Dose-response analysis of diesel fuel phytotoxicity on selected plant species

Cadmium spurred Microcystis aeruginosa to unleash more toxic metabolites

Cyanobacterial harmful algal blooms (cHABs), normally dominated by Microcystis aeruginosa, pose a threat to aquatic ecosystems due to the release of various harmful metabolites. Cadmium (Cd), a heavy metal commonly found in surface water and sediments, often coincides with cHABs in eutrophic lakes. However, the ecotoxicological effects of Cd on M. aeruginosa and the potential for combined toxicity are not yet fully understood. In this study, we determined the effective concentrations of cadmium from 10 % (EC10) to 50 % (EC50) for M. aeruginosa based on cell density inhibition. We then conducted a combined analysis focusing on the impact of a low dose Cd (EC10, 139 μg/L) on the physiological factors, transcriptome and both intracellular and extracellular metabolites of M. aeruginosa. We found that Cd treatment decreased M. aeruginosa chlorophyll a content by 24.5 %, which coincided with the suppression of genes linked to ribosomal and photosynthesis pathways. However, Cd exposure stimulated the synthesis and extracellular release of cellular compounds by enhancing amino acid and carbohydrate metabolism. This led to elevated extracellular levels of amino acids, organic acids, and secondary metabolites - including peptides, lipids, benzenoids, terpenes, sterols, and glycosides - which could serve as potential toxic metabolites of cyanobacteria. These changes were driven by the activation of osmoregulatory mechanisms, antioxidant-related amino acids, and ATP-binding cassette transport and secretion systems. Our research indicated that low Cd concentrations could stimulate the synthesis and release of toxic metabolites and exacerbate cHAB threats in eutrophic lakes, underscoring the importance of addressing multiple stressors in freshwater environments.

Ecological risk threshold for chromium in Chinese soils and its prediction models

The derivation of chromium (Cr) ecological risk thresholds in soils remains limited, despite their importance as measurement standards and indicators for enacting soil protection policies. In this study, toxicity of Cr in soil to different species was tested based on Log-Logistic dose-effect relationship. On this basis, combined with Cr toxicity measurement data in literature, the ecological risk threshold HC5 for protecting 95% species safety in soils with different properties was obtained by fitting species sensitivity distribution curve (SSD). This research collected various Cr toxicological data from Chinese cropland soils, based on 31 different endpoints covering soil fauna, functional indicators of microorganisms, terrestrial plants, etc., sourced from both our laboratory and existing literature. We applied the SSD method to estimate the hazardous concentration of Cr for HC5 and ultimately established a predictive model according to HC5 and different soil properties. As a result, the EC10 (an effective concentration of Cr resulting in 10% suppression of terminal biological activity) based on 7 different soils and 4 endpoints ranged from 16.8 to 148.0 mg kg-1, and the hormesis of Cr induction reached up to 109%. Overall, the toxicity (EC10) to microorganisms was much lower, while it was higher for graminoids. All the toxicity data were corrected through an aging factor with up to 540 days of equilibration before fitting the SSD curves. After that, a prediction model considering HC5 values and soil properties was established as LogHC5 = 3.003LogpH +0.651LogOC +0.013LogCEC - 0.476. The model was well-verified in field experiments, as the actual and predicted values fell within a 2-fold error range. This approach offers a rigorous scientific foundation for determining the Cr ecological risk threshold and could be important for the conservation of ecological species in soils.

Metagenomic analyses of a consortium for the bioremediation of hydrocarbons polluted soils

A bacterial consortium was isolated from a soil in Noblejas (Toledo, Spain) with a long history of mixed hydrocarbons pollution, by enrichment cultivation. Serial cultures of hydrocarbons polluted soil samples were grown in a minimal medium using diesel (1 mL/L) as the sole carbon and energy source. The bacterial composition of the Noblejas Consortium (NC) was determined by sequencing 16S rRNA gene amplicon libraries. The consortium contained around 50 amplicon sequence variants (ASVs) and the major populations belonged to the genera Pseudomonas, Enterobacter, Delftia, Stenotrophomonas, Achromobacter, Acinetobacter, Novosphingobium, Allorhizobium-Neorhizobium-Rhizobium, Ochrobactrum and Luteibacter. All other genera were below 1%. Metagenomic analysis of NC has shown a high abundance of genes encoding enzymes implicated in aliphatic and (poly) aromatic hydrocarbons degradation, and almost all pathways for hydrocarbon degradation are represented. Metagenomic analysis has also allowed the construction of metagenome assembled genomes (MAGs) for the major players of NC. Metatranscriptomic analysis has shown that several of the ASVs are implicated in hydrocarbon degradation, being Pseudomonas, Acinetobacter and Delftia the most active populations.

