Mixture effects of copper, cadmium, and zinc on mortality and behavior of Caenorhabditis elegans

The nematode Caenorhabditis elegans enhances tolerance to landfill leachate stress by increasing trehalose synthesis

The burgeoning issue of landfill leachate, exacerbated by urbanization, necessitates evaluating its biological impact, traditionally overshadowed by physical and chemical assessments. This study harnesses Caenorhabditis elegans, a model organism, to elucidate the physiological toxicity of landfill leachate subjected to different treatment processes: nanofiltration reverse osmosis tail water (NFRO), membrane bioreactor (MBR), and raw leachate (RAW). Our investigation focuses on the modulation of sugar metabolism, particularly trehalose-a disaccharide serving dual functions as an energy source and an anti-adversity molecule in invertebrates. Upon exposure, C. elegans showcased a 60-70% reduction in glucose and glycogen levels alongside a significant trehalose increase, highlighting an adaptive response to environmental stress by augmenting trehalose synthesis. Notably, trehalose-related genes in the NFRO group were up-regulated, contrasting with the MBR and RAW groups, where trehalose synthesis genes outpaced decomposition genes by 20-30 times. These findings suggest that C. elegans predominantly counters landfill leachate-induced stress through trehalose accumulation. This research not only provides insights into the differential impact of leachate treatment methods on C. elegans but also proposes a molecular framework for assessing the environmental repercussions of landfill leachate, contributing to the development of novel strategies for pollution mitigation and environmental preservation.

Caenorhabditis elegans as a suitable model to evaluate the toxicity of water from Rolante River, southern Brazil

Urbanization and agricultural activities increased environmental contaminants. Integrated analysis of water parameters and bioassays represents an essential approach to evaluating aquatic resource quality. This study aimed to assess water quality by microbiological and physicochemical parameters as well as the toxicological effects of water samples on the Ames test and Caenorhabditis elegans model. Samples were collected during (collection 1) and after (collection 2) pesticide application in the upper (S1), middle (S2), and lower (S3) sections of the Rolante River, southern Brazil. Metals were determined by GFAAS and pesticides by UPLC-MS/MS. Bioassays using the Ames test and the nematode C. elegans were performed. Levels of microbiological parameters, as well as Mn and Cu were higher than the maximum allowed limits established by legislation in collection 2 compared to collection 1. The presence of pesticide was observed in both collections; higher levels were found in collection 1. No mutagenic effect was detected. Significant inhibition of body length of C. elegans was found in collection 1 at S2 (P < 0.001) and S3 (P < 0.001) and in collection 2 at S2 (P = 0.004). Comparing the same sampling site between collections, a significant difference was found between the site of collection (F(3,6)=8.75, P = 0.01) and the time of collection (F(1,2)=28.61, P = 0.03), for the S2 and S3 samples. C. elegans model was useful for assessing surface water quality/toxicity. Results suggest that an integrated analysis for the surface water status could be beneficial for future approaches.

Evaluation the Toxicity of Heavy Metal Mixtures in Anecic Earthworms (Aporrectodea giardi)

Using earthworms as bioindicators of heavy metal contamination in soils is a relevant tool for environmental risk monitoring. This study examines the combined effects of four distinct concentrations mixtures (M1, M2, M3 and M4) containing Cd, Cr, Cu, Ni, Fe and Mn on Aporrectodea giardi earthworms after 12 and 24 days (12 D/24 D) of exposure via the monitoring of certain biomarkers of stress including total protein content, glutathione (GSH), metallothionein (MT), catalase and lipoxygenase (LOX) activities. The results show a decrease in the total protein level for the M3 mixture after 24 D, whereas it increases for all other treatments regardless of exposure time. Glutathione and metallothionine levels increased for M2 and M3 and decreased for M1 and M4 after 12 D; they increased after 24 D for all the mixtures. Regarding enzyme activities, catalase activity was decreased for all the treatments unless for M3 (P > 0.05). However, LOX increased for M1, M2 and M4 except for M3 after 12 D, when inhibition of this biomarker was observed. LOX activity was inhibited for all the mixtures at the end of the treatment. All the mixtures generated oxidative stress in Aporrectodea giardi, which is minimized by increasing MT levels to remove the metal ions and triggering the antioxidant system, composed primarily of GSH and LOX to restore cellular homeostasis. These findings suggest that the species Aporrectodea giardi could be an excellent candidate for ecotoxicological risk assessment of soils contaminated by metal mixtures and it can be used in bioremediation for its fitness which allows it to tolerate high concentrations of metal mixtures.

Recent Advances in Drug Discovery Toxicology

Major advances in scientific discovery and insights that stem from the development and use of new techniques and models can bring remarkable progress to conventional toxicology. Although animal testing is still considered as the "gold standard" in traditional toxicity testing, there is a necessity for shift from animal testing to alternative methods regarding the drug safety testing owing to the emerging state-of-art techniques and the proposal of 3Rs (replace, reduce, and refine) towards animal welfare. This review describes some recent research methods in drug discovery toxicology, including in vitro cell and organ-on-a-chip, imaging systems, model organisms (C. elegans, Danio rerio, and Drosophila melanogaster), and toxicogenomics in modern toxicology testing.

