Dynamic energy-based modeling of uranium and cadmium joint toxicity to Caenorhabditis elegans

Extrapolation of Metal Toxicity Data for the Rotifer Brachionus calyciflorus Using an Individual-Based Population Model

Ecological risk assessment (ERA) of metals typically starts from standardized toxicity tests, the data from which are then extrapolated to derive safe concentrations for the envisioned protection goals. Because such extrapolation in conventional ERA lacks ecological realism, ecological modeling is considered as a promising new approach for extrapolation. Many published population models are complex, that is, they include many processes and parameters, and thus require an extensive dataset to calibrate. In the present study, we investigated how individual-based models based on a reduced version of the Dynamic Energy Budget theory (DEBkiss IBM) could be applied for metal effects on the rotifer Brachionus calyciflorus. Data on survival over time and reproduction at different temperatures and food conditions were used to calibrate and evaluate the model for copper effects. While population growth and decline were well predicted, the underprediction of population density and the mismatch in the onset of copper effects were attributed to the simplicity of the approach. The DEBkiss IBM was applied to toxicity datasets for copper, nickel, and zinc. Predicted effect concentrations for these metals based on the maximum population growth rate were between 0.7 and 3 times higher in all but one case (10 times higher) than effect concentrations based on the toxicity data. The size of the difference depended on certain characteristics of the toxicity data: both the steepness of the concentration-effect curve and the relative sensitivity of lethal and sublethal effects played a role. Overall, the present study is an example of how a population model with reduced complexity can be useful for metal ERA. Environ Toxicol Chem 2024;43:324-337. © 2023 SETAC.

Sublethal effects of binary mixtures of Cu2+ and Cd2+ on Daphnia magna: Standard Dynamic Energy Budget (DEB) model analysis

Dynamic Energy Budget theory (DEB) describes mass and energy fluxes that occur in living organisms. DEB models were successfully used to assess the influence of stress, including toxic substances, and changes in pH and temperature, on different organisms. In this study, the Standard DEB model was used to evaluate the toxicity of copper and cadmium ions and their binary mixtures on Daphnia magna. Both metal ions have a significant influence on daphnia growth and reproduction. Different physiological modes of action (pMoA) were applied to primary DEB model parameters. Model predictions for chosen modes of interaction of mixture components were evaluated. The goodness of model fit and the model prediction was assessed to indicate the most likely pMoA and interaction mode. Copper and cadmium influence more than one DEB model primary parameter. Different pMoAs can result in similar model fits, and therefore it is difficult to identify pMoA only by evaluation of the goodness of fit of the model to the growth and reproduction data. Some critical discussion and ideas for model development are therefore provided.

A novel equal frequency sampling of factor levels (EFSFL) method is applied to identify the dominant factor inducing the combined toxicities of 13 factors

The research framework combining global sensitivity analysis (GSA) with quantitative high-throughput screening (qHTS), called GSA-qHTS, provides a potentially feasible way to screen for important factors that induce toxicities of complex mixtures. Despite its value, the mixture samples designed using the GSA-qHTS technique still have a shortage of unequal factor levels, which leads to an asymmetry in the importance of elementary effects (EEs). In this study, we developed a novel method for mixture design that enables equal frequency sampling of factor levels (called EFSFL) by optimizing both the trajectory number and the design and expansion of the starting points for the trajectory. The EFSFL has been successfully employed to design 168 mixtures of 13 factors (12 chemicals and time) that each have three levels. By means of high-throughput microplate toxicity analysis, the toxicity change rules of the mixtures are revealed. Based on EE analysis, the important factors affecting the toxicities of the mixtures are screened. It was found that erythromycin is the dominant factor and time is an important non-chemical factor in mixture toxicities. The mixtures can be classified into types A, B, and C mixtures according to their toxicities at 12 h, and all the types B and C mixtures contain erythromycin at the maximum concentration. The toxicities of the type B mixtures increase firstly over time (0.25 ∼ 9 h) and then decrease (12 h), while those of the type C mixtures consistently increase over time. Some type A mixtures produce stimulation that increases with time. With the present new approach to mixture design, the frequency of factor levels in mixture samples is equal. Consequently, the accuracy of screening important factors is improved based on the EE method, providing a new method for the study of mixture toxicity.

