Sublethal Toxicity Endpoints of Heavy Metals to the Nematode Caenorhabditis elegans

Effects of hexavalent chromium on the biology of Steinernema feltiae: evaluating sublethal endpoints for ecotoxicity testing

Essential information about the effects of a pollutant on an ecosystem can be obtained by observing how it influences a bioindicator organism. Hexavalent chromium (Cr VI+) naturally occurs in Irish agricultural soils at levels of up to 250 mg/kg, which raises concerns about potential negative impacts on human health and the surrounding areas. This research aimed to assess the sublethal effect concentrations (up to 300 ppm) of Cr VI + on the entomopathogenic nematode (EPN) Steinernema feltiae focusing on endpoints such as nematode movement and host finding ability in contaminated sand and pathogenicity, percentage penetration, sex ratio and reproduction in Galleria mellonella. To achieve that, an Irish isolate of S. feltiae [strain SB 12 (1)], was used in all experiments. The attraction of nematodes to the insect host was tested using PVC tubes of various lengths, containing sand with various concentrations of Cr VI + (50-300 ppm in increments of 50). The replication was tenfold and the insect mortality was recorded at the end of the experiment. Results showed that there was a significant effect of Cr VI + on the pathogenicity, movement and host finding ability of the nematodes in contaminated sand, and on the percentage of penetration in an insect host. However, no significant effects among the studied Cr VI + concentrations were observed in S. feltiae reproduction in G. mellonella. Similarly, the presence of the toxicant (at low concentration of 12ppm) did not affect the growth of the nematode symbiotic bacteria in liquid and solid media (TSA and NBTA). Reproduction, unlike the other sublethal parameters tested, appeared not to be an optimal endpoint for assessing soil Cr VI + risk contamination. Overall, this study confirms the excellent potential of S. feltiae to be used as a suitable sentinel organism in assessing the risk of Cr VI + soil contamination especially in the contexts of agriculture and soil health.

Exploring the Sublethal Impacts of Cu and Zn on Daphnia magna: a transcriptomic perspective

Metal contamination of aquatic environments remains a major concern due to their persistence. The water flea Daphnia magna is an important model species for metal toxicity studies and water quality assessment. However, most research has focused on physiological endpoints such as mortality, growth, and reproduction in laboratory settings, as well as neglected toxicogenomic responses. Copper (Cu) and zinc (Zn) are essential trace elements that play crucial roles in many biological processes, including iron metabolism, connective tissue formation, neurotransmitter synthesis, DNA synthesis, and immune function. Excess amounts of these metals result in deviations from homeostasis and may induce toxic responses. In this study, we analyzed Daphnia magna transcriptomic responses to IC5 levels of Cu (120 µg/L) and Zn (300 µg/L) in environmental water obtained from a pristine lake with adjusted water hardness (150 mg/L CaCO3). The study was carried out to gain insights into the Cu and Zn regulated stress response mechanisms in Daphnia magna at transcriptome level. A total of 2,688 and 3,080 genes were found to be differentially expressed (DEG) between the control and Cu and the control and Zn, respectively. There were 1,793 differentially expressed genes in common for both Cu and Zn, whereas the number of unique DEGs for Cu and Zn were 895 and 1,287, respectively. Gene ontology and KEGG pathways enrichment were carried out to identify the molecular functions and biological processes affected by metal exposures. In addition to well-known biomarkers, novel targets for metal toxicity screening at the genomic level were identified.

Prominent toxicity of isocyanates and maleic anhydrides to Caenorhabditis elegans: Multilevel assay for typical organic additives of biodegradable plastics

Biodegradable plastics (BDP) are increasingly applied; however, there has been of concerns about their environmental safety, especially from nondegradable additive compositions. Until now, data of ecotoxicity of BDP additives is scarce. Here, nematode C. elegans was used to comparatively evaluate toxicity of an isocyanate additive, i.e., Hexamethylene diisocyanate (HDI), a maleic anhydride, i.e., Diallyl maleate (DIM), and other four BDP organic additives. These additives caused lethality of nematodes at µg L^-1 level, of lowest LC₅₀ value of HDI/DIM. Uniform exposure to these additives resulted in various degrees of inhibitions in body volumes and longevity, indicating developmental toxicity. Moreover, BDP additives induced significant elevations of gst-4 expression, especially mean 123.54 %/234.29 % increase in HDI/DIM group, but reduced ges-1 expression, which indicates oxidative damages and mitochondrial dysfunction. BDP additives further caused inhibition in locomotor and food intake/excretion behavior, and related damages of glutamatergic neurons and GABAergic neurons, indicating their neurotoxicity. We found HDI and DIM presented relatively strong effects on susceptible endpoints including lethality, gst-4, mean lifespan, food intake and excretion behavior. Overall, this study suggests prominent ecotoxic risk of isocyanates and maleic anhydrides as BDP additives, which is significant for the selection of environmentally friendly BDP additives.