Updating risk remediation-endpoints for petroleum-contaminated soils? A case study in the Ecuadorian Amazon region

In Ecuador, the regulatory framework for the remediation of petroleum-contaminated soils is based on predefined concentration endpoints for a selected range of petroleum hydrocarbon compounds. However, such approach may lead to over or under-estimation of the environmental risk posed by contaminated soils. In this study, the end-point remediation criteria according to Ecuadorian Environmental legislation were evaluated using different approaches. The first one was based on Total Extractable Petroleum Hydrocarbons (TEPH) and the second one on Total Bioavailable Petroleum Hydrocarbons (TBPH). Both were compared with ecotoxicological determinations using EC50 -Microtox® bioassay at 5 and 15 min of exposure. The correlation (R2) between EC50 values vs TEPH was of 0.2 and 0.25 for 5 and 15 min, respectively. Meanwhile, R2 between EC50 and TBPH was of 0.9 and 0.65 for 5 and 15 min, respectively, demonstrating a stronger correlation. Our results suggest that a contaminated site where the concentration of the TEPH is higher than the relevant regulatory concentrations may be deemed to present an acceptable risk even though their concentrations exceed the target values in soils. The results also challenge the notion that hormesis is associated with TEPH, contrary to some literature. This study is the first in Ecuador to propose incorporating bioavailability into environmental regulations, highlighting the need for further research to establish realistic and achievable remediation goals based on toxicity studies involving various trophic levels.

Heavy fuel oil-contaminated soil remediation by individual and bioaugmentation-assisted phytoremediation with Medicago sativa and with cold plasma-treated M. sativa

Developing an optimal environmentally friendly bioremediation strategy for petroleum products is of high interest. This study investigated heavy fuel oil (HFO)-contaminated soil (4 and 6 g kg-1) remediation by individual and combined bioaugmentation-assisted phytoremediation with alfalfa (Medicago sativa L.) and with cold plasma (CP)-treated M. sativa. After 14 weeks of remediation, HFO removal efficiency was in the range between 61 and 80% depending on HFO concentration and remediation technique. Natural attenuation had the lowest HFO removal rate. As demonstrated by growth rate and biomass acquisition, M. sativa showed good tolerance to HFO contamination. Cultivation of M. sativa enhanced HFO degradation and soil quality improvement. Bioaugmentation-assisted phytoremediation was up to 18% more efficient in HFO removal through alleviated HFO stress to plants, stimulated plant growth, and biomass acquisition. Cold plasma seed treatment enhanced HFO removal by M. sativa at low HFO contamination and in combination with bioaugmentation it resulted in up to 14% better HFO removal compared to remediation with CP non-treated and non-bioaugmented M. sativa. Our results show that the combination of different remediation techniques is an effective soil rehabilitation strategy to remove HFO and improve soil quality. CP plant seed treatment could be a promising option in soil clean-up and valorization.

Elucidating the significant roles of root exudates in organic pollutant biotransformation within the rhizosphere

Biotransformation of organic pollutants is crucial for the dissipation of environmental pollutants. While the roles of microorganisms have been extensively studied, the significant contribution of various root exudates are still not very well understood. Through plant growth experiment, coupled with gas and liquid chromatography-mass spectrometry methods, this study examined the effect of the presence of M. sativa on microbial-associated biochemical transformation of petroleum hydrocarbons. The results of this study revealed that the concentration of exudates within the soil matrix is a function of proximity to root surfaces. Similarly, biodegradation was found to correlate with distance from roots, ranging from ≥ 90% within the rhizosphere to < 50% in bulk soil and unplanted control soil. Most importantly, for the first time in a study of an entire petroleum distillate, this study revealed a statistically significant negative correlation between root exudate concentration and residual total petroleum hydrocarbons. While not all the compounds that may influence biodegradation are derived from roots, the results of this study show that the presence of plant can significantly influence biodegradation of hydrocarbon pollutants through such root exudation as organic acids, amino acids, soluble sugars and terpenoids. Therefore, root exudates, including secondary metabolites, offer great prospects for biotechnological applications in the remediation of organic pollutants, including recalcitrant ones.