Exposure to epoxy-modified nanoplastics in the range of μg/L causes dysregulated intestinal permeability, reproductive capacity, and mitochondrial homeostasis by affecting antioxidant system in Caenorhabditis elegans

Although surface chemically modified nanopolystyrene (PS) has been reported to have potential toxicity toward organisms, the impact of epoxy modification on the toxicity of PS remains largely unknown. In this study, we first investigated the prolonged exposure effects of epoxy-modified PS (PS-C2H3O) in the range of μg/L on Caenorhabditis elegans (C. elegans) including general toxicity, target organ toxicity, and organelle toxicity. Our data revealed that C. elegans exposed to PS-C2H3O led to the alterations in increased lethality (≥ 1000 μg/L), shortened body length (≥ 100 μg/L), and decreased locomotion capacity (≥ 1 μg/L). In addition, toxicity analysis on target organs and organelles indicated that exposure to PS-C2H3O enhanced intestinal permeability (≥ 100 μg/L) by inhibiting the transcriptional levels of acs-22 (encoding fatty acid transport protein) (≥ 100 μg/L) and hmp-2 (encoding α-catenin) (≥ 1000 μg/L), reduced reproductive capacity (≥ 10 μg/L), and dysregulated mitochondrial homeostasis (≥ 1 μg/L). Moreover, the activation of antioxidant enzyme system could help nematodes against the toxicity caused by PS-C2H3O exposure (≥ 10 μg/L). Furthermore, we also compared the toxicity of PS-C2H3O with other chemically modified derivatives of PS, and the toxicity order was PS-NH2 > PS-SOOOH > PS-C2H3O > PS-COOH > PS > PS-PEG. Our study highlights the potential environmental impact of PS and its derivatives on organisms and suggests that the toxicity of nanoplastics may be charge-dependent.

Heavy metal pollution triggers a shift from bacteria-based to fungi-based soil micro-food web: Evidence from an abandoned mining-smelting area

Heavy metals pose significant threats to soil biota, ultimately disrupting soil micro-food web. However, no studies have yet elucidated the impact of heavy metals on soil micro-food web. In this study, we explored the response of bacteria, fungi, nematodes, and soil micro-food web along a gradient of heavy metals in an abandoned smelting-mining area. We found that bacteria responded strongly to heavy metals, whereas fungi showed greater resistance and tolerance. Nematodes responses were less apparent. With the increasing levels of heavy metal pollution, the importance of heavy metal-tolerant organisms in micro-food webs increased significantly. For instance, the keystone bacteria in soil micro-food web shifted from copiotrophic to oligotrophic types, while the keystone nematodes shifted from to bacterial-feeding (e.g., Eucephalobus) to fungal-feeding species (e.g., Ditylenchus). Additionally, elevated heavy metal concentrations increased the proportion of fungi (e.g., Mortierellomycota), intensifying their interactions with bacteria and nematodes and causing a shift from bacteria-based to fungi-based soil micro-food web. Furthermore, heavy metal contamination induced a more complex and stable soil micro-food web. Overall, we highlight the changes in soil micro-food web as a mechanism for coping with heavy metal stress. Our study provides valuable insights into how heavy metal pollution can cause shifts in soil micro-food webs and has critical implications for enhancing our understanding of the ecological consequences of environmental pollution at the ecosystem level.

An automatic recognition method of nematode survival rate based on bright field and dark field experimental images

BACKGROUND

The survival rate of experimental animals is a very important index in chemical toxicity evaluation experiments. The calculation of nematode survival rate is used in many experiments.

OBJECTIVE

Traditional survival rate quantification methods require manual counting. This is a time-consuming and laborious work when using 384-well plate for high-throughput chemical toxicity assessment experiments. At present, there is a great need for an automatic method to identify the survival rate of nematodes in the experiment of chemical toxicity evaluation.

METHODS

We designed an automatic nematode survival rate recognition method by combining the bright field experimental image of nematodes and the dark field image of nematodes which is captured after adding Propidium Iodide dye, and used it to calculate the nematode survival rate in different chemical environments. Experiment results show that the survival rate obtained by our automatic counting method is very similar to the survival rate obtained by manual counting.

RESULTS

Through several different chemical experiments, we can see that chemicals with different toxicity have different effects on the survival rate of nematodes. And the survival rate of nematodes under different chemical concentrations has an obvious gradient trend from high concentration to low concentration. In addition, our method can quantify the motility of nematodes. There are also significant differences in the motility of nematodes cultured in different chemical environments. Moreover, the nematode motility under different chemical concentrations showed an obvious gradient change trend from high concentration to low concentration.

CONCLUSION

Our study provides an accurate and efficient nematode survival rate recognition method for chemical toxicology research.

Exposure to 6-PPD Quinone at Environmentally Relevant Concentrations Causes Abnormal Locomotion Behaviors and Neurodegeneration in Caenorhabditis elegans

6-PPD quinone (6-PPDQ) can be transformed from 6-PPD through ozonation. Nevertheless, the potential neurotoxicity of 6-PPDQ after long-term exposure and the underlying mechanism are largely unclear. In Caenorhabditis elegans, we here observed that 0.1-10 μg/L of 6-PPDQ caused several forms of abnormal locomotion behaviors. Meanwhile, the neurodegeneration of D-type motor neurons was observed in 10 μg/L of 6-PPDQ-exposed nematodes. The observed neurodegeneration was associated with the activation of the Ca²⁺ channel DEG-3-mediated signaling cascade. In this signaling cascade, expressions of deg-3, unc-68, itr-1, crt-1, clp-1, and tra-3 were increased by 10 μg/L of 6-PPDQ. Moreover, among genes encoding neuronal signals required for the control of stress response, expressions of jnk-1 and dbl-1 were decreased by 0.1-10 μg/L of 6-PPDQ, and expressions of daf-7 and glb-10 were decreased by 10 μg/L of 6-PPDQ. RNAi of jnk-1, dbl-1, daf-7, and glb-10 resulted in the susceptibility to 6-PPDQ toxicity in decreasing locomotory ability and in inducing neurodegeneration, suggesting that JNK-1, DBL-1, DAF-7, and GLB-10 were also required for the induction of 6-PPDQ neurotoxicity. Molecular docking analysis further demonstrated the binding potential of 6-PPDQ to DEG-3, JNK-1, DBL-1, DAF-7, and GLB-10. Together, our data suggested the exposure risk of 6-PPDQ at environmentally relevant concentrations in causing neurotoxicity in organisms.