Fosthiazate exposure induces oxidative stress, nerve damage, and reproductive disorders in nontarget nematodes

As a forceful nematicide, fosthiazate has been largely applied in the management of root-knot nematodes and other herbivorous nematodes. However, the toxicity of fosthiazate to nontarget nematodes is unclear. To explore the toxicity and the mechanisms of fosthiazate in nontarget nematodes, Caenorhabditis elegans was exposed to 0.01-10 mg/L fosthiazate. The results implied that treatment with fosthiazate at doses above 0.01 mg/L could cause injury to the growth, locomotion behavior, and reproduction of the nematodes. Moreover, L1 larvae were more vulnerable to fosthiazate exposure than L4 larvae. Reactive oxygen species (ROS) production and lipofuscin accumulation were fairly increased in 1 mg/L fosthiazate-exposed nematodes. Treatment with 0.1 mg/L fosthiazate significantly inhibited the activity of acetylcholinesterase (p < 0.01). Furthermore, subacute exposure to 10 mg/L fosthiazate strongly influenced the expression of genes related to oxidative stress, reproduction, and nerve function (e.g., gst-1, sod-1, puf-8, wee-1.3, and ace-1 genes). These findings suggested that oxidative stress, reproduction and nerve disorders could serve as key endpoints of toxicity induced by fosthiazate. The cyp-35a family gene was the main metabolic fosthiazate in C. elegans, and the cyp-35a5 subtype was the most sensitive, with a change in expression level of 2.11-fold compared with the control. These results indicate that oxidative stress and neurological and reproductive disorders played fundamental roles in the toxicity of fosthiazate in C. elegans and may affect the abundance and function of soil nematodes.

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 high-throughput microplate toxicity screening platform based on Caenorhabditis elegans

Caenorhabditis elegans (C. elegans), an established model organism, has been widely used in environmental toxicology research. However, most of the current toxicity testing methods based on worms are time-consuming. In this study we aimed to develop an automated and highly-integrated platform for high-throughput and in situ toxicity testing. Considering the superiority of C. elegans as a neurotoxicological model, this platform mainly evaluates general toxicology and neurotoxicology endpoints, which are usually induced by metals and pesticides, the major environmental contaminants. Microplates were used as a worm culturing system, which have good compatibility with any commercial microplate applicable instruments. We developed a microfluidic-based module for worm dispensing, and an image acquisition/analysis module for monitoring worms and detecting toxicity endpoints in bright filed. These were collectively incorporated with a commercial pipetting workstation for automated food/drug delivery and a high-content analysis system for fluorescence detection. The integrated platform achieved an efficient on-demand worm dispensing, long-term maintenance, regular monitoring and imaging, survival assay and behavioral analyses, and visualized gene reporter assay. Moreover, "Lab on Web" was achieved by connecting the platform to the web for remote operation, worm monitoring, and phenotype calculation. To demonstrate the ability of the platform for automated toxicity testing assays; worms were treated with cadmium and longevity, neurotoxicity, developmental toxicity and gst-4 expression were evaluated. We determined its feasibility and proposed the potential application in high-throughput toxicity screening for environmental risk assessment in the nearest future.

The intertwining between lead and ethanol in the model organism Caenorhabditis elegans

Caenorhabditis elegans (C. elegans) is a model organism widely used to evaluate the mechanistic aspects of toxicants with the potential to predict responses comparable to those of mammals. We report here the consequences of developmental lead (Pb) exposure on behavioral responses to ethanol (EtOH) in C. elegans. In addition, we present data on morphological alterations in the dopamine (DA) synapse and DA-dependent behaviors aimed to dissect the neurobiological mechanisms that underlie the relationship between these neurotoxicants. Finally, the escalation to superior animals that parallels the observed effects in both experimental models with references to EtOH metabolism and oxidative stress is also discussed. Overall, the literature revised here underpins the usefulness of C. elegans to evidence behavioral responses to a combination of neurotoxicants in mechanistic-orientated studies.

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.