Co-contaminants of ethinylestradiol and sulfamethoxazole in groundwater exacerbate ecotoxicity and ecological risk and compromise the energy budget of C. elegans

Ethinylestradiol (EE2) and sulfamethoxazole (SMX) are among pharmaceuticals and personal care products (PPCPs) and regarded as emerging contaminants in groundwater worldwide. However, the ecotoxicity and potential risk of these co-contaminants remain unknown. We investigated the effects of early-life long-term co-exposure to EE2 and SMX in groundwater on life-history traits of Caenorhabditis elegans and determined potential ecological risks in groundwater. L1 larvae of wild-type N2 C. elegans were exposed to measured concentrations of EE2 (0.001, 0.75, 5.1, 11.8 mg/L) or SMX (0.001, 1, 10, 100 mg/L) or co-exposed to EE2 (0.75 mg/L, no observed adverse effect level derived from its reproductive toxicity) and SMX (0.001, 1, 10, 100 mg/L) in groundwater. Growth and reproduction were monitored on days 0 - 6 of the exposure period. Toxicological data were analyzed using DEBtox modeling to determine the physiological modes of action (pMoAs) and the predicted no-effect concentrations (PNECs) to estimate ecological risks posed by EE2 and SMX in global groundwater. Early-life EE2 exposure significantly inhibited the growth and reproduction of C. elegans, with lowest observed adverse effect levels (LOAELs) of 11.8 and 5.1 mg/L, respectively. SMX exposure impaired the reproductive capacity of C. elegans (LOAEL = 0.001 mg/L). Co-exposure to EE2 and SMX exacerbated ecotoxicity (LOAELs of 1 mg/L SMX for growth, and 0.001 mg/L SMX for reproduction). DEBtox modeling showed that the pMoAs were increased growth and reproduction costs for EE2 and increased reproduction costs for SMX. The derived PNEC falls within the range of detected environmental levels of EE2 and SMX in groundwater worldwide. The pMoAs for EE2 and SMX combined were increased growth and reproduction costs, resulting in lower energy threshold values than single exposure. Based on global groundwater contamination data and energy threshold values, we calculated risk quotients for EE2 (0.1 - 123.0), SMX (0.2 - 91.3), and combination of EE2 and SMX (0.4 - 341.1). Our findings found that co-contamination by EE2 and SMX exacerbates toxicity and ecological risk to non-target organisms, suggesting that the ecotoxicity and ecological risk of co-contaminants of pharmaceuticals should be considered to sustainably manage groundwater and aquatic ecosystems.

Modelling the effects of the pyrethroid insecticide cypermethrin on the life cycle of the soil dwelling annelid Enchytraeus crypticus, an original experimental design to calibrate a DEB-TKTD model

The Dynamic Energy Budget theory (DEB) enables ecotoxicologists to model the effects of chemical stressors on organism life cycles through the coupling of toxicokinetic-toxicodynamic (TK-TD) models. While good progress has been made in the application of DEB-TKTD models for aquatic organisms, applications for soil fauna are scarce, due to the lack of dedicated experimental designs suitable for collecting the required time series effect data. Enchytraeids (Annelida: Clitellata) are model organisms in soil ecology and ecotoxicology. They are recognised as indicators of biological activity in soil, and chemical stress in terrestrial ecosystems. Despite this, the application of DEB-TKTD models to investigate the impact of chemicals has not yet been tested on this family. Here we assessed the impact of the pyrethroid insecticide cypermethrin on the life cycle of Enchytraeus crypticus. We developed an original experimental design to collect the data required for the calibration of a DEB-TKTD model for this species. E. crypticus presented a slow initial growth phase that has been successfully simulated with the addition of a size-dependent food limitation for juveniles in the DEB model. The DEB-TKTD model simulations successfully agreed with the data for all endpoints and treatments over time. The highlighted physiological mode of action (pMoA) for cypermethrin was an increase of the growth energy cost. The threshold for effects on survival was estimated at 73.14 mg kg^- 1, and the threshold for effects on energy budget (i.e., sublethal effects) at 19.21 mg kg^- 1. This study demonstrates that DEB-TKTD models can be successfully applied to E. crypticus as a representative soil species, and may improve the ecological risk assessment for terrestrial ecosystems, and our mechanistic understanding of chemical effects on non-target species.

