Transcriptional responses indicate attenuated oxidative stress in the springtail Folsomia candida exposed to mixtures of cadmium and phenanthrene

Long-term effects of oil contamination on soil quality and metabolic function

Widespread soil contamination with oil and the toxicity of petroleum hydrocarbons to soil biota make it extremely important to study microbial responses to oil stress. Soil metabolites reflect the main metabolic pathways in the soil microbial community. The examination of changes in the soil metabolic profile and metabolic function is essential for a better understanding of the nature of the pollution and restoration of the disturbed soils. The present study aimed to assess the long-term effect of oil on the ecological state of the soil, evaluate quantitative and qualitative differences in metabolite composition between soil contaminated with oil and non-contaminated soil, and reveal biologically active metabolites that are related to oil contamination and can be used for contamination assessment. A long-term field experiment was conducted to examine the effects of various oil concentrations on the biochemical properties and metabolic profile of the soil. Podzolic soil contaminated with oil demonstrated the long-term inhibition of soil biological activity and vegetation. Oil affected the metabolic activity of soil fungi increasing the production of toxic metabolites. A metabolomic approach was employed to determine soil metabolites. The metabolite profile was found to vary greatly between oil-contaminated and non-contaminated soils. Carbohydrates had the largest number of metabolites negatively affected by oil, while the content of organic acids, phenolic compounds, and terpenoids was mainly increased in oil-contaminated soil. The evaluation of the long-term impact of oil on microbial metabolism can make a valuable contribution to the assessment of soil quality and the activity of soil microorganisms being under stress from oil pollution. The results contribute to a further understanding of the role of microorganisms in the ecological functions of contaminated soil, which can be useful in the development of rehabilitation strategies for disturbed sites.

Transcriptome analysis of a springtail, Folsomia candida, reveals energy constraint and oxidative stress during petroleum hydrocarbon exposure

Petroleum hydrocarbon (PHC) contamination in soil is ubiquitous and poses harmful consequences to many organisms. The toxicity of PHC-impacted soil is difficult to predict due to variations in mixture composition and the impacts of natural weathering processes. Hence, high-throughput methods to assess PHC-impacted soils is required to expedite land management decisions. Next-generation sequencing is a robust tool that allows researchers to investigate the effects of contaminants on the transcriptome of organisms and identify molecular biomarkers. In this study, the effects of PHCs on conventional endpoints (i.e., survival and reproduction) and gene expression rates of a model springtail species, Folsomia candida were investigated. Age-synchronized F. candida were exposed to ecologically-relevant concentrations of soils spiked with fresh crude oil to calculate the reproductive EC25 and EC50 values using conventional toxicity testing. Soils spiked to these concentrations were then used to evaluate effects on the F. candida transcriptome over a 7-day exposure period. RNA-seq analysis found 98 and 132 differentially expressed genes when compared to the control for the EC25 and EC50 treatment groups, respectively. The majority of up-regulated genes were related to xenobiotic biotransformation reactions and oxidative stress response, while down-regulated genes coded for carbohydrate and peptide metabolic processes. Promotion of the pentose phosphate pathway was also found. Results suggest that the decreased reproduction rates of F. candida exposed to PHCs is due to energy constraints caused by inhibition of carbohydrate metabolic processes and allocation of remaining energy to detoxify xenobiotics. These findings provide insights into the molecular effects in F. candida following exposure to crude oil for seven days and highlight their potential to be used as a high-throughput screening test for PHC-contaminated sites. Adverse molecular effects can be measured as early as 24 h following exposure, whereas conventional toxicity tests may require a minimum of four weeks.