Environmental risk thresholds and prediction models of Cd in Chinese agricultural soils

Soil environmental risk threshold of cadmium (Cd) is an important index in formulating soil protection policy. Environmental risk threshold refers to the maximal allowable critical concentration of hazardous substances in the environment. Although there is less study on how to determine soil Cd environmental risk threshold, it is a crucial indicator in formulating soil conservation policies and a key factor in assessing soil environmental quality. The main research content of the study is deducing the environmental risk threshold, aiming to provide scientific basis for the study of environmental quality standards of agricultural land and provide technical support for the protection of Cd pollution of agricultural land. The hazard concentration of 5 % species (HC5, which protects 95 % of species) was determined here using different toxicological data of Cd from 23 test endpoints, interspecific extrapolation using the species sensitivity distribution (SSD) method, and a prediction model was created on the basis of several soil parameters. According to the findings, Cd effective concentration (EC10) (Cd concentration which blocks 10 % of an endpoint's bioactivity) varied from 0.109 to 221 mg·kg-1, and the hormetic response induced by Cd reached 118 % displaying in the dose-response curve of Lolium perenne L.. Toxicology data was rectified by the aging factor considering biogeochemical processes of the newly added pollutants prior to SSD curves fitting. After that, the prediction model was created with the equation of LogHC5 = 0.147 pH + 0.067 OC -1.616. The field test properly validated the prediction model, demonstrating its ability to forecast Cd toxicity levels for various soil conditions. This study offers a scientifically sound methodology for determining the environmental risk limitation for Cd and identifies critical paths for the preservation of environmental species.

Ecological risk threshold for Pb in Chinese soils

Derivation of ecological risk threshold (the threshold concentration value that protect a certain proportion of species within the acceptable hazard level) of lead (Pb) is a yardstick and plays a key role in formulating soil protection policies, while the research about deducing soil Pb ecological risk threshold is still limited. In this study, toxicological data of Pb based on 30 different test endpoints was collected from our experiment and literature, and applied into interspecific extrapolation by species sensitivity distribution (SSD) method to derive the hazard concentration for 5% of species (HC₅, that can protect 95% of species), the prediction models according to different soil properties were established. The results showed that EC₁₀ (the effective concentrations of Pb that inhibit 10% of endpoint bioactivity) ranged from 205.6 to 1596.3 mg kg¹, and hormesis induced by Pb were up to 118%. Toxicity data were corrected by leaching and aging process before SSD curves fitting. HC₅ was then derived and prediction model was developed, as LogHC₅ = 0.134 pH + 0.315 LogOC + 0.324 LogCEC + 1.077. The prediction model was well verified in the field test, indicating that can correctly estimate Pb ecotoxicity thresholds in different soils. This study provides a scientific frame for deriving the ecological risk threshold of Pb and is of great significance for ecological species protection.

Biostimulation of Petroleum-Contaminated Soil Using Organic and Inorganic Amendments

The most common approaches for the in-situ bioremediation of contaminated sites worldwide are bioaugmentation and biostimulation. Biostimulation has often proved more effective for chronically contaminated sites. This study examined the effectiveness of optimized water hyacinth compost in comparison with other organic and inorganic amendments for the remediation of crude oil-polluted soils. Water hyacinth was found to be rich in nutrients necessary to stimulate microbial growth and activity. An organic geochemical analysis revealed that all amendments in this study increased total petroleum hydrocarbon (TPH) biodegradation by ≥75% within 56 days, with the greatest biodegradation (93%) occurring in sterilized soil inoculated with optimized water hyacinth compost. This was followed by polluted soil amended with a combination of spent mushroom and water hyacinth composts (SMC + WH), which recorded a TPH biodegradation of 89%. Soil amendment using the inorganic fertilizer NPK (20:10:10) resulted in 86% TPH biodegradation. On the other hand, control samples (natural attenuation) recorded only 4% degradation. A molecular analysis of residual polycyclic aromatic hydrocarbons (PAHs) showed that the 16 PAHs designated by the US EPA as priority pollutants were either completely or highly degraded in the combined treatment (SMC + WH), indicating the potential of this amendment for the environmental remediation of soils contaminated with recalcitrant organic pollutants.