Perfluorooctane sulfonate (PFOS) induces several behavioural defects in Caenorhabditis elegans that can also be transferred to the next generations

Perfluorooctane sulfonate (PFOS) is a well-known global persistent organic pollutant of grave concern to ecological and human health. Toxicity of PFOS to animals and humans are well studied. Although few studies have reported the behavioral effect of PFOS on nematode Caenorhabditis elegans, it's transgenerational effects were seldom studied. Therefore, we investigated the toxicity of PFOS on several behavioral responses besides bioaccumulation and transgenerational effects in C. elegans. In contrast to the several published studies, we used lower concentrations (0.5-1000 μg/L or 0.001-2.0 μM) that are environmentally relevant and reported to occur close to the contaminated areas. The 48 h median lethal concentration of PFOS was found to be 3.15 μM (1575 μg/L). PFOS (≥0.01 μM) caused severe toxicity to locomotion, and this effect was even transferred to progeny. However, after a few generations, the defect was rectified in the progeny of single-time exposed parent nematodes. Whereas, continuous exposure at 0.001 μM PFOS, no visible defects were observed in the progeny. PFOS (≥0.01 μM) also significantly decreased the brood size in a concentration-dependent manner. Besides, lifespan was affected by the higher concentration of PFOS (≥1.0 μM). These two behavioral endpoints, lifespan and reproduction defects, became less severe in the progeny. Chemotaxis plasticity was also significantly retarded by ≥ 1.0 μM PFOS compared to the control group. Results indicate that PFOS can exert severe neurobehavioral defects that can be transferred from parents to their offspring. The findings of this study have significant implications for the risk assessment of perfluorinated substances in the environment.

Using Caenorhabditis elegans to assess the ecological health risks of heavy metals in soil and sediments around Dabaoshan Mine, China

Heavy metal pollution is a global environmental problem, and the potential risks associated with heavy metals are increasing. The acid mine drainage (AMD) which is generated by mining activities at Dabaoshan Mine, the largest polymetallic mine in southern China, is harmful to local residents. A detailed regional survey of the ecological and human health risks of this polluted area is urgently needed. In this study, eight sediments and farmland samples were collected along the flow direction of tailing wastewater and Fandong Reservoir; the content of multiple heavy metals in these samples was determined by inductively coupled plasma mass spectrometry. The biological toxicity of water-soluble extracts from the samples was further assessed by referring to different endpoints of Caenorhabditis elegans (C. elegans). The relationship between specific heavy metals and biological toxicity was estimated by partial least squares regression. The results indicated that the risk of heavy metals in Dabaoshan mining area was very high (potential ecological risk index = 721.53) and was related to geographical location. In these samples, the carcinogenic risk (the probability that people are induced carcinogenic diseases or injuries when exposed to carcinogenic pollutants) of arsenic (As) for adults exceeded the standard value 1 × 10^-4 and indicated that As presented a high carcinogenic risk to adults, while the high risk of non-carcinogenic effects (the hazard degree of human exposure to non-carcinogenic pollutants) in children was related to lead exposure (hazard index = 1.24). In addition, the heavy metals at high concentration in the water-soluble fraction of sediment and farmland soil extracts, which might easily distribute within the water cycle, inhibited the survival rate and growth of C. elegans. Gene expression and enzymatic activity related to oxidative stress were increased and genes related to apoptosis and metallothionein were also affected. In conclusion, the results of chemical analysis and biological assays provided evidence on the toxicity of soil and sediment extracts in the Dabaoshan mining area and advocated the control and remediation of heavy metal pollution around Dabaoshan Mine.

Distillery wastewater detoxification and management through phytoremediation employing Ricinus communis L

This study aimed to assess the phytoremediation potential of Ricinus communis L. for heavy metals remediation via rhizospheric bacterial activities for distillery wastewater detoxification and management. Results revealed that distillery wastewater contained high levels of metals and other physico-chemical pollution parameters that could cause environmental pollution and aquatic toxicity. The identified bacterium produced several plant growth-promoting compounds including siderophores, ligninolytic enzymes, and indole acetic acid that resulted in nutrient enhancement and improved mineralization of metals in the plants during stress conditions. The bioconcentration factor (BCF) of all the metals examined were > 1, which showed that these metals are accumulating in the root, shoot, and leaves of Ricinus communis L. Most of the metals are stablised in the roots but Pb, Cd and Zn were translocated more to the shoorts (TC>1). The ability of Ricinus communis L. to grow in metals-containing distillery wastewater and reduce heavy metals and organic contaminants suggests that it can be used to provide an effective treatment of distillery wastewater. The use of Ricinus communis L. is an eco-friendly tool for the reduction of organometallic contamination and protecting agricultural land.