Heat stress delays detoxification of phenanthrene in the springtail Folsomia candida

Climate change has intensified the occurrence of heat waves, resulting in organisms being exposed to thermal and chemical stress at the same time. The effects of mild heat shock combined with sublethal concentrations of phenanthrene (PHE) on defense mechanisms in springtails Folsomia candida were investigated. The transcription of Heat Shock Protein 70 (HSP70) was significantly upregulated by heat shock but tended to reach the control levels after 42 h of recovery. The transcription of cytochrome P450 3A13 (CYP3A13) was upregulated 3-13 fold by PHE but suppressed by heat shock. The suppression by heat shock might contribute to the reduced detoxification of PHE during high-temperature exposure. In line with this, we found that the internal PHE concentration was approximately 70% higher in heat-shocked springtails than in animals kept at control temperature. In general, the transcription of genes encoding enzymes of detoxification phase Ⅱ (glutathione S-transferase 3) and phase Ⅲ (ABC transporter 1) and the activity of antioxidant defense enzymes (superoxide dismutase and catalase) were less influenced than genes encoding phase I detoxification mechanisms (CYP3A13). These results indicate that heat shock delays the detoxification of PHE in springtails.

Soil Ecotoxicology Needs Robust Biomarkers: A Meta-Analysis Approach to Test the Robustness of Gene Expression-Based Biomarkers for Measuring Chemical Exposure Effects in Soil Invertebrates

Gene expression-based biomarkers are regularly proposed as rapid, sensitive, and mechanistically informative tools to identify whether soil invertebrates experience adverse effects due to chemical exposure. However, before biomarkers could be deployed within diagnostic studies, systematic evidence of the robustness of such biomarkers to detect effects is needed. In our study, we present an approach for conducting a meta-analysis of the robustness of gene expression-based biomarkers in soil invertebrates. The approach was developed and trialed for two measurements of gene expression commonly proposed as biomarkers in soil ecotoxicology: earthworm metallothionein (MT) gene expression for metals and earthworm heat shock protein 70 (HSP70) gene expression for organic chemicals. We collected 294 unique gene expression data points from the literature and used linear mixed-effect models to assess concentration, exposure duration, and species effects on the quantified response. The meta-analysis showed that the expression of earthworm MT was strongly metal concentration dependent, stable over time and species independent. The metal concentration-dependent response was strongest for cadmium, indicating that this gene is a suitable biomarker for this metal. For copper, no clear concentration-dependent response of MT gene expression in earthworms was found, indicating MT is not a reliable biomarker for this metal. For HSP70, overall marginal up-regulation and lack of a concentration-dependent response indicated that this gene is not suitable as a biomarker for organic pollutant effects in earthworms. The present study demonstrates how meta-analysis can be used to assess the status of biomarkers. We encourage colleagues to apply this open-access approach to other biomarkers, as such quantitative assessment is a prerequisite to ensuring that the suitability and limitations of proposed biomarkers are known and stated. Environ Toxicol Chem 2022;41:2124-2138. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Synthesis of glutathione as a central aspect of PAH toxicity in liver cells: A comparison between phenanthrene, Benzo[b]Fluoranthene and their mixtures

Polycyclic Aromatic Hydrocarbons (PAH) are a class of organic pollutants normally found as mixtures with effects often hard to predict, which poses a major challenge for risk assessment. In this study, we address the effects of Phenanthrene (Phe), benzo[b]fluoranthene (B[b]F) and their mixtures (2 Phe:1 B[b]F; 1 Phe: 1 B[b]F; 1 Phe: 2 B[b]F) over glutathione (GSH) synthesis and function in HepG2 cells. We analyzed the effects on cellular viability, ROS production, glutathione (GSH) levels, protein-S-glutathionylation (PSSG), the activity of glutathione peroxidase (GPx), glutathione-S-transferases (GST) and glutathione reductase (GR). Transcript (mRNA) levels of glutathione synthesis enzymes - glutathione cysteine ligase catalytical (GCLC) and modifying (GCLM) sub-units and glutathione synthetase (GS) - and Nrf2 translocation to the nucleus were analyzed. Phe showed a higher cytotoxicity (IC₅₀ = 130 µM after 24 h) than B[b]F related to a higher ROS production (up-to 50% for Phe). In agreement, GSH levels were significantly increased (up-to 3-fold) by B[b]F and were accompanied by an increase in the levels of PSSG, which is a mechanism that protect proteins from oxidative damage. The upregulation of GSH was the consequence of Nrf2 signaling activation and increased levels of GCLC, GCLM and GS mRNA observed after exposure to B[b]F, but not during exposure to Phe. Most interestingly, all mixtures showed higher cytotoxicity than individual compounds, but intriguingly it was the 1 Phe: 1B[b]F mixture showing the highest cytotoxicity and ROS production. GSH levels were not significantly upregulated not even in the mixture enriched in B[b]F. These results point to the role of GSH as a central modulator of PAH toxicity and demonstrate the idiosyncratic behavior of PAH mixtures even when considering only two compounds in varying ratios.