Ecological toxicity (ECx) of Pb and its prediction models in Chinese soils with different physiochemical properties

The lack of toxicological data becomes the main bottleneck of ecological risk assessment of lead (Pb) in Chinese soils. The present study assessed Pb toxicity on three underground test endpoints (barley root elongation, earthworm avoidance response, and substrate-induced respiration (SIR) of microorganism) in 10 different soils. Hormetic dose-response induced by Pb was >118 % for earthworm avoidance response. EC₁₀ and EC₅₀ (the effective concentrations of Pb that inhibit 10 % or 50 % of endpoint bioactivity and also represents the toxicity threshold of Pb) after leaching increased by 0.32-8.73 times, and 1.02-3.75 times, respectively. Leaching factor (LF) prediction models indicated pH and cation exchange capacity (CEC) were the vital predictors for LF₁₀ and LF₅₀, explaining 60.6 % and 73.1 % of variations, respectively. SIR was one sensitive test endpoint for Pb toxicity, with the lowest of EC₁₀ and EC₅₀ values (from 373.7 to 1008.5 mg·kg^-1, and from 837.1 to 2869.0 mg·kg^-1, respectively). The best prediction models between EC_x and soil properties is LogEC₅₀ = 1.324Log(pH) + 0.423Log(CEC) + 1.742 (R² = 0.761, p < 0.01). The results displayed significant implications for deriving EC_x of Pb, and provided a scientific basis for soil ecological risk assessment of Pb.

Aging factor and its prediction models of chromium ecotoxicity in soils with various properties

Aging of pollutants determines bioavailability and toxicity thresholds of environmental pollutants in soil. However, the ecotoxicity of chromium (Cr) rarely considers the effect of aging as well as soil properties. In order to explore the aging characteristics and establish their quantitative relationship with different soil properties, this study selected 7 soils with different properties through exogenous addition of Cr and determined its toxicity on barley root elongation. From 14d to 540d, EC₁₀ and EC₅₀ of barley root elongation ranged from 21.40 to 312.52 (mg·kg^-1) and 50.15 to 883.88 (mg·kg^-1) respectively. The hormesis appeared in the dose-response curve of acid soil as relative barley root elongation reached >110 % compared with the control. Extended aging time of Cr from 14d to 540d was associated with the attenuation of the toxicity of Cr, as the aging factor increased from 1.26 to 6.09 for EC₅₀, from 0.88 to 4.98 for EC₁₀. The prediction model of AF_EC50 and soil properties is lg (AF_360d) = 0.306lg Clay+0.026lg CEC + 0.240 (R² = 0.872, P < 0.01). The results demonstrated that with the extension of aging time, the toxicity of Cr decreased at 360d and reached a slow reaction stage, after that soil OC, Clay and CEC could well explain the aging procedure of Cr (VI). These results are beneficial for risk assessment of Cr contaminated soils and establishment of a soil environmental quality criteria for Cr.

Assessment of the toxicity of weathered petroleum hydrocarbon impacted soils to native plants from a site in the Canadian Subarctic

Remedial guidelines for petroleum hydrocarbons (PHCs) in soil aid in the mitigation of risks to human health and the environmental. However, some remediation guidelines may overestimate the potential for adverse effects to native plant species, contributing to unnecessary remedial efforts in attempts to meet the guidelines. At sites where PHC-contaminated soils undergo weathering, some PHCs may persist but with decreased bioavailability to organisms. In this study, the toxicity of both coarse and fine-grained subarctic soils, contaminated with weathered PHCs were assessed using five native plant species (Picea mariana, Achillea millefolium, Alnus viridis, Elymus trachycaulus and Salix bebbiana). Soil toxicity tests were conducted in a growth chamber with parameters set to simulate the site's subarctic climate conditions. Reference toxicant tests using boric acid were conducted to provide confidence in the interpretation of the results for the PHC-contaminated soils, and also provide new information on the sensitivities of the four boreal species to boric acid. All plants exhibited reduced growth and germination rates as boric acid concentrations increased. Despite exceeding the Canada-wide standard guidelines for Fraction 3 PHCs, field-collected contaminated soils had no significant negative impacts on the growth (i.e., length, dry weight and emergence) of any of the plant species tested.

Phytotoxicity complements chemical assessment for re-use and re-purposing of refinery wastes for soil amendment purposes after bioremediation