Biomass of the macrophyte remedies and detoxifies Cd(II) and Pb(II) in aqueous solution

Aquatic plants are considered to be important remedial agents in aquatic environments contaminated by metals. The Salvinia biloba macrophyte was evaluated in relation to its removal kinetics, adsorption capacity, and toxicology, aiming at its application in the removal of Cd⁺² and Pb⁺² ions from aqueous solutions. A batch-type system was used, in which the plants were cultivated in microcosms containing nutritive solution and metallic ions, stored in a controlled environment (pH, temperature, and luminosity). The removal kinetics consisted in the analysis of efficiency, varying the concentrations of the metals, and time of cultivation of plants in solution. To describe the process, adsorption isotherms were constructed with the equilibrium data, which were later adjusted to Langmuir and Freundlich models. The toxicological trial was performed by sub-acute exposure test of Caenorhabditis elegans nematode to phytoremediated solutions. The results highlight the remedial effect of the plant in solutions contaminated with both metals. The kinetic study demonstrated that the plant responds differently to metals, and physical-chemical and biological processes can be attributed to the removal of metals from the solution by the plant. The equilibrium time obtained was 48 h for both metals, and the adsorption capacity was higher for Cd²⁺. The toxicological evaluation indicates that there was a reduction in toxicity after the remediation of the solutions by S. biloba, for all times and concentrations evaluated. Salvinia biloba was efficient for the removal of Cd²⁺ and Pb²⁺ metals from aqueous solution. The plant is a low-cost metal biosorbent and can be considered promising for phytoremediation strategies in liquid effluents and water bodies.

N-acetylcysteine restores the cadmium toxicity of Caenorhabditis elegans

Cadmium is a well-known environmental toxicant. At the cellular level, exposure to cadmium results in cytotoxic effects through the elevation of reactive oxygen species (ROS) production. Although cadmium exposure leads to the dysfunction of various organs, the underlying mechanisms of the toxic effects of cadmium in vivo are still largely unknown. Caenorhabditis elegans (C. elegans) is a useful model animal and exhibits unique biological reactions in response to environmental toxicants. In this study, the toxic mechanisms of cadmium exposure in C. elegans were investigated using N-acetylcysteine (NAC), which has dual functions, i.e., as a chelator of metals and as an antioxidant. NAC did not inhibit the uptake of cadmium into nematodes, suggesting that NAC did not function as a chelator of cadmium under these experimental conditions. Based on this finding, we investigated the effect of NAC as an antioxidant on representative phenotypic traits caused by cadmium exposure-reduced body length, aversion behavior, and shortened lifespan. NAC did not reverse the decreased body size but did clearly restore the aversion behavior and the shortened lifespan. These data suggest that aversion behavior and shortened lifespan are mediated by oxidative stress in C. elegans.

Knock-down of transcription factor skinhead-1 exacerbates arsenite-induced oxidative damage in Caenorhabditis elegans

Transcription factor, skinhead-1 (skn-1) has been demonstrated to play central roles in regulation of oxidative damage. Arsenite is an oxidative damage inducer in the environment. However, the role of skn-1 in arsenite-induced oxidative damage remains unclear. Thus, in this study, by using RNAi feeding, different toxic responses of wild-type and skn-1 knockdown nematodes to arsenite were evaluated. Our results demonstrated that arsenite did not show any significant impacts on locomotory behaviors, but skn-1 knock-down worms were much more sensitive to arsenite treatment, manifested by an aggravated reduction of survival rate than that of wild-type nematodes. In arsenite-treated worms, down-regulation of skn-1 significantly exacerbated the arsenite-induced changed expressions of oxidative damage-related genes, xbp-1, apl-1 and trxr-2, but these regulated effects of skn-1 were not observed on spr-4 and sel-12 expressions under arsenite treatment. These findings together suggest that skn-1 may play a vital role in protection of C. elegans from arsenite-induced oxidative damage.

Bacterial degradation of distillery wastewater pollutants and their metabolites characterization and its toxicity evaluation by using Caenorhabditis elegans as terrestrial test models

Distillery wastewater has significant amount of coloring compounds and organic substances even after the secondary treatment process, which poses many severe environmental and health threats. However, the recalcitrant coloured compounds have not yet been clearly identified. In this study, two bacterial strains DS3 and DS5 capable to decolorize distillery wastewater (DWW) pollutants were isolated and characterized as Staphylococcus saprophyticus (MF182113) and Alcaligenaceae sp. (MF182114), respectively. Results showed that mixed bacterial culture was found more effective decolorizing 71.83% DWW compared to axenic culture DS3 and DS5 resulting only 47.94% and 50.67% decolorization, respectively. The FT-IR and LC-MS/MS analysis of untreated DWW showed the presence of many recalcitrant compounds having different functional groups, but after bacterial treatment, most of compounds get diminished and the toxicity of DWW was reduced significantly. Further, the Nile red staining of Caenorhabditis elegans exposed to untreated and bacteria treated DWW for evaluation of toxicity assay and results revealed that the worms exposed to untreated DWW showed sharp reduction in total fat content having more profound effects, suggesting the diminished nAchR signaling as compare to bacterial treated DWW. Hence, this study revealed that inadequate disposal of untreated DWW may cause transfer of toxic substances into the environment and receiving water bodies.