Sensitivity of larval and juvenile freshwater mussels (unionidae) to ammonia, chloride, copper, potassium, and selected binary chemical mixtures

In aquatic environments, organisms such as freshwater mussels are likely exposed to complex contaminant mixtures related to industrial, agricultural, and urban activities. With growing interest in understanding the risk that chemical mixtures pose to mussels, this investigation focused on the effects of various waterborne contaminants (ammonia, chloride, copper, and potassium) and selected binary mixtures of these chemicals following a fixed-ratio design to Villosa iris glochidia and juvenile Lampsilis fasciola. In individual exposures, 48-h EC₅₀ values were determined for V. iris glochidia exposed to ammonia chloride (7.4 [95% confidence interval (CI) 6.6-8.2] mg N/L), ammonia sulfate (8.4 [7.6-9.1] mg N/L), copper sulfate (14.2 [12.9-15.4] μg Cu²⁺/L), potassium chloride (12.8 [11.9-13.7] mg K⁺/L), potassium sulfate (10.1 [8.9-11.2] mg K⁺/L), and sodium chloride (480.5 [435.5-525.5] mg Cl^-/L). The 7-d LC₅₀ values for juvenile L. fasciola were determined for potassium sulfate (45.0 [18.8-71.2] mg K⁺/L), and sodium chloride (1738.2 [1418.6-2057.8] mg Cl^-/L). In Ontario these waterborne contaminants have been reported to co-occur, with concentrations exceeding the EC₁₀ for both life stages at some locations. Data from binary mixture exposures for V. iris glochidia (chloride-ammonia, chloride-copper, and copper-ammonia) and juvenile L. fasciola (chloride-potassium) were analyzed using a regression-based, dose-response mixture analysis modeling framework. Results from the mixture analysis were used to determine if an additive model for mixture toxicity [concentration addition (CA) or independent action (IA)] best described the toxicity of each mixture and if deviation towards dose-ratio (DR) or dose-level (DL) synergism/antagonism (S/A) occurred. For all glochidia binary mixture exposures, CA was the best fit model with DL deviation reported for the chloride-copper mixture and DR deviation reported for the copper-ammonia mixture. Using the model deviation ratio (MDR), the observed toxicity in all three glochidia mixture exposures were adequately described by both CA (mean = 0.71) and IA (mean = 0.97) whereas the juvenile mixture exposure was only adequately described by CA (mean = 0.64; IA mean = 0.05).

Transgenerational and multigenerational stress gene responses to the insecticide etofenprox in Folsomia candida (Collembola)

Insecticide exposure may cause both transgenerational and multigenerational effects on populations, but the molecular mechanisms of these changes remain largely unclear. Many studies have focused on either transgenerational or multigenerational mechanisms but did neglect the comparative aspects. This study assessed whether the pyrethroid insecticide etofenprox (formulation Trebon^® 30 EC) shows transgenerational and/or multigenerational effects on the survival and reproduction of Folsomia candida (Collembola). The activation of stress-related genes was studied to detect whether etofenprox modifies the expression of reproduction-associated genes in trans- and multigenerational treatments. A laboratory study was carried out for three generations with five insecticide concentrations in LUFA 2.2 soil. In the transgenerational treatment, only the parent generation (P) was exposed, but the subsequent generations were not. In the multigenerational treatment, all three generations were exposed to the insecticide in the same manner. Multigenerational exposure resulted in reduced reproduction effects over generations, suggesting that F. candida is capable of acclimating to enhanced concentration levels of etofenprox during prolonged exposure over multiple generations. In the transgenerational treatment, the heat shock protein 70 was up-regulated and cytochrome oxidase 6N4v1 expression down-regulated in a dose-dependent manner in the F2 generation. This finding raises the possibility of the epigenetic inheritance of insecticide impacts on parents. Furthermore, CYP6N4v1 expression was oppositely regulated in the trans- and multigenerational treatments. Our results draw attention to the differences in molecular level responses of F. candida to trans- and multigenerational etofenprox exposure.