The objective of this study was to assess the suitability of onsite re-use of mature compost for landscaping and tree mulching, produced from the bioremediation of oily sludge from the refinery. Compost samples from the co-composting process were analysed for a range of contaminants, including a human health risk assessment fractionation (HRAF) of the remaining petroleum hydrocarbons, as well as a phytotoxicity test. The chemical characterisation demonstrated that the process removed more than 94% of the original petroleum hydrocarbons from the sludge, and the removal rates were high at 1155 mg/kg/day. The HRAF demonstrated no residual risks, posed by the petroleum hydrocarbons present in the compost to human health if used on-site when compared to the relevant Australian environmental investigation levels (ILs). However, the phytotoxicity assessment demonstrated that the compost was toxic to germinating lettuce. The gap in the literature this study addressed was to provide an estimate of the LD₅₀ and no effect concentration (NEC) for the compost using a standard plant bioassay containing a range of residual (aged) and bioremediated refinery process wastes, including petroleum hydrocarbons. The values estimated for LD₅₀ and NEC were approximately 125 and 43 mg/kg, respectively for compost containing residual petroleum hydrocarbon fractions, filling a gap in the current literature which has limited data on standard toxicity values that can be used in determining and informing commercial remediation strategies and their outcomes with aged sludges. Phytotoxicity was shown to be an important complement to conventional analyses and HRAF data when characterising the sludge, and understanding its potential for re-use. The novelty of the study is that it highlighted a gap in the complementary use of chemical and bioassay analyses for evaluating refinery waste remediation endpoints, which has potential for broader application to other projects.

Influence of toxic diesel fuel on Petunia grandiflora calli and after plant regeneration

The toxic effects of diesel fuel on whole plants have been reported before, but little is known about the toxic effect of diesel fuel on callus cultures. This knowledge is a pre-requisite for exploring the possibility of using a sub-lethal diesel concentration as an agent for in vitro cell line selection to obtain novel somaclonal variants resistant to diesel toxicity. These novel variants could be useful for the phytoremediation of diesel-contaminated soil. Here, a callus induction medium [Murashige and Skoog medium supplemented with 1.8 µM of naphthlene-1-acetic acid (NAA) and 6.6 µM of 6-benzyladenine (BA)] was found to induce 85% of Petunia grandiflora leaf explants to form light green calli. Since it was not possible to include diesel in aseptic culture, the P. grandiflora calli were exposed to diesel under non-aseptic conditions. It was found that the calli did not exhibit any sign of necrosis immediately after up to 9 min of diesel exposure. The diesel-treated calli were subsequently subcultured successfully on the callus induction medium using the proliferating, non-necrotic cells. Transverse sections of the control and diesel-treated calli after 2 weeks of culture revealed that the control calli exhibited more small meristematic cells while diesel-treated calli exhibited larger, empty-looking parenchyma cells. Moreover, it was possible to induce, though at a low frequency (< 15%), shoot formation in the control calli and those derived from the diesel treatment on the Murashige and Skoog medium supplemented with 1.1 µM of indole-3-acetic acid (IAA) and 13.3 µM of BA. Under glasshouse conditions, the shoots regenerated from the calli derived from the diesel treatment exhibited higher biomass than those from the control calli and P. grandiflora seedlings when grown in a potting mix spiked with 0%, 2% and 7% diesel. Taken together, these results suggest that up to 9 min of diesel exposure of P. grandiflora calli was sub-lethal.

Long-term nickel contamination increased soil fungal diversity and altered fungal community structure and co-occurrence patterns in agricultural soils

Nickel (Ni) contamination imposes deleterious effects on the stability of soil ecosystem. Soil fungal community as a crucial moderator of soil remediation and biochemical processes has attracted more and more research interests. In the present study, soil fungal community composition and diversity under long-term Ni contamination were investigated and fungal interaction networks were built to reveal fungal co-occurrence patterns. The results showed that moderate Ni contamination significantly increased fungal diversity and altered fungal community structure. Functional predictions based on FUNGuild suggested that the relative abundance of arbuscular mycorrhizal fungi (AMF) significantly increased at moderate Ni contamination level. Ni contamination strengthened fungal interactions. Keystone taxa at different Ni contamination levels, such as Penicillium at light contamination, were identified, which might have ecological significance in maintaining the stability of fungal community to Ni stress. The present study provided a deeper insight into the effect of long-term Ni contamination on fungal community composition and co-occurrence patterns, and was helpful to further explore ecological risk of Ni contamination in cultivated field.