Nanoplastic exposure in soil compromises the energy budget of the soil nematode C. elegans and decreases reproductive fitness

Environmental nanoplastics (NPs) can accumulate in soils, posing a potential risk to soil ecosystems. However, the ecotoxicity of NPs for soil organisms has received little research attention. This study investigated whether NP exposure in soil leads to reproductive decline in the soil nematode Caenorhabditis elegans and sought to determine the mechanisms by which it may occur. Wild-type N2 C. elegans L1 larvae were exposed to various concentrations of nano-sized polystyrene (100 nm) in soil (0, 1, 10, 100, and 1000 mg/kg dry weight) for 96 h. We show that nano-sized polystyrene (100 nm) labeled with red fluorescence significantly accumulated in the intestine of C. elegans in a dose-dependent fashion via soil exposure (8%-47% increase). In addition, NP soil exposure led to 7%-33% decline in the number of eggs in utero and 2.6%-4.4% decline in the egg hatching percentage. We also find that the number of germ cell corpses (31%-55% increase) and the mRNA levels of germline apoptosis marker gene ced-3 (14%-31% increase) were significantly higher with greater NP soil exposure (10, 100, and 1000 mg/kg), while intracellular ATP levels were significantly reduced. Finally, the DEBtox model, which is based on the dynamic energy budget theory, was applied to show that the increased reproductive costs for C. elegans caused by NPs in soil are associated with energy depletion and reproductive decline. The threshold value (4.18 × 10^-6 mg/kg) for the energy budget also highlighted the potential high reproductive risk posed by NPs in terrestrial ecosystems. Our study provides new insights into how soil organisms interact with NPs in soil ecosystems.

Evaluation of the combined effect of elevated temperature and cadmium toxicity on Daphnia magna using a simplified DEBtox model

Thermal discharge and heatwaves under climate change may increase water temperature. In this study, the individual and combined effect of elevated temperature and cadmium (Cd) toxicity on somatic growth and reproduction of Daphnia magna was evaluated using a simplified dynamic energy budget model (DEBtox). The model predicted that the maximum body length (L_m) would be shorter (3.705 mm) at an elevated temperature of 25 °C than at 20 °C (3.974 mm), whereas the maximum reproduction rate (R˙_m) would be higher at 25 °C (5.735) than at 20 °C (5.591). The somatic growth and reproduction of D. magna were significantly (p < 0.05) reduced with increasing Cd concentrations, and the reduction was greater at 25 than at 20 °C. Potentiation of Cd toxicity by elevated temperature was correctly simulated by assuming four toxicological modes of action influencing assimilation, somatic maintenance and growth, and reproduction. Overall, the population growth rate of D. magna was expected to decrease linearly with increasing Cd concentrations, and the decrease was expected to be higher at 25 than at 20 °C. These findings suggest a significant ecological risk of toxic metals at elevated temperature, with a mechanistic interpretation of the potentiation effect using a DEBtox modeling approach.

What Is on the Outside Matters-Surface Charge and Dissolve Organic Matter Association Affect the Toxicity and Physiological Mode of Action of Polystyrene Nanoplastics to C. elegans

To better understand nanoplastic effects, the potential for surface functionalization and dissolve organic matter eco-corona formation to modify the mechanisms of action and toxicity of different nanoplastics needs to be established. Here, we assess how different surface charges modifying functionalization (postive (+ve) aminated; neutral unfunctionalized; negative (-ve) carboxylated) altered the toxicity of 50 and 60 nm polystyrene nanoplastics to the nematode Caenorhabditis elegans. The potency for effects on survival, growth, and reproduction reduced in the order +ve aminated > neutral unfunctionalized ≫ -ve carboxylated with toxicity >60-fold higher for the +ve than -ve charged forms. Toxicokinetic-toxicodynamic modeling (DEBtox) showed that the charge-related potency was primarily linked to differences in effect thresholds and dose-associated damage parameters, rather than to toxicokinetic parameters. This suggests that surface functionalization may change the nature of nanoplastic interactions with membrane and organelles leading to variations in toxicity. Eco-corona formation reduced the toxicity of all nanoplastics indicating that organic molecule associations may passivate surfaces. Between particles, eco-corona interactions resulting in more equivalent effects; however, even despite these changes, the order of potency of the charged forms was retained. These results have important implications for the development of future grouping approaches.