Recombinant human metallothionein-III alleviates oxidative damage induced by copper and cadmium in Caenorhabditis elegans

Recombinant human metallothionein III (rh-MT-III) is a genetically engineered product produced by Escherichia coli fermentation technology. Its molecules contain abundant reducing sulfhydryl groups, which possess the ability to bind heavy metal ions. The present study was to evaluate the binding effects of rh-MT-III against copper and cadmium in vitro and to investigate the antioxidant activity of rh-MT-III using Caenorhabditis elegans in vivo. For in vitro experiments, the binding rates of copper and cadmium were 91.4% and 97.3% for rh-MT-III at a dosage of 200 μg/mL at 10 h, respectively. For in vivo assays, the oxidative stress induced by copper (CuSO₄ , 10 μg/mL) and cadmium (CdCl₂ , 10 μg/mL) was significantly reduced after 72 h of exposure to different doses of rh-MT-III (5-500 μg/mL), indicated by restoring locomotion behavior and growth, and reducing malondialdehyde and reactive oxygen species levels in C. elegans. Moreover, rh-MT-III decreased the deposition of lipofuscin and fat content, which could delay the progression of aging. In addition, rh-MT-III (500 μg/mL) promoted the up-regulation of Mtl-1 and Mtl-2 gene expression in C. elegans, which could enhance the resistance to oxidative stress by increasing the enzymatic activity of antioxidant defense system and scavenging free radicals. The results indicated that supplemental rh-MT-III could effectively protect C. elegans from heavy metal stress, providing an experimental basis for the future application and development of rh-MT-III.

Hydroalcoholic extract of Haematoxylum brasiletto protects Caenorhabditis elegans from cadmium-induced toxicity

Background

H. brasiletto is used in popular culture due to its therapeutic properties, including antioxidant, anti-inflammatory and antiproliferative properties, although little is known about its role as a protector against metal toxicity. This study aimed to investigate the chemical composition and efficacy of the hydroalcoholic extract from H. brasiletto (HAE-Hbrasiletto) collected in northern Colombia to defend against cadmium (Cd)-induced toxicity.

Methods

Phytochemical characterization was performed using HPLC-ESI-QTOF. Caenorhabditis elegans was employed to assess the shielding effect of HAE-Hbrasiletto against Cd toxicity in vivo, and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was utilized to measure radical scavenging activity.

Results

The main secondary metabolites identified by HPLC-ESI-QTOF in the extracts were hematoxylins (brazilein and hematein) and protosappanins (protosappanin A, B and C, 10-O-methylprotosappanin B, and protosappanin A dimethyl acetal). The HAE-Hbrasiletto elicited low lethality in N2 worms and significantly reduced the Cd-induced death of the nematodes. It also improved Cd-induced motility inhibition, as well as body length and reproduction reduction provoked by the heavy metal. The extract displayed a good capacity to halt Cd-induced DAF-16 translocation. As this last process was associated with lethality (r = 0.962, p < 0.01), the antioxidant properties of the extract may contribute to ameliorating tissue damage induced by oxidative stress from Cd exposure.

Conclusion

HAE-Hbrasiletto has remarkable properties to protect against Cd-induced toxicity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-022-03654-6.

Most secondary metabolites tentatively identified in H. brasiletto are homoisoflavones.

Hidroalcoholic extract of H. brasiletto protects C. elegans from Cd toxicity

The extract diminished Cd-induced damage to reproduction, growth, and locomotion.

Cd-induced oxidative stress and translocation of DAF-16 are blocked by the extract.

A Matter of Metals: Copper but Not Cadmium Affects the Microbial Alpha-Diversity of Soils and Sediments - a Meta-analysis

Heavy metal (HM) accumulation in soil affects plants and soil fauna, yet the effect on microbial alpha-diversity remains unclear, mainly due to the absence of dedicated research synthesis (e.g. meta-analysis). Here, we report the first meta-analysis of the response of soil microbial alpha-diversity to the experimental addition of cadmium (Cd) and copper (Cu). We considered studies conducted between 2013 and 2022 using DNA metabarcoding of bacterial and fungal communities to overcome limitations of other cultivation- and electrophoresis-based techniques. Fungi were discarded due to the limited study number (i.e. 6 studies). Bacterial studies resulted in 66 independent experiments reported in 32 primary papers from four continents. We found a negative dose-dependent response for Cu but not for Cd for bacterial alpha-diversity in the environments, only for Cu additions exceeding 29.6 mg kg^-1 (first loss of - 0.06% at 30 mg kg^-1). The maximal loss of bacterial alpha-diversity registered was 13.89% at 3837 mg kg^-1. Our results first highlight that bacterial communities behave differently to soil pollution depending on the metal. Secondly, our study suggests that even extreme doses of Cu do not cause a dramatic loss in alpha-diversity, highlighting how the behaviour of bacterial communities diverges from soil macro-organisms.