Ecological risk thresholds for Zn in Chinese soils

The environmental risk threshold of a pollutant is a yardstick to measure soil environmental quality. The derivation of ecological risk thresholds of the heavy metal zinc (Zn) in soil environments based on up-to-date ecological risk assessments plays an important role in soil protection policy. According to regional soil classification, different representative soils with various degrees of acidity and alkalinity were selected, and a data set comprising ecotoxicities of Zn to 21 different test endpoints (plants, soil fauna, microorganisms, etc.) found in representative farmland soils of China was compiled based on new and published data to determine toxicological limits of Zn effects on endpoints. These limits were derived from fitted dose-response model parameters and indicated by EC₁₀ values (the effective concentrations of Zn that inhibit 10% of endpoint bioactivity and also represents the toxicity threshold of Zn in this study) ranging from 36 mg·kg^-1 to 682 mg·kg^-1. The hormesis effect appeared in the dose-response curve of Zn, for example, the relative Chinese cabbage growth reached more than 120% at most. Zn concentrations added in toxicity tests were also corrected for aging and leaching effects in order to more accurately reflect field conditions. The hazardous concentrations for 5% of the species affected (HC₅) were derived by the species sensitivity distribution (SSD) approach for four major types of Chinese soils: acidic (38 mg·kg^-1), neutral (106 mg·kg^-1), alkaline (217 mg·kg^-1), and alkaline calcareous soils (155 mg·kg^-1). Prediction models of ecological risk thresholds for Zn based on soil properties were generated, such as logHC₅ = 0.564 + 0.218pH + 0.097OC (R² = 0.790,p < 0.001). The predicted models based on lab test data were verified in the field, and the measured field data fell within two-fold of the prediction intervals. This work provides a scientific framework for developing soil-specific guidance on Zn toxicity thresholds.

In Silico Conformation of the Drug Colchicine into Tubulin Models and Acute Phytotoxic Activity on Cucumis sativus Radicles

Many tests are used to determine the toxic activity of miscellaneous substances, and those that are simple, fast, and inexpensive are useful for screening compounds with applications in different fields. The Cucumis sativus root growth inhibition test is an example of acute toxicity determinations. On the other hand, colchicine has been used as a herbicide to generate polyploids in plant species finally reaching the environment; for this reason, colchicine could become a point of attention in ecotoxicology. This work established that Cucumis sativus, at the colchicine binding site (CBS) in tubulin, shares 100% similarity with humans. Colchicine was docked on seven Cucumis sativus computational models of the αβ-tubulin heterodimer, allowing us to understand a possible conformation in tubulin to trigger its antimitotic effect. Furthermore, an in vitro phytotoxicity assay of colchicine-treated cucumber radicles indicated a hormetic-type concentration-dependent response with macroscopic changes in radicles and hypocotyl. These results support the highly preserved grade of tubulins in several species, and using microtubule inhibitors could require attention in ecotoxicological issues. The Cucumis sativus root growth test could help evaluate small molecules (colchicine analogs), chiefly by CBS interactions, a known druggable site, still a target in the search for antimitotic compounds.

Hydrochar and hydrochar co-compost from OFMSW digestate for soil application: 2. agro-environmental properties

The work concerns the study of the hydrochar from digestate and hydrochar co-compost characterization as amendments. The processes for hydrochar and co-compost production were described in Part 1 of this work (Scrinzi et al., 2022). The amendment properties of hydrochar (produced at 180-200-220 °C for 3 h) and co-composts (25%, 50%, and 75% hydrochar percentage of digestate substitution) were assessed by phytotoxicity, plant growth bioassay, and soil effect. Different seeds species (Lepidium sativum, Cucumis sativus, and Sorghum bicolor sp.) were dosed at increased concentrations using both wet raw amendments and their water extracts. The chemical characterization showed phytotoxic compounds content depending on both the initial feedstock (digestate) and the HTC process; at the same time, the analysis highlighted the reduction of these compounds by composting (organic acid, polyphenols, salt concentration). The dose-response was analyzed by the Cedergreen-Streibig-Ritz model and the half-maximal effective concentration (EC50) was calculated based on this equation. The soil properties and GHG emissions measurements (CH₄, CO₂, N₂O, and NH₃) highlighted the effect on N dynamics and on soil respiration induced by substrates. The HC200 soil application determined a significant impact on CO₂ and N₂O emission and NH₃ volatilization (10.82 mol CO₂/m²; 51.45 mmol N₂O/m²; 112 mol NH₃/m²) and a significant reduction of total N and TOC (46% of TKN and 49% of TOC). The co-compost (75%) showed specific effects after soil application compared to other samples an increase of available P (48%), a greater content of nitrogen (1626 mg/kg dry basis), and a reduction of organic carbon (17%). Our results demonstrate the good quality of co-compost and at the same time the validity of this post-treatment for addressing many issues related to hydrochar use in the soil as an amendment, confirming the suitability of HTC process integration for digestate treatment in anaerobic digestion plants.