Bioenergetics modelling to analyse and predict the joint effects of multiple stressors: Meta-analysis and model corroboration

Understanding the consequences of the combined effects of multiple stressors-including stress from man-made chemicals-is important for conservation management, the ecological risk assessment of chemicals, and many other ecological applications. Our current ability to predict and analyse the joint effects of multiple stressors is insufficient to make the prospective risk assessment of chemicals more ecologically relevant because we lack a full understanding of how organisms respond to stress factors alone and in combination. Here, we describe a Dynamic Energy Budget (DEB) based bioenergetics model that predicts the potential effects of single or multiple natural and chemical stressors on life history traits. We demonstrate the plausibility of the model using a meta-analysis of 128 existing studies on freshwater invertebrates. We then validate our model by comparing its predictions for a combination of three stressors (i.e. chemical, temperature, and food availability) with new, independent experimental data on life history traits in the daphnid Ceriodaphnia dubia. We found that the model predictions are in agreement with observed growth curves and reproductive traits. To the best of our knowledge, this is the first time that the combined effects of three stress factors on life history traits observed in laboratory studies have been predicted successfully in invertebrates. We suggest that a re-analysis of existing studies on multiple stressors within the modelling framework outlined here will provide a robust null model for identifying stressor interactions, and expect that a better understanding of the underlying mechanisms will arise from these new analyses. Bioenergetics modelling could be applied more broadly to support environmental management decision making.

Impact of consumer-resource dynamics on C. elegans-E. coli system exposed to nano zero-valent iron (nZVI)

Nano zero-valent iron (nZVI) is one of the most paramount nanoparticles (NPs) applied in environmental remediation, leading to great concerns for the potential impacts on soil ecosystem health. The objective of this study was to link toxicokinetics and consumer-resource dynamics in the Caenorhabditis elegans-Escherichia coli (worm-bacteria) ecosystem. The biokinetic parameters of bacteria and worms were obtained from toxicokinetic experiments and related published literature. Biomass dynamics of bacteria and worms were estimated by employing the modified Lotka-Volterra model. Dynamics of bacteria and worm biomass, internal concentrations of nZVI, bioconcentration factors (BCFs), and biomagnification factors (BMFs) were simulated based on the consumer-resource dynamics. Results showed that the biomass of worms steadily increased from 22.25 to 291.49 g L^-1, whereas the biomass of bacteria decreased from 17.17 to 4.70 × 10^-8 g L^-1 after 96-h exposures of nZVI. We also observed ratios of nZVI concentrations in worms and bacteria increased from 0.06 to 26.60 after 96 h. Moreover, decrements of the bioconcentration factor of E. coli (BCF_E) values from 0.82 to 0.03 after 96 h were observed, whereas values of BMFs increased from 0.06 to 57.62 after 96 h. Internal concentrations of nZVI in worms were found to be mainly influenced by the ingestion rate of bacteria by worms, and the biomass conversion of bacteria had the lowest effect. Implementation of the integrated bioaccumulation-consumer-resource model supports the hypothesis that the C. elegans-E. coli dynamics of internal nZVI concentrations could be effectively associated with the predator-prey behavior and was dominated by the same physiological parameter in the two biological systems.

Higher than … or lower than ….? Evidence for the validity of the extrapolation of laboratory toxicity test results to predict the effects of chemicals and ionising radiation in the field

Single species laboratory tests and associated species sensitivity distributions (SSDs) that utilise the resulting data can make a key contribution to efforts to prospective hazard assessments for pesticides, biocides, metals and ionising radiation for research and regulatory risk assessment. An assumption that underlies the single species based toxicity testing approach when combined in SSD models is that the assessments of sensitivities to chemical and ionising radiation measured across a range of species in the laboratory can inform on the likely effects on communities present in the field. Potential issues with the validity of this assumption were already recognised by Van Straalen and Denneman (1989) in their landmark paper on the SSD methodology. In this work, they identified eight major factors that could potentially compromise the extrapolation of laboratory toxicity data to the field. Factors covered a range of issues related to differences in chemistry (e.g. bioavailability, mixtures); environmental conditions (optimal, variable), ecological (compensatory, time-scale) and population genetic structure (adaptation, meta-population dynamics). This paper outlines the evidence pertaining to the influence of these different factors on toxicity in the laboratory as compared to the field focussing especially on terrestrial ecosystems. Through radiological and ecotoxicological research, evidence of the influence of each factor on the translation of observed toxicity from the laboratory to field is available in all cases. The importance of some factors, such as differences in chemical bioavailability between laboratory tests and the field and the ubiquity of exposure to mixtures is clearly established and has some relevance to radiological protection. However, other factors such as the differences in test conditions (optimal vs sub-optimal) and the development of tolerance may be relevant on a case by case basis. When SSDs generated from laboratory tests have been used to predict chemical and ionising radiation effects in the field, results have indicated that they may often seem to under-predict impacts, although this may also be due to other factors such as the effects of other non-chemical stressors also affecting communities at polluted sites. A better understanding of the main factors affecting this extrapolation can help to reduce uncertainty during risk assessment.

