺ had no impact on the Co(II)-toxicity. High H⁺ activity reduced the Co(II)-toxicity by the competitive effect of H⁺, while low H⁺ activity affected the toxicity by the change in the type of Co(II) in culture medium. Co²⁺ and CoOH⁺ were toxic to wheat root elongation, and Co(OH)₂ was not. On the basis of BLM theory, the conditional equilibrium constants for Co²⁺, CoOH⁺, H⁺, Mg²⁺, Ca²⁺, K⁺ were obtained: logK_CoBL = 4.65, logK_CoOHBL = 6.62, logK_HBL = 4.53, logK_MgBL = 3.65, logK_CaBL = 2.36 and logK_KBL = 2.17. Free Co²⁺ and CoOH⁺, and the competitions of K⁺, Mg²⁺ and Ca²⁺ were suggested to be considered when developing the Co(II)-BLM.