Introduction of Flavor Chemical Eugenol Attenuating the Synergistic Toxicological Interactions of Flavor Mixtures

The flavor chemicals benzyl alcohol (BEA), phenylethanol (PHA), and cinnamaldehyde (CID) and their binary mixtures have high toxicity sensitivity to the lethal endpoint of Caenorhabditis elegans. Some binary flavor mixtures even have synergistic toxicological interactions. Eugenol (EUG) is closely related to human life and has many special nonlethal effects on organisms. The effect of its introduction on the combined toxicities of flavor mixtures is worth studying. We introduced EUG into three binary (BEA-PHA, BEA-CID, and PHA-CID) and one ternary (BEA-PHA-CID) flavor mixture systems. Five representative mixture rays were selected from each of the four mixture systems using the uniform design ray (UD-Ray) method. The lethal toxicity of each mixture ray to C. elegans was measured at three different exposure volumes (100, 200, and 400 μL), and a dose-effect model was established. The new parameter iSPAN was used to quantitatively characterize the toxicity sensitivity of each chemical and mixture ray. The toxicological interaction of each mixture was evaluated by the toxicological interaction heatmap based on the combination index (CI). It can be seen that all flavor chemicals and their ternary and quaternary mixture rays have high iSPANs, and the highest value is 16.160 (BEA-PHA-CID-EUG-R1 at 400 μL). According to the heatmap and CI, the introduction of EUG attenuates the synergistic toxicological interactions of flavor mixtures, leading to the transformation ofsynergistic interactions in flavor mixtures into additive action and even antagonistic interaction, and the CI value of the antagonistic interaction is up to 1.8494 (BEA-CID-EUG-R4 at 400 μL).

Interactive toxicity of copper and cadmium in regenerating and adult planarians

In a polluted environment, metals are present as complex mixtures. As a result, organisms are exposed to different metals at the same time, which affects both metal-specific as well as overall toxicity. Detailed information about the molecular mechanisms underlying the adverse effects of combined exposures remains limited in terms of different life stages. In this study, the freshwater planarian Schmidtea mediterranea was used to investigate developmental and physiological responses associated with a combined exposure to Cu and Cd. In addition, the cellular and molecular mechanisms underlying the provoked adverse effects were studied in different exposure scenarios. Mixed exposure resulted in a decline in survival, diverse non-lethal morphological changes, neuroregenerative impairments, altered behaviour and a limited repair capacity. Underlying to these effects, the cellular redox state was altered in all exposure conditions. In adult animals, this led to DNA damage and corresponding transcriptional changes in cell cycle and DNA repair genes. In regenerating animals, changes in hydrogen peroxide and glutathione contents led to regenerative defects. Overall, our results demonstrate that (1) developing organisms are more susceptible to metal exposures, and (2) the toxicity of an individual metal increases significantly in a mixed exposure scenario. These aspects have to be included in current risk assessment strategies.

Copper and Chromium toxicity is mediated by oxidative stress in Caenorhabditis elegans: The use of nanoparticles as an immobilization strategy

Environmental contamination by heavy metals (HMs) has impelled searching for stabilization strategies, where the use of zero-valent iron nanoparticles (nZVI) is considered a promising option. We have evaluated the combined effect of Cu(II)-Cr(VI) on two Caenorhabditis elegans strains (N2 and RB1072 sod-2 mutant) in aqueous solutions and in a standard soil, prior and after treatment with nZVI (5% w/w). The results showed that HMs aqueous solutions had an intense toxic effect on both strains. Production of reactive oxygen species and enhanced expression of the heat shock protein Hsp-16.2 was observed, indicating increased HM-mediated oxidative stress. Toxic effects of HM-polluted soil on worms were higher for sod-2 mutant than for N2 strain. However, nZVI treatment significantly diminished all these effects. Our findings highlighted C. elegans as a sensitive indicator for HMs pollution and its usefulness to assess the efficiency of the nanoremediation strategy to decrease the toxicity of Cu(II)-Cr(VI) polluted environments.

Enhanced Uptake of Arsenic Induces Increased Toxicity with Cadmium at Non-Toxic Concentrations on Caenorhabditis elegans

Cadmium (Cd) and arsenic (As) are widely distributed pollutants that co-exist in the environment; however, their joint toxicity on living organisms is still largely unknown. In this study, we explored the joint toxicity of concurrent exposure to Cd and different As species at low concentrations on Caenorhabditis elegans (C. elegans) in comparison to single exposures. Endpoints such as germ cell apoptosis, the number of oocytes, brood size, and the life span were employed to evaluate the combined effects of Cd and As on exposed C. elegans from L3 or L4 stages. Our results showed that concurrent exposure to non-toxic concentrations of Cd and As caused the synergy of reproductive and developmental toxicity. The presence of Cd promoted the accumulation of As in both germline and intestine detected by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Although a conversion of As(III) to As(V) was detected as dependent on pH according to the microenvironment of the intestine in the worm, there was no significant difference of toxicity in C. elegans concurrently exposed to Cd and different As species. Using loss-of-function mutant strains, As was deemed responsible for the enhanced joint toxicity, and in which gcs-1 played a key protective role. These data help to better evaluate the comprehensive adverse effects of concurrent exposure of heavy metals at low concentrations on living organisms in the environment.