Revealing the anticancer potential of candidate drugs in vivo using Caenorhabditis elegans mutant strains

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Mutations in the Wnt, Notch, and Ras-ERK signaling pathways in C. elegans lead to infertility, sterility, and multivulva formation.

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Phenotypic assays using C. elegans mutant strains can be used as in vivo models for drug repurposing.

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Itraconazole, disulfiram, etodolac, and ouabain have anticancer potential that can specifically target the Wnt, Notch, and RAS-ERK signaling pathways.

Drug repurposing is used as a strategy for finding new drugs for cancer. The process is a faster and a more cost-effective way of providing new indications for drugs that can address emerging drug resistance and numerous side effects of chemotherapeutic drugs. In this study, the in vivo anticancer potential of itraconazole, disulfiram, etodolac, and ouabain were assessed using five different C. elegans mutant strains. Each strain contains mutations in genes involved in different signaling pathways such as Wnt (JK3476), Notch (JK1107 and BS3164), and Ras-ERK (SD939 and MT2124) that result to phenotypes of sterility, infertility, and multivulva formation. These same signaling pathways have been shown to be defective in several human cancer types. The four candidate drugs were tested on the C. elegans mutant strains to determine if they rescue the mutant phenotypes. Both ouabain and etodolac significantly reduced the sterile and infertile phenotypes of JK3476, JK1107, BS3164, and SD939 strains (p=0.0010). Finally, itraconazole and etodolac significantly reduced multivulva formation (p=0.0021). The degrees of significant phenotypic rescues of each mutant were significantly higher than vehicle only (1% DMSO). Therefore, this study demonstrated that the four candidate drugs have anticancer potential in vivo, and etodolac had the highest anticancer potential.

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.

Molecular genetic and biochemical characterization of a putative family of zinc metalloproteins in Caenorhabditis elegans

The first characterization of W08E12.2, W08E12.3, W08E12.4 and W08E12.5, four putative metalloproteins in C. elegans. (A) phase contrast microscopy, (B) fluorescence microscopy of PW08E12.3;W08E12.4::GFP.

Four highly similar genes (W08E12.2, W08E12.3, W08E12.4 and W08E12.5) which are consecutively aligned on chromosome IV of the C. elegans genome are predicted to code for small (120–141aa) yet cysteine rich (18–19 cysteines) proteins. Cloning and sequencing of the genomic regions of the isoforms confirmed the presence and order of all genes. The generation of transgenic worms strains with an integrated single copy or extrachromosomal multi-copy PW08E12.3;W08E12.4::GFP uncovered that W08E12.3 and W08E12.4 are constitutively expressed in the pharynx and significantly induced in worms exposed to 100 μM Zn. Knockdown by RNAi did not have a marked consequence on reproductive performance nor was a Zn-dependent effect on nematode growth observed. However, RNAi of these genes led to an accumulation of Zn in the intestinal cells. W08E12.3 was recombinantly expressed in E. coli and the purified protein was shown to be able to bind up to 6.5 Zn molecules at neutral pH. Zn-binding was acid-labile and the apo protein was observed at pH < 4.3. This characterization suggests W08E12.2, W08E12.3, W08E12.4 and W08E12.5 belong to a family of putative Metalloproteins which, akin to metallothioneins, may play an important role in Zn-sensing, homeostasis and/or detoxification.

Reprotoxicity of glyphosate-based formulation in Caenorhabditis elegans is not due to the active ingredient only