Contrasting patterns of divergence at the regulatory and sequence level in European Daphnia galeata natural populations

Understanding the genetic basis of local adaptation has long been a focus of evolutionary biology. Recently, there has been increased interest in deciphering the evolutionary role of Daphnia's plasticity and the molecular mechanisms of local adaptation. Using transcriptome data, we assessed the differences in gene expression profiles and sequences in four European Daphnia galeata populations. In total, ~33% of 32,903 transcripts were differentially expressed between populations. Among 10,280 differentially expressed transcripts, 5,209 transcripts deviated from neutral expectations and their population-specific expression pattern is likely the result of local adaptation processes. Furthermore, a SNP analysis allowed inferring population structure and distribution of genetic variation. The population divergence at the sequence level was comparatively higher than the gene expression level by several orders of magnitude consistent with strong founder effects and lack of gene flow between populations. Using sequence homology, the candidate transcripts were annotated using a comparative genomics approach. Additionally, we also performed a weighted gene co-expression analysis to identify population-specific regulatory patterns of transcripts in D. galeata. Thus, we identified candidate transcriptomic regions for local adaptation in this key species of aquatic ecosystems in the absence of any laboratory-induced stressor.

The use of gene expression to unravel the single and mixture toxicity of abamectin and difenoconazole on survival and reproduction of the springtail Folsomia candida

Pesticides risk assessments have traditionally focused on the effects on standard parameters, such as mortality, reproduction and development. However, one of the first signs of adverse effects that occur in organisms exposed to stress conditions is an alteration in their genomic expression, which is specific to the type of stress, sensitive to very low contaminant concentrations and responsive in a few hours. The aim of the present study was to evaluate the single and binary mixture toxicity of commercial products of abamectin (Kraft^® 36 EC) and difenoconazole (Score^® 250 EC) to Folsomia candida. Laboratory toxicity tests were conducted to access the effects of these pesticides on springtail survival, reproduction and gene expression. The reproduction assays gave EC₅₀ and EC₁₀ values, respectively, of 6.3 and 1.4 mg a.s./kg dry soil for abamectin; 1.0 and 0.12 mg a.s./kg dry soil for Kraft^® 36 EC; and 54 and 23 mg a.s./kg dry soil for Score^® 250 EC. Technical difenoconazole did not have any effect at the concentrations tested. No significant differences in gene expression were found between the abamectin concentrations tested (EC₁₀ and EC₅₀) and the solvent control. Exposure to Kraft^® 36 EC, however, significantly induced Cyp6 expression at the EC₅₀ level, while VgR was significantly downregulated at both the EC₁₀ and EC₅₀. Exposure to the simple pesticide mixture of Kraft^® 36 EC + Score^® 250 EC caused significant up regulation of ABC transporter, and significant down regulation of VgR relative to the controls. GABA receptor also showed significant down-regulation between the EC₁₀ and EC₅₀ mixture treatments. Results of the present study demonstrate that pesticide-induced gene expression effects precede and occur at lower concentrations than organism-level responses. Integrating "omic" endpoints in traditional bioassays may thus be a promising way forward in pesticide toxicity evaluations.