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.

Dynamic energy budget models in ecological risk assessment: From principles to applications

In ecological risk assessment of chemicals, hazard identification and hazard characterisation are most often based on ecotoxicological tests and expressed as summary statistics such as No Observed Effect Concentrations or Lethal Concentration values and No Effect Concentrations. Considerable research is currently ongoing to further improve methodologies to take into account toxico kinetic aspects in toxicological assessments, extrapolations of toxic effects observed on individuals to population effects and combined effects of multiple chemicals effects. In this context, the principles of the Dynamic Energy Budget (DEB), namely the conserved allocation of energy to different life-supporting processes in a wide variety of different species, have been applied successfully to the development of a number of DEB models. DEB models allow the incorporation of effects on growth, reproduction and survival within one consistent framework. This review aims to discuss the principles of the DEB theory together with available DEB models, databases available and applications in ecological risk assessment of chemicals for a wide range of species and taxa. Future perspectives are also discussed with particular emphasis on ongoing research efforts to develop DEB models as open source tools to further support the research and regulatory community to integrate quantitative biology in ecotoxicological risk assessment.

Physiological modes of action across species and toxicants: the key to predictive ecotoxicology

As ecotoxicologists we strive for a better understanding of how chemicals affect our environment. Humanity needs tools to identify those combinations of man-made chemicals and organisms most likely to cause problems. In other words: which of the millions of species are at risk from pollution? And which of the tens of thousands of chemicals contribute most to the risk? We identified our poor knowledge on physiological modes of action (how a chemical affects the energy allocation in an organism), and how they vary across species and toxicants, as a major knowledge gap. We also find that the key to predictive ecotoxicology is the systematic, rigorous characterization of physiological modes of action because that will enable more powerful in vitro to in vivo toxicity extrapolation and in silico ecotoxicology. In the near future, we expect a step change in our ability to study physiological modes of action by improved, and partially automated, experimental methods. Once we have populated the matrix of species and toxicants with sufficient physiological mode of action data we can look for patterns, and from those patterns infer general rules, theory and models.

Ecological risk assessment of mixtures of radiological and chemical stressors: Methodology to implement an msPAF approach

A main challenge in ecological risk assessment is to account for the impact of multiple stressors. Nuclear facilities can release both radiological and chemical stressors in the environment. This study is the first to apply species sensitivity distribution (SSD) combined with mixture models (concentration addition (CA) and independent action (IA)) to derive an integrated proxy of the ecological impact of combined radiological and chemical stressors: msPAF (multisubstance potentially affected fraction of species). The approach was tested on the routine liquid effluents from nuclear power plants that contain both radioactive and stable chemicals. The SSD of ionising radiation was significantly flatter than the SSD of 8 stable chemicals (namely Cr, Cu, Ni, Pb, Zn, B, chlorides and sulphates). This difference in shape had strong implications for the selection of the appropriate mixture model: contrarily to the general expectations the IA model gave more conservative (higher msPAF) results than the CA model. The msPAF approach was further used to rank the relative potential impact of radiological versus chemical stressors.

Toxicity-based toxicokinetic/toxicodynamic assessment of bioaccumulation and nanotoxicity of zerovalent iron nanoparticles in Caenorhabditis elegans

Elucidating the relationships between the toxicity-based-toxicokinetic (TBTK)/toxicodynamic (TD) properties of engineered nanomaterials and their nanotoxicity is crucial for human health-risk analysis. Zerovalent iron (Fe⁰) nanoparticles (NPs) are one of the most prominent NPs applied in remediating contaminated soils and groundwater. However, there are concerns that Fe⁰NP application contributes to long-term environmental and human health impacts. The nematode Caenorhabditis elegans is a surrogate in vivo model that has been successfully applied to assess the potential nanotoxicity of these nanomaterials. Here we present a TBTK/TD approach to appraise bioaccumulation and nanotoxicity of Fe⁰NPs in C. elegans. Built on a present C. elegans bioassay with estimated TBTK/TD parameters, we found that average bioconcentration factors in C. elegans exposed to waterborne and food-borne Fe⁰NPs were ~50 and ~5×10^-3, respectively, whereas 10% inhibition concentrations for fertility, locomotion, and development, were 1.26 (95% CI 0.19-5.2), 3.84 (0.38-42), and 6.78 (2.58-21) μg·g^-1, respectively, implicating that fertility is the most sensitive endpoint in C. elegans. Our results also showed that biomagnification effects were not observed in waterborne or food-borne Fe⁰NP-exposed worms. We suggest that the TBTK/TD assessment for predicting NP-induced toxicity at different concentrations and conditions in C. elegans could enable rapid selection of nanomaterials that are more likely to be nontoxic in larger animals. We conclude that the use of the TBTK/TD scheme manipulating C. elegans could be used for rapid evaluation of in vivo toxicity of NPs or for drug screening in the field of nanomedicine.