Hormesis induced by silver iodide, hydrocarbons, microplastics, pesticides, and pharmaceuticals: Implications for agroforestry ecosystems health

Increasing amounts of silver iodide (AgI) in the environment are expected because of the recent massive expansion of weather modification programs. Concurrently, pharmaceuticals, microplastics, hydrocarbons, and pesticides in terrestrial ecosystems continue contaminating forests and agroforests. Our review supports that AgI induces hormesis, a biphasic dose response characterized by often beneficial low-dose responses and toxic high-dose effects, which adds to the evidence for pharmaceuticals, microplastics, hydrocarbons, and pesticides induced hormesis in numerous species. Doses smaller than the no-observed-adverse-effect-level (NOAEL) positively affect defense physiology, growth, biomass, yields, survival, lifespan, and reproduction. They also lead to negative or undesirable outcomes, including stimulation of pathogenic microbes, pest insects, and weeds with enhanced resistance to drugs and potential negative multi- or trans-generational effects. Such sub-NOAEL effects perplex terrestrial ecosystems managements and may compromise combating outbreaks of disease vectors that can threaten not only forest and agroforestry health but also sensitive human subpopulations living in remote forested areas.

QSAR models for soil ecotoxicity: Development and validation of models to predict reproductive toxicity of organic chemicals in the collembola Folsomia candida

Soil pollution is a critical environmental challenge: the substances released in the soil can adversely affect humans and the ecosystem. Several bioassays were developed to investigate the soil ecotoxicity of chemicals with soil microbes, plants, invertebrates and vertebrates. The 28-day collembolan reproduction test with the springtail Folsomia candida is a recently introduced bioassay described by OECD guideline 232. Although the importance of springtails for maintaining soil quality, toxicity data for Collembola are still limited. We have developed two QSAR models for the prediction of reproductive toxicity induced by organic compounds in Folsomia candida using 28 days NOEC data. We assembled a dataset with the highest number of compounds available so far: 54 compounds were collected from publicly available sources, including plant protection products, reactive intermediates and industrial chemicals, household and cosmetic ingredients, drugs, environmental transformation products and polycyclic aromatic hydrocarbons. The models were developed using partial least squares regression (PLS) and the Monte Carlo technique with respectively the open source tools Small Dataset Modeler and CORAL software. Both QSAR models gave good predictive performance even though based on a small dataset, so they could serve for the ecological risk assessment of chemicals for terrestrial organisms.

Structure and diversity of fungal communities in long-term copper-contaminated agricultural soil

Copper (Cu) contamination threatens the stability of soil ecosystems. As important moderators of biochemical processes and soil remediation, the fungal community in contaminated soils has attracted much research interest. In this study, soil fungal diversity and community composition under long-term Cu contamination were investigated based on high-throughput sequencing. The co-occurrence networks were also constructed to display the co-occurrence patterns of the soil fungal community. The results showed that the richness and Chao1 index both significantly increased at 50 mg kg^-1 Cu and then significantly decreased at 1600 and 3200 mg kg^-1 Cu. Soil fungal diversity was significantly and positively correlated with plant dry weight. Specific tolerant taxa under different Cu contamination gradients were illustrated by linear discriminant analysis effect size (LEfSe). Soil Cu concentration and shoot dry weight were the strongest driving factors influencing fungal composition. The relative abundance of arbuscular mycorrhizal fungi increased first and then declined along with elevating Cu concentrations via FUNGuild analysis. The interactions among fungi were enhanced under light and moderate Cu contamination but weakened under heavy Cu contamination by random matrix theory (RMT)-based molecular ecological network analysis. Penicillium, identified as a keystone taxon in Cu-contaminated soils, had the function of removing heavy metals and detoxification, which might be vital to trigger the resistance of the fungal community to Cu contamination. The results may facilitate the identification of Cu pollution indicators and the development of in situ bioremediation technology for contaminated cultivated fields.

Enhancing rhizoremediation of petroleum hydrocarbons through bioaugmentation with a plant growth-promoting bacterial consortium

The slow rate of natural attenuation of organic pollutants, together with unwanted environmental impacts of traditional remediation strategies, has necessitated the exploration of plant-microbe systems for enhanced bioremediation applications. The identification of microorganisms capable of promoting rhizoremediation through both plant growth-promoting and hydrocarbon-degrading processes is crucial to the success and adoption of plant-based remediation techniques. In this study, through successive enrichments of soil samples from a historic oil-contaminated site in Wietze, Germany, we isolated a plant growth-promoting and hydrocarbon-degrading bacterial consortium dominated by Alphaproteobacteria. In microcosm experiments involving Medicago sativa L. and the isolated bacterial consortium, we examined the ability of the consortium to enhance rhizoremediation of petroleum hydrocarbons. The inoculation of M. sativa with the consortium resulted in 66% increase in plant biomass, and achieved a 91% reduction in diesel fuel hydrocarbon concentrations in the soil within 60 days. Metagenome analysis led to the identification of genes and taxa putatively involved in these processes. The majority of the coding DNA sequences associated with plant growth promotion and hydrocarbon degradation in this study were affiliated to Acidocella aminolytica and Acidobacterium capsulatum indicating their potential for biotechnological applications in the rhizoremediation of sites contaminated by petroleum-derived organic pollutants.