Study on the Combined Toxicities and Quantitative Characterization of Toxicity Sensitivities of Three Flavor Chemicals and Their Mixtures to Caenorhabditis elegans

It was shown that flavor chemicals with high toxicity sensitivities mean that small changes in their effective concentrations can lead to significant changes in toxicity. Flavors are widely used in personal care products. However, our study demonstrated that some flavor chemicals and their mixture rays have high toxicity sensitivities to Caenorhabditis elegans (C. elegans), which may have an impact on human health. In this paper, three flavor chemicals (benzyl alcohol, phenethyl alcohol, and cinnamaldehyde) were used as components of the mixture, and three binary mixture systems were constructed, respectively. Five mixture rays were designed for each mixture system by a direct equipartition ray design method. The lethal toxicities of the three flavor chemicals and mixture rays to C. elegans at three exposure volumes were determined. A new concept (inverse of the negative logarithmic concentration span (iSPAN)) was introduced to quantitatively evaluate the toxicity sensitivity of chemicals or mixture rays, and the combination index (CI) was employed to identify the toxicological interactions in the mixtures. It was shown that the three flavor chemicals as well as the binary mixture rays have a significant concentration-response relationship on the lethality of C. elegans. The iSPAN values of the three flavor chemicals and their mixture rays were larger than 3.000, showing very strong toxicity sensitivity to C. elegans. In mixture systems, the toxicity sensitivities of mixture rays with different mixture ratios were also different at different exposure volumes. In addition, it can be seen from the CI heat map that the toxicological interaction not only shows the mixture ratio dependence but also changes with the different exposure volumes, which implies that the mixtures consisting of flavor chemicals with high toxicity sensitivity have complex toxicological interactions. Therefore, in environmental risk assessment, special attention should be paid to chemicals with high toxicity sensitivities.

Cadmium hijacks the high zinc response by binding and activating the HIZR-1 nuclear receptor

Cadmium is an environmental pollutant and significant health hazard that is similar to the physiological metal zinc. In Caenorhabditis elegans, high zinc homeostasis is regulated by the high zinc activated nuclear receptor (HIZR-1) transcription factor. To define relationships between the responses to high zinc and cadmium, we analyzed transcription. Many genes were activated by both high zinc and cadmium, and hizr-1 was necessary for activation of a subset of these genes; in addition, many genes activated by cadmium did not require hizr-1, indicating there are at least two mechanisms of cadmium-regulated transcription. Cadmium directly bound HIZR-1, promoted nuclear accumulation of HIZR-1 in intestinal cells, and activated HIZR-1-mediated transcription via the high zinc activation (HZA) enhancer. Thus, cadmium binding promotes HIZR-1 activity, indicating that cadmium acts as a zinc mimetic to hijack the high zinc response. To elucidate the relationships between high zinc and cadmium detoxification, we analyzed genes that function in three pathways: the pcs-1/phytochelatin pathway strongly promoted cadmium resistance but not high zinc resistance, the hizr-1/HZA pathway strongly promoted high zinc resistance but not cadmium resistance, and the mek-1/sek-1/kinase signaling pathway promoted resistance to high zinc and cadmium. These studies identify resistance pathways that are specific for high zinc and cadmium, as well as a shared pathway.

Defining drinking water metal contaminant mixture risk by coupling zebrafish behavioral analysis with citizen science

Contaminated drinking water is an important public health consideration in New England where well water is often found to contain arsenic and other metals such as cadmium, lead, and uranium. Chronic or high level exposure to these metals have been associated with multiple acute and chronic diseases, including cancers and impaired neurological development. While individual metal levels are often regulated, adverse health effects of metal mixtures, especially at concentrations considered safe for human consumption remain unclear. Here, we utilized a multivariate analysis that examined behavioral outcomes in the zebrafish model as a function of multiple metal chemical constituents of 92 drinking well water samples, collected in Maine and New Hampshire. To collect these samples, a citizen science approach was used, that engaged local teachers, students, and scientific partners. Our analysis of 4016 metal-mixture combinations shows that changes in zebrafish behavior are highly mixture dependent, and indicate that certain combinations of metals, especially those containing arsenic, cadmium, lead, and uranium, even at levels considered safe in drinking water, are significant drivers of behavioral toxicity. Our data emphasize the need to consider low-level chemical mixture effects and provide a framework for a more in-depth analysis of drinking water samples. We also provide evidence for the efficacy of utilizing citizen science in research, as the broader impact of this work is to empower local communities to advocate for improving their own water quality.

Superoxide dismutase 1 (SOD1) and cadmium: A three models approach to the comprehension of its neurotoxic effects

Cadmium (Cd) is a widespread toxic environmental contaminant, released by anthropogenic activities. It interferes with essential metal ions homeostasis and affects protein structures and functions by substituting zinc, copper and iron. In this study, the effect of cadmium on SOD1, a CuZn metalloenzyme catalyzing superoxide conversion into hydrogen peroxide, has been investigated in three different biological models. We first evaluated the effects of cadmium combined with copper and/or zinc on the recombinant GST-SOD1, expressed in E. coli BL21. The enzyme activity and expression were investigated in the presence of fixed copper and/or zinc doses with different cadmium concentrations, in the cellular medium. Cadmium caused a dose-dependent reduction in SOD1 activity, while the expression remains constant. Similar results were obtained in the cellular model represented by the human SH-SY5Y neuronal cell line. After cadmium treatment for 24 and 48 h, SOD1 enzymatic activity decreased in a dose- and time-dependent way, while the protein expression remained constant. Finally, a 16 h cadmium treatment caused a 25 % reduction of CuZn-SOD activity without affecting the protein expression in the Caenorhabditis elegans model. Taken together our results show an inhibitory effect of cadmium on SOD1 enzymatic activity, without affecting the protein expression, in all the biological models used, suggesting that cadmium can displace zinc from the enzyme catalytic site.