Mechanisms of phenanthrene toxicity in the soil invertebrate, Enchytraeus crypticus

Polycyclic aromatic hydrocarbons (PAHs) continue to cause environmental challenges as a result of their release into the environment by a great variety of anthropogenic activities and their accumulation in soils. Studies were conducted on the toxicological effect of the model PAH phenanthrene using the soil invertebrate model Enchytraeus crypticus at the individual, tissue, and molecular levels. Animals were exposed for 2 d and 21 d to phenanthrene concentrations corresponding to the (previously estimated) 3-wk effective concentration, 10% (EC10) and EC50 for effects on reproduction. Gene expression profiling did not reveal a typical phenanthrene-induced biotransformation signature, as it usually does in arthropods and vertebrates. Instead, after 2 d of exposure, only general metabolic processes were affected, such as translation and adenosine triphosphate synthesis-coupled electron transport. Histological sections of tissues of 2-d exposed animals showed no deviations from control. In contrast, after prolonged exposure of up to 21 d, histopathological effects were found: chloragogenous cells were highly vacuolated and hypertrophic. This was corroborated by differential expression of genes related to immune response and oxidative stress at the transcriptomic level. The data exemplify the complexity and species-specific features of PAH toxicity among soil invertebrate communities, which restricts read-across and extrapolation in the context of soil ecological risk assessment. Environ Toxicol Chem 2016;35:2713-2720. © 2016 SETAC.

Isotopic analysis of N and O in NO3- by selective bacterial reduction to N2O for groundwater pollution

We describe a method to determine the nitrogen and oxygen isotopic composition of nitrate in groundwater samples ((15)N/(14)N and (18)O/(16)O, respectively), which is based on the analysis of nitrous oxide gas (N2O) that is produced quantitatively from nitrate by denitrifying bacteria. This method which is simple, inexpensive and effective in the removal of nitrite is greatly selective for NO2(-) and was used for mixed samples containing both NO2(-) and NO3(-) with little or no measurable cross-contamination. The precision of δ(15)N and δ(18)O are 0.3 and 0.17‰ respectively, compared to that of 0.1 and 0.5‰ abroad (Brand et al. in Org Geochem 21:585-594, 1994; Begley and Scrimgeour in Anal Chem 69(8): 1530-1535, 1997; Kornexl et al. in Rapid Commun Mass Spectrom 13(16):1685-1693, 1999; Böhlke et al. in Rapid Commun Mass Spectrom 17:1835-1846, 2003; Gehre and Strauch in Rapid Commun Mass Spectrom 17(13):1497-1503, 2003; Werner in Isot Environ Health Stud 39:85-104, 2003).

Oxidative stress biomarkers and metallothionein in Folsomia candida--responses to Cu and Cd

Folsomia candida (Collembola) is a standard soil ecotoxicological species; effect assessment includes survival and reproduction as endpoints. In the present study, and for the first time, a range of oxidative stress biomarkers measurement was optimized and validated. The antioxidant capacity was measured by the activities of catalase (CAT), glutathione reductase (GR), glutathione-s-transferase (GST) and content of total glutathione (TG). The oxidative damage in the lipid membranes was estimated by lipid peroxidation (LPO) and metallothionein (MT) levels. The exposure included the essential and non-essential metals Cu and Cd, in LUFA 2.2 natural standard soil, using a series of sampling times along a 10 days period (0, 2, 4, 6 and 10 days). Exposure concentrations were selected based on their reproduction EC50 values, 60 and 1000 mg/kg soil DW, for Cd and Cu respectively. The protocols were optimized and results show that oxidative stress biomarkers can be successfully used in F. candida, this being highly relevant as complementary information to the mechanistic level. The selected sampling times gave a good indication of the markers dynamic and can be reduced/adapted in future testing. Results showed that both metals caused an increase in the MT levels after 6 days but Cd acted as a stronger oxidant agent compared to Cu, i.e. causing higher damage. In sum, Cd mobilized/activated more antioxidant enzymes, but the increased activities were not enough to prevent LPO. This study confirms that the oxidative stress caused by Cd is higher despite the use of same reproduction EC50 indicating that toxicity seems more reversible for Cu than for Cd. Among others, GST and MT would be a good selection of biomarkers for Cd effect.