Effect of soil leaching on the toxicity thresholds (ECx) of Zn in soils with different properties

Currently, the scientific basis for establishing soil environmental criteria is lacking. In order to establish reasonable soil environmental criteria values suitable for soils with different properties, this study selected soils from 16 different sites to determine the toxicity threshold of Zn based on toxicity tests of barley root elongation. In addition, leaching treatments were set up in seven soils with different properties to eliminate the influence of the accompanying anions (Cl-) on the determination of the Zn toxicity threshold. The results indicated that the toxicity thresholds of different soils vary greatly. The EC10 and EC50 ranges of barley root elongation in 16 kinds of non-leached soils were 18.5 mgkg-1 to 1618.7 mgkg-1 and 277.9 mgkg-1 to 3179.8 mgkg-1, respectively. The hormesis effect appeared in the dose response of Zn, and relative barley root elongation reached more than 150%. Leaching significantly reduced the Zn toxicity in acidic soils. The variation ranges of the leaching factor (LF) in the seven soils were LF10 = 1.1-9.3, LF50 = 1.0-3.2. The LF prediction model indicated that pH explained 81.4% of the LF variation (p < 0.01). The soil pH, cation exchange capacity (CEC), and conductivity (EC) explained 97.8% of the EC50 variation in the leached soil (p < 0.01). The results provide reference values for Zn environmental criteria.

Growth and antioxidant response in Spirodela polyrrhiza under linear alkylbenzene sulfonate, naphthalene and their joint stress

The synthetic organic surfactants linear alkylbenzene sulfonate (LAS) and polycyclic aromatic hydrocarbon naphthalene (NAP), two common organic pollutants, are frequently detected in freshwater environments. However, the combined ecotoxicological risks associated with these pollutants have not been fully elucidated. The present study investigated the effects of individual and combined treatments of LAS and NAP on the growth and physiological responses of Spirodela polyrrhiza. The results showed that LAS was the main compound toxic to S. polyrrhiza in a dose-dependent manner. The peroxidase (POD) enzyme and catalase (CAT) enzyme are the main antioxidant enzymes protecting S. polyrrhiza from LAS stress. When exposed to NAP stress alone, only slightly reversible damage was observed as the exposure time was extended (14 days). The antioxidant enzyme systems (including superoxide dismutase (SOD), CAT and POD) showed positive responses. Synergistic effects were induced with LAS-NAP mixtures (≥ 5 + 5 mg L^-1), and LAS played a major toxic role. The POD enzyme was a sensitive protective enzyme in duckweed during the joint exposure to LAS + NAP. The results indicate that LAS or NAP may cause serious damage to S. polyrrhiza and aggravate ecotoxicity in aquatic ecosystems.

Metagenome Analysis of a Hydrocarbon-Degrading Bacterial Consortium Reveals the Specific Roles of BTEX Biodegraders

Environmental contamination by petroleum hydrocarbons is of concern due to the carcinogenicity and neurotoxicity of these compounds. Successful bioremediation of organic contaminants requires bacterial populations with degradative capacity for these contaminants. Through successive enrichment of microorganisms from a petroleum-contaminated soil using diesel fuel as the sole carbon and energy source, we successfully isolated a bacterial consortium that can degrade diesel fuel hydrocarbons. Metagenome analysis revealed the specific roles of different microbial populations involved in the degradation of benzene, toluene, ethylbenzene and xylene (BTEX), and the metabolic pathways involved in these reactions. One hundred and five putative coding DNA sequences were identified as responsible for both the activation of BTEX and central metabolism (ring-cleavage) of catechol and alkylcatechols during BTEX degradation. The majority of the Coding DNA sequences (CDSs) were affiliated to Acidocella, which was also the dominant bacterial genus in the consortium. The inoculation of diesel fuel contaminated soils with the consortium resulted in approximately 70% hydrocarbon biodegradation, indicating the potential of the consortium for environmental remediation of petroleum hydrocarbons.