Pesticides guarantee us high productivity in agriculture, but the long-term costs have proved too high. Acute and chronic intoxication of humans and animals, contamination of soil, water and food are the consequences of the current demand and sales of these products. In addition, pesticides such as glyphosate are sold in commercial formulations which have inert ingredients, substances with unknown composition and proportion. Facing this scenario, toxicological studies that investigate the interaction between the active principle and the inert ingredients are necessary. The following work proposed comparative toxicology studies between glyphosate and its commercial formulation using the alternative model Caenorhabditis elegans. Worms were exposed to different concentrations of the active ingredient (glyphosate in monoisopropylamine salt) and its commercial formulation. Reproductive capacity was evaluated through brood size, morphological analysis of oocytes and through the MD701 strain (bcIs39), which allows the visualization of germ cells in apoptosis. In addition, the metal composition in the commercial formulation was analyzed by ICP-MS. Only the commercial formulation of glyphosate showed significant negative effects on brood size, body length, oocyte size, and the number of apoptotic cells. Metal analysis showed the presence of Hg, Fe, Mn, Cu, Zn, As, Cd and Pb in the commercial formulation, which did not cause reprotoxicity at the concentrations found. However, metals can bioaccumulate in soil and water and cause environmental impacts. Finally, we demonstrated that the addition of inert ingredients increased the toxic profile of the active ingredient glyphosate in C. elegans, which reinforces the need of components description in the product labels.

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.

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.

Transgenerational effects of diesel particulate matter on Caenorhabditis elegans through maternal and multigenerational exposure

Diesel particulate matter (DPM) is a dominant contaminant in fine particulate matters (PM_2.5) and has been proved to induce serious harmful effects to human beings, including lung cancer, allergic, and chronic bronchitis. However, little attention has been paid to understand the transgenerational effects of DPM. In the present study, we focused on the transgenerational effects of DPM in the model organism Caenorhabditis elegans (C. elegans) exposed in either maternal generation (F0) or consecutive generations (F0-F5). In maternal exposure manner, 0.1 and 1.0 µg/mL DPM significantly increased the germ cell apoptosis at F0 generation, while the number of apoptotic germ cells at F1-F5 generation were gradually recovered back to control level. The brood size were significantly reduced by DPM at F2 generation and recovered to control level at F3-F5 generations. In continuous exposure manner, although 0.1 and 1.0 µg/mL DPM induced significant germ cell apoptosis in F0 generation, there was no difference between F0 and other generations. Continuous exposure to DPM at 0.1 and 1.0 µg/mL impaired the brood size in F2 to F5 generations. Using a series of loss-of-function mutant strains, we found that cep-1 (w40), hus-1 (op241), and mitogen-activated protein kinase (MAPK) related signaling pathway genes were involved in DPM-induced apoptosis. Our results clearly demonstrated that the adverse effects of DPM could be passed on through long-term multigenerational exposure and DNA damage checkpoint genes and MAPK signal pathway played an essential role in response to DPM induced development and reproduction toxicity.

Heavy metals immobilization capability of two iron-based nanoparticles (nZVI and Fe3O4): Soil and freshwater bioassays to assess ecotoxicological impact

The contamination by heavy metals constitutes an environmental problem of great importance in the last decades, and demands of society for clean environments are increasingly evident. To achieve this goal, several strategies have appeared for the in situ remediation of soil contamination caused by heavy metals. This study evaluated two types of iron-based nanoparticles, zero-valent iron nanoparticles (nZVI) and Fe₃O₄ nanoparticles, for the effective immobilization of Furthermore, we conducted a set of ecotoxicological bioassays: Microtox® Test, Caenorhabditis elegans Test, and Phytoplankton Toxicity Tests, on selected soil and aquatic test organisms to both, i) evaluate the potential ecotoxicological risks associated with nanoparticles treatment, and ii) to define sensitive organisms to be used as suitable bioindicators of heavy metals pollution. The application of 5% nZVI significantly reduced the amount of bioavailable heavy metals, which was effective from an ecotoxicity point of view as a reduction of the toxicity of was observed. Among the bioassays used, C. elegans seems the most effective reference organism in detecting changes in the toxicity of and therefore, C. elegans was found to be a sensitive heavy metals pollution bioindicator. When the Combination index (CI) was obtained to determine combined heavy metals interactions, the results indicated that toxicity would be higher than that expected for Pb, Cd and Zn individually considered, due to the proved antagonistic interactions of those toxicants. The obtained results suggested that nZVI nanoparticles are susceptible to be used as a soil remediation strategy for heavy metal pollution, although a short reactive lifespan must be considered, and therefore its effectiveness in long periods remains to be elucidated.

Circular Estimate Method (CEM) - a Simple Method to Estimate Caenorhabditis elegans Culture Densities in Liquid Medium

Background

Nematodes are used in many different fields of science, including environmental and biomedical research. Counting and/or estimating nematode numbers is required during research. Although being one of the most common procedures, this apparently simple task is a time-consuming process, prone to errors and concerns regarding procedure, reliability, and accuracy. When an estimate is necessary, there is a traditional manual counting procedure that in this study it will be called as "drop method" (DM). This popular method that extrapolates an animal count from a small drop of fluid shows a high coefficient of variation. To solve this problem, the present study used the free-living nematode Caenorhabditis elegans to develop a new estimation procedure that was based on a relationship between area and volume of a larger sample.