Toxicity of binary mixtures of Cu, Cr and As to the earthworm Eisenia andrei

Chromated copper arsenate (CCA) mixtures were used in the past for wood preservation, leading to large scale soil contamination. This study aimed at contributing to the risk assessment of CCA-contaminated soils by assessing the toxicity of binary mixtures of copper, chromium and arsenic to the earthworm Eisenia andrei in OECD artificial soil. Mixture effects were related to reference models of Concentration Addition (CA) and Independent Action (IA) using the MIXTOX model, with effects being related to total and available (H₂O and 0.01 M CaCl₂ extractable) concentrations in the soil. Since only in mixtures with arsenic dose-related mortality occurred (LC₅₀ 92.5 mg/kg dry soil), it was not possible to analyze the mixture effects on earthworm survival with the MIXTOX model. EC₅₀s for effects of Cu, Cr and As on earthworm reproduction, based on total soil concentrations, were 154, 449 and 9.1 mg/kg dry soil, respectively. Effects of mixtures were mainly antagonistic when related to the CA model but additive related to the IA model. This was the case when mixture effects were based on total and H₂O-extractable concentrations; when based on CaCl₂-extractable concentrations effects mainly were additive related to the CA model except for the Cr-As mixture which acted antagonistically. These results suggest that the CCA components do interact leading to a reduced toxicity when present in a mixture.

Intergenerational toxicity of nonylphenol ethoxylate (NP-9) in Caenorhabditis elegans

The ethoxylated isomers of nonylphenol (NPEs, NP-9) are one of the main active ingredients present in nonionic surfactants employed as herbicides, cosmetics, paints, plastics, disinfectants and detergents. These chemicals and their metabolites are commonly found in environmental matrices. The aim of this work was to evaluate the intergenerational toxicity of NP-9 in Caenorhabditis elegans. The lethality, length, width, locomotion and lifespan were investigated in the larval stage L4 of the wild strain N2. Transgenic green fluorescent protein (GFP) strains were employed to estimate changes in relative gene expression. RT-qPCR was utilized to measure mRNA expression for neurotoxicity-related genes (unc-30, unc-25, dop-3, dat-1, mgl-1, and eat-4). Data were obtained from parent worms (P0) and the first generation (F1). Lethality of the nematode was concentration-dependent, with 48 h-LC₅₀ values of 3215 and 1983 μM in P0 and F1, respectively. Non-lethal concentrations of NP-9 reduced locomotion. Lifespan was also decreased by the xenobiotic, but the negative effect was greater in P0 than in F1. Non-monotonic concentration-response curves were observed for body length and width in both generations. The gene expression profile in P0 was different from that registered in F1, although the expression of sod-4, hsp-70, gpx-6 and mtl-2 increased with the surfactant concentration in both generations. None of the tested genes followed a classical concentration-neurotoxicity relationship. In P0, dopamine presented an inverted-U curve, while GABA and glutamate displayed a bimodal type. However, in F1, inverted U-shaped curves were revealed for these genes. In summary, NP-9 induced intergenerational responses in C. elegans through mechanisms involving ROS, and alterations of the GABA, glutamate, and dopamine pathways.

Sensitivity to Copper and Development of Culturing and Toxicity Test Procedures for the Antarctic Terrestrial Nematode Plectus murrayi

Environmental quality guideline values and remediation targets, specific to Antarctic ecosystems, are required for the risk assessment and remediation of contaminated sites in Antarctica. Ecotoxicological testing with Antarctic soil organisms is fundamental in determining reliable contaminant effect threshold concentrations. The present study describes the development of optimal culturing techniques and aqueous toxicity test procedures for an endemic Antarctic soil nematode, Plectus murrayi, which lives within interstitial waters between soil particles. Toxicity tests were of extended duration to account for the species' physiology and life-history characteristics. Plectus murrayi was sensitive to aqueous copper with a 50% effective concentration for egg-hatching success of 139 µg/L. Hatched juveniles that were first exposed to copper as eggs appeared to be less sensitive than those first exposed at the hatched J2 stage, indicating a potential protective effect of the egg. Sensitivity of juveniles to copper increased with exposure duration, with 50% lethal concentrations of 478 and 117 µg/L at 21 and 28 d, respectively. The present study describes new methods for the application of an environmentally relevant test species to the risk assessment of contaminants in Antarctic soil and provides the first estimates of sensitivity to a toxicant for an Antarctic terrestrial microinvertebrate. Environ Toxicol Chem 2020;39:482-491. © 2019 SETAC.

Airborne toluene exposure causes germline apoptosis and neuronal damage that promotes neurobehavioural changes in Caenorhabditis elegans

Toluene is a highly volatile organic solvent present in gasoline. Exposure mainly occurs by absorption via the pulmonary tract and easily reaches the central nervous system, which causes toxic effects. Toluene toxicity has been described but not well established. The present work aimed to evaluate the effects of airborne exposure to toluene, the in vivo model Caenorhabditis elegans was assessed to determine whether nematode could be used to evaluate the effects of exposure to toluene and the possible mechanisms of toxicity of the solvent. Worms at the first or fourth larval stages were exposed to toluene for 48 or 24 h, respectively, in a laboratory-developed vapor chamber at concentrations of 450, 850, 1250 and 1800 ppm. We observed increases in worm mortality and significant developmental delays that occurred in a concentration-dependent manner. An increased incidence of apoptotic events in treated germline cells was shown, which was consistent with observed reductions in reproductive capacity. In addition, toluene promoted significant behavioural changes affecting swimming movements and radial locomotion, which were associated with changes in the fluorescence intensity and morphology of GABAergic and cholinergic neurons. We conclude that toluene exposure was toxic to C. elegans, with effects produced by the induction of apoptosis and neuronal damage.

Novel Polymeric Nanocarriers Reduced Zinc and Doxycycline Toxicity in the Nematode Caenorhabditis elegans

The objective was to evaluate the toxicity of zinc- and doxycycline-loaded polymeric nanoparticles (NPs) using Caenorhabditis elegans as a model organism. These NPs are composed of ethylene glycol dimethacrylate, 2-hydroxyethyl methacrylate and methacrylic acid. NPs were loaded with doxycycline (D-NPs) and zinc (Zn-NPs) by chemical adsorption, and loading efficacy was demonstrated. Worm death rate in a concentration-response curve basis was calculated for lethality. Metabolism was evaluated through pharyngeal pumping assay. Body length measurements, brood size and egg lays were used to gauge growth, reproduction and fertility respectively. Intracellular hydrogen peroxide levels were determined to assess the reactive oxygen species production. One-way ANOVA and Bonferroni were used for comparisons (p < 0.05). Tested NPs at the highest dosage did not affect lethality or worm metabolism, expressed in terms of death rate and pharyngeal pumping per minute, respectively. Zn-NPs slightly increased worm growth. The concentration of the intracellular hydrogen peroxide levels was the lowest in the D-NPs group. The distinct NPs and concentrations employed were shown to be non-toxic for in situ administration of zinc and doxycycline, reducing the harmful effects of these compounds.

High-throughput assessment of toxic effects of metal mixtures of cadmium(Cd), lead(Pb), and manganese(Mn) in nematode Caenorhabditis elegans

Heavy metals, a class of persistent environmental toxicants, are harmful to human health. Cd and Pb are two of the most common toxic heavy metals that have been linked with cancers and malfunction of the nervous system. Notably, contamination of Mn usually coexisted with Cd and Pb in environmental and occupational settings. Studies regularly examined the toxic effects on individual metals; however, potential health and toxic effects of mixtures containing two or more heavy metals are unknown. Here, we investigated toxic effects of Cd, Pb, Mn, and their binary and ternary mixtures in the nematode Caenorhabdities elegans. The toxic outcomes, including effects on growth, reproduction, and feeding, were measured via high-throughput platform analysis. The transgenic strain BY250 with GFP in dopaminergic neurons was used to explore the neurodegenerative effects induced by single metals or their mixtures. The combination index(CI) for mixtures effect was calculated using isobolograms methods. Following the exposure, we found significant toxic effects in C. elegans. For single metals, the toxicity order for growth, reproduction, and feeding were Pb > Cd > Mn. For mixtures, the mixture of Cd + Mn induced a less than addictive effect in C. elegans, whereas the mixtures of Cd + Pb, Pb + Mn, and Cd + Pb + Mn induced greater-than-additive effects. Both single metals and their mixtures induced abnormality in dopaminergic neurons. These results showed combinative toxic and neurodegenerative effects of heavy metal mixtures, and future studies will focus on characterization of concentration-response patterns and identification of potential molecular mechanisms in C. elegans model.

The effect of metal mixture composition on toxicity to C. elegans at individual and population levels

The toxicity of zinc (Zn), copper (Cu), and cadmium (Cd) to the nematode Caenorhabditis elegans was characterised under single metal and mixture scenarios at different organisational levels. The effects on population size and body length were investigated at two concentrations corresponding to the 24 h LC5 and LC20 levels. Metal toxicity was dependent on metal concentration, exposure time and mixture composition. Populations exposed to LC20 levels of Cd, ZnCu, CuCd and ZnCuCd plummeted, while for all LC5 concentrations, population size continued to increase, albeit that single metals were less harmful than mixtures. Combinations of the LC20 concentration of Cd with a range of Zn concentrations showed concentration dependent mitigating effects on population size and antagonistic effects on mortality. By combining effects at different organisational levels, more insight into metal toxicity was obtained. Metal effects were more evident on population size than on body length or mortality, suggesting that population size could be considered as a sensitive endpoint. Furthermore, our observations of ZnCd mixture effects at the individual and population levels are consistent with literature data on the dose-dependent expression of the cdf-2 gene, which is involved in mediation of Zn and Cd toxicity.

Wood ash decreases cadmium toxicity to the soil nematode Caenorhabditis elegans

Wood ash is a beneficial fertilizer and liming agent in nutrient depleted soils, but it also contains considerable amounts of cadmium (Cd), which can be toxic to organisms in the environment. Therefore, risk assessments regarding utilization of wood ash is required. Here, we studied how wood ash (applied in doses equivalent to 0, 3 and 6 t ha^-1) and Cd (applied in doses of 0, 10, 150, 300, 600, 1200 and 2000 mg kg^-1) affected growth of the soil nematode Caenorhabditis elegans. The treatments were combined in a full factorial design. Wood ash alone greatly stimulated both soil respiration and growth of C. elegans, whereas Cd alone had a toxic effect. However, unrealistically high Cd levels were needed to severely affect growth of C. elegans and soil respiration, especially soil respiration was very resilient to Cd amendment. Ash addition decreased Cd toxicity to C. elegans, with an EC₅₀ value of 390 mg Cd kg^-1 in the 3 t ash ha^-1 treatment, and an increase of EC₅₀ to 1894 mg Cd kg^-1 in the 6 t ash ha^-1 treatment. This is probably because ash increases the Cd sorption capacity of the soil, and thereby decreases the bio-availability of Cd. The results suggest that there is no acute toxic effect of Cd to nematodes associated with wood ash recycling; in fact, our results suggest that ash actually decrease Cd toxicity.