Results

The new method showed a low coefficient of variation and a close relationship between estimated and real counts of the total number of nematodes in large C. elegans suspensions. Reactive oxygen concentration was measured as an example of method application and to allow comparison between methods.

Conclusion

The proposed method is accurate, facile and reproducible, requiring simple, inexpensive materials that make it an excellent alternative to the DM manual counting procedure. Although the DM is faster, its estimates are not as accurate or as precise as those of the new proposed method.

Stabilization of Cd-, Pb-, Cu- and Zn-contaminated calcareous agricultural soil using red mud: a field experiment

Red mud (RM) was used to remediate heavy metal-contaminated soils. Experiments with two different dosages of RM added to soils were carried out in this study. It was found that soil pH increased 0.3 and 0.5 unit with the dosage of 3 and 5% (wt%), respectively. At the dosage of 5%, the highest stabilization efficiencies for Cd, Pb, Cu and Zn reached 67.95, 64.21, 43.73 and 63.73%, respectively. The addition of RM obviously transferred Cd from the exchangeable fraction to the residual fraction. Meanwhile, in comparison with the control (no RM added), it reduced 24.38, 49.20, 19.42 and 8.89% of Cd, Pb, Cu and Zn in wheat grains at the RM addition dosage of 5%, respectively. At the same time, the yield of wheat grains increased 17.81 and 24.66% at the RM addition dosage of 3 and 5%, respectively. Finally, the addition of RM did not change the soil bacterial community. These results indicate that RM has a great potential in stabilizing heavy metals in calcareous agricultural soils.

Exploiting the unique phenotypes of the earthworm Eudrilus eugeniae to evaluate the toxicity of chemical substances

Both the evaluation and the determination of toxicity of chemical substances present in the environment have implications in human health. In this present study, the natural phenomenon named autotomy, a self-defense mechanism employed by several animals against the toxic chemical contaminants, was considered to assess the toxicity of different chemical substances. We investigated the effects of glucose, sodium chloride, kanamycin, mercuric chloride, arsenic trioxide, and lead oxide on the phenotypes of earthworm Eudrilus eugeniae. Depending on the concentration of different chemicals, worms exhibit unique phenotypes. These phenotypes can be used to identify the toxicity as well as the toxic concentration of the chemicals. Upon exposure to toxic chemicals, worms use different mechanical forces at the site of cleavage furrow to detach its segments. During the detachment, there is no apparent blood loss at both the ends of the worm. Our results show that the mercuric chloride is toxic at the concentration above 5 μg when compared to other chemicals. Based on our findings, the toxic effects of a chemical and the toxic concentration of a chemical can be evaluated in both cost and time-efficient manner; in addition, these chemicals can be classified into the following categories: (1) mercuric chloride is extreme-toxic, (2) arsenic trioxide and lead oxide is toxic, (3) kanamycin and sodium chloride is low-toxic, and (4) glucose is non-toxic.

Neurodegeneration Induced by Metals in Caenorhabditis elegans

Metals are a component of a variety of ecosystems and organisms. They can generally be divided into essential and nonessential metals. The essential metals are involved in physiological processes once the deficiency of these metals has been associated with diseases. Although iron, manganese, copper, and zinc are important for life, it has been evidenced that they are also involved in neuronal damage in many neurodegenerative disorders. Nonessential metals, which are metals without physiological functions, are present in trace or higher levels in living organisms. Occupational, environmental, or deliberate exposures to lead, mercury, aluminum, and cadmium are clearly correlated with the increase of toxicity and varied kinds of pathological situations. Actually, the field of neurotoxicology needs to satisfy two opposing demands: the testing of a growing list of chemicals and resource limitations and ethical concerns associated with testing using traditional mammalian species. Toxicological assays using alternative animal models may relieve some of this pressure by allowing testing of more compounds while reducing expenses and using fewer mammals. The nervous system is by far the more complex system in C. elegans. Almost a third of their cells are neurons (302 neurons versus 959 cells in adult hermaphrodite). It initially underwent extensive development as a model organism in order to study the nervous system, and its neuronal lineage and the complete wiring diagram of its nervous system are stereotyped and fully described. The neurotransmission systems are phylogenetically conserved from nematodes to vertebrates, which allows for findings from C. elegans to be extrapolated and further confirmed in vertebrate systems. Different strains of C. elegans offer a new perspective on neurodegenerative processes. Some genes have been found to be related to neurodegeneration induced by metals. Studying these interactions may be an effective tool to slow neuronal loss and deterioration.

The nematode Caenorhabditis elegans as an integrated toxicological tool to assess water quality and pollution

Determination of water quality status in rivers is critical to establish a sustainable water management policy. For this reason, over the last decades it has been recommended to perform integrated water assessments that include water quantities and physicochemical, ecological and toxicological tests. However, sometimes resources are limited and it is not possible to perform large-scale chemical determinations of pollutants or conduct numerous ecotoxicological tests. To overcome this problem we use and measure the growth, as a response parameter, of the soil nematode Caenorhabditis elegans to assess water quality in rivers. The C. elegans is a ubiquitous organism that has emerged as an important model organism in aquatic and soil toxicology research. The Tunuyán River Basin (Province of Mendoza, Argentina) has been selected as a representative traditional water monitoring system to test the applicability of the C. elegans toxicological bioassay to generate an integrated water quality evaluation. Jointly with the C. elegans toxic assays, physicochemical and bacteriological parameters were determined for each monitoring site. C. elegans bioassays help to identify different water qualities in the river basin. Multivariate statistical analysis (PCA and linear regression models) has allowed us to confirm that traditional water quality studies do not predict potential toxic effects on living organisms. On the contrary, physicochemical and bacteriological analyzes explain <62% of the C. elegans growth response variability, showing that ecotoxicological bioassays are important to obtain a realistic scenario of water quality threats. Our results confirm that the C. elegans bioassay is a sensible and suitable tool to assess toxicity and should be implemented in routine water quality monitoring.

Transgenerational Reproductive Effects of Arsenite Are Associated with H3K4 Dimethylation and SPR-5 Downregulation in Caenorhabditis elegans

Arsenic is a prevalent environmental toxin. Arsenic is associated with a wide variety of adverse effects; however, studies on whether As-induced toxicities can be transferred from parents to offspring have received little attention. Caenorhabditis elegans has become an important animal model in biomedical and environmental toxicology research. In this study, transgenerational reproductive toxicity by arsenite exposure and the underlying mechanisms in C. elegans were investigated over six generations (F0-F5). Following arsenite maternal exposure of the F0 generation, subsequent generations (F1-F5) were cultured under arsenite-free conditions. We found that the brood size of C. elegans was significantly reduced by arsenite exposure in F0 and that this reduction in brood size was also observed in the offspring generations (F1-F5), after the toxicant had been removed from the diet. In addition, adult worms from F0 and F1 generations accumulated arsenite and arsenate when F0 L4 larvae were exposed to arsenite for 24 h. We found that the mRNA level of H3K4me2 demethylase LSD/KDM1, spr-5, was significantly reduced in the F0 exposed generation and subsequent unexposed generations (F1-F3). Likewise, the mRNA levels of spr-5 were also significantly decreased in the F1-F3 generations. Moreover, dimethylation of global H3K4 was increased in the F0-F3 generations. Our study demonstrates that maternal arsenite exposure causes transgenerational reproductive effects in C. elegans, which might be associated with H3K4 dimethylation and SPR-5 downregulation.

Internal Concentration and Time Are Important Modifiers of Toxicity: The Case of Chlorpyrifos on Caenorhabditis elegans

The internal concentration of chemicals in exposed organisms changes over time due to absorption, distribution, metabolism, and excretion processes since chemicals are taken up from the environment. Internal concentration and time are very important modifiers of toxicity when biomarkers are used to evaluate the potential hazards and risks of environmental pollutants. In this study, the responses of molecular biomarkers, and the fate of chemicals in the body, were comprehensively investigated to determine cause-and-effect relationships over time. Chlorpyrifos (CP) was selected as a model chemical, and Caenorhabditis elegans was exposed to CP for 4 h using the passive dosing method. Worms were then monitored in fresh medium during a 48-h recovery regime. The mRNA expression of genes related to CYP metabolism (cyp35a2 and cyp35a3) increased during the constant exposure phase. The body residue of CP decreased once it reached a peak level during the early stage of exposure, indicating that the initial uptake of CP rapidly induced biotransformation with the synthesis of new CYP metabolic proteins. The residual chlorpyrifos-oxon concentration, an acetylcholinesterase (AChE) inhibitor, continuously increased even after the recovery regime started. These delayed toxicokinetics seem to be important for the extension of AChE inhibition for up to 9 h after the start of the recovery regime. Comprehensive investigation into the molecular initiation events and changes in the internal concentrations of chemical species provide insight into response causality within the framework of an adverse outcome pathway.