Caenorhabditis elegans as a tool for environmental risk assessment: emerging and promising applications for a "nobelized worm"

Caenorhabditis elegans has been an invaluable model organism in research fields such as developmental biology and neurobiology. Neurotoxicity is one of the subfields greatly profiting from the C. elegans model within biomedical context, while the corresponding potential of the organism applied to environmental studies is relevant but has been largely underexplored. Within the biomedical scope, the implication of metals and organic chemicals with pesticide activity (hereinafter designated as pesticides) in the etiology of several neurodegenerative diseases has been extensively investigated using this nematode as a primary model organism. Additionally, as a well-known experimental model bearing high sensitivity to different contaminants and representing important functional levels in soil and aquatic ecosystems, C. elegans has high potential to be extensively integrated within Environmental Risk Assessment (ERA) routines. In spite of the recognition of some regulatory agencies, this actual step has yet to be made. The purpose of this review is to discuss the major advantages supporting the inclusion of C. elegans in lower tiers of ERA. Special emphasis was given to its sensitivity to metals and pesticides, which is similar to that of other model organisms commonly used in ERA (e.g. Daphnia magna and Eisenia sp.), and to the large array of endpoints that can be tested with the species, both concerning the aquatic and the soil compartments. The inclusion of C. elegans testing may hence represent a relevant advance in ERA, providing ecologically relevant insights toward improvement of the regulatory capacity for establishing appropriate environmental protection benchmarks.

Combined exposure to methylmercury and manganese during L1 larval stage causes motor dysfunction, cholinergic and monoaminergic up-regulation and oxidative stress in L4 Caenorhabditis elegans

Humans are exposed simultaneously to a variety of neurotoxic agents, including manganese (Mn) and methylmercury (MeHg). Therefore, the study of combined exposures to toxicants is timely. This work aimed to study changes in cholinergic system focusing on acetylcholinesterase (ace-2), monoaminergic system focusing on vesicular monoamine transporter (VMAT, cat-1) expression, to address changes in antioxidant enzymatic systems, namely, the expression of superoxide dismutase (sod-3 and sod-4) and catalase (ctl-3), as well as worm reproduction and locomotion. C. elegans in the L1 larval stage were exposed to Mn, MeHg or both. All analyses were done 24 h after the end of exposure, except for behavior and reproduction tests that were assessed in L4 larval stage worms. The values obtained for lethal dose 50% (LD50) were 17.78 mM for Mn and 30.63 μM for MeHg. It was observed that body bends, pharyngeal pumping and brood size decreased in worms exposed to metals when undergoing combined exposures. Relative mRNA content of ace-2, cat-1, sod-3, sod-4 and ctl-3 was increased at the highest concentration of the interaction (50 mM Mn + 50 μM MeHg). Cholinergic degeneration was observed in all groups co-exposed to both metals. Notably, combined exposure to metals was more toxic to the worms than when exposed to a single metal.

Cadmium-induced serotonergic neuron and reproduction damages conferred lethality in the nematode Caenorhabditis elegans

Cadmium is a ubiquitous environmental toxicant. The use of Caenorhabditis elegans as a model for monitoring cadmium exposure has revealed several conserved signaling pathways. However, little is known about the killing process during lethality assay. In the present study, we investigated the effects serotonergic neuronal and reproductive damages on cadmium exposure in C. elegans. We found that sterile hermaphrodites, males and worms that passed reproduction span presented high cadmium resistance compared to those of young adults. The results demonstrated that reproduction process other than reproduction capacity conferred cadmium sensitivity. Cadmium exposure resulted in high ratio bagging phenotype, which was a severe reproductive deficit with embryos hatched internally that could cause worms to die early. The mechanism of bagging formation was ascribed to cadmium-induced egg laying deficiency that led embryos to retain and hatch in uterus. The addition of serotonin and imipramine promoted egg laying and thereby increased cadmium resistance. The results demonstrated that vulval muscles responsible for egg laying were still functional, while the serotonergic hermaphrodite specific neurons might be dysfunctional under cadmium exposure. Cadmium exposure resulted in shrinkage of serotonergic neuronal body and reduced expressions of tryptophan hydroxylase, the key enzyme for serotonin synthesis. The protection of serotonergic neuron through transient thermal preconditioning improved survival rate. In conclusion, our study demonstrated that damages of serotonergic neurons and reproduction conferred to cadmium-induced lethality.

Overlooked Risks of Biochars: Persistent Free Radicals trigger Neurotoxicity in Caenorhabditis elegans

In recent years, biochars have gained increasing interest in mitigating climate changes and revitalizing contaminated or drained soil. Studies determining their impact on the ecosystem, especially on soil invertebrates, however, are still scarce and the neurotoxic potential of biochars has never been evaluated before. Using the model organism Caenorhabditis elegans we determined the neurotoxic effect of biochar produced from rice straw by pyrolysis at 500 °C at concentrations ranging from 0 to 2000 mg C·L^-1. Biochar had a hormetic effect on locomotion behavior. Furthermore, high concentrations impaired defecation as well as the recognition and response to a chemical attractant. None of the potential toxic chemicals in the biochar had sufficient high concentrations to explain the detected neurotoxic effect. Using electron paramagnetic resonance (EPR) spectroscopy, we detected free radicals in the biochar. Detrimental reaction of free radicals with biotic macromolecules can induce oxidative stress responses and are a potential reason for the evaluated neurotoxic effect of biochar. Overall, we were able to prove that biochars have the potential to act as weak neurotoxins to soil organisms and effects of persistent free radicals should be investigated further.