Toxicokinetic models and related tools in environmental risk assessment of chemicals

Environmental risk assessment of chemicals for the protection of ecosystems integrity is a key regulatory and scientific research field which is undergoing constant development in modelling approaches and harmonisation with human risk assessment. This review focuses on state-of-the-art toxicokinetic tools and models that have been applied to terrestrial and aquatic species relevant to environmental risk assessment of chemicals. Both empirical and mechanistic toxicokinetic models are discussed using the results of extensive literature searches together with tools and software for their calibration and an overview of applications in environmental risk assessment. These include simple tools such as one-compartment models, multi-compartment models to physiologically-based toxicokinetic (PBTK) models, mostly available for aquatic species such as fish species and a number of chemical classes including plant protection products, metals, persistent organic pollutants, nanoparticles. Data gaps and further research needs are highlighted.

Integrated presentation of ecological risk from multiple stressors

Current environmental risk assessments (ERA) do not account explicitly for ecological factors (e.g. species composition, temperature or food availability) and multiple stressors. Assessing mixtures of chemical and ecological stressors is needed as well as accounting for variability in environmental conditions and uncertainty of data and models. Here we propose a novel probabilistic ERA framework to overcome these limitations, which focusses on visualising assessment outcomes by construct-ing and interpreting prevalence plots as a quantitative prediction of risk. Key components include environmental scenarios that integrate exposure and ecology, and ecological modelling of relevant endpoints to assess the effect of a combination of stressors. Our illustrative results demonstrate the importance of regional differences in environmental conditions and the confounding interactions of stressors. Using this framework and prevalence plots provides a risk-based approach that combines risk assessment and risk management in a meaningful way and presents a truly mechanistic alternative to the threshold approach. Even whilst research continues to improve the underlying models and data, regulators and decision makers can already use the framework and prevalence plots. The integration of multiple stressors, environmental conditions and variability makes ERA more relevant and realistic.

Benchmarking of protein carbonylation analysis in Caenorhabditis elegans: specific considerations and general advice

Oxidative stress has been extensively studied due to its correlation with cellular disorders and aging. In proteins, one biomarker of oxidative stress is the presence of carbonyl groups, such as aldehyde and ketone, in specific amino acid side chains such as lysine, proline, arginine and threonine, so-called protein carbonylation (PC). PC study is now a growing field in general and medical science since PC accumulation is associated with various pathologies and disorders. At present, enzyme-linked immunosorbent assays (ELISA) seem to be the most robust method of quantifying the presence of carbonyl groups in proteins, despite having some recognised caveats. In parallel, gel-based approaches present cross-comparison difficulties, along with other technical problems. As generic PC analyses still suffer from poor homogeneity, leading to cross-data analysis difficulties and poor results overlap, the need for harmonisation in the field of carbonyl detection is now widely accepted. This study aims to highlight some of the technical challenges in proteomic gel-based multiplexing experiments when dealing with PC in difficult samples like those from Caenorhabditis elegans, from protein extraction to carbonyl detection. We demonstrate that some critical technical parameters, such as labelling time, probe concentration, and total and carbonylated protein recovery rates, should be re-addressed in a sample-specific way. We also defined a procedure to cost-effectively adapt CyDye™-hydrazide-based protocols to specific samples, especially when the experimental interest is focused on studying differences between stimulating conditions with a maximised signal-to-noise ratio. Moreover, we have improved an already-existing powerful solubilisation buffer, making it potentially useful for hard-to-solubilise protein pellets. Lastly, the depicted methodology exemplifies a simple way of normalising carbonyl-related signal to total protein in SDS-PAGE multiplexing experiments. Within that scope, we also proposed a simple way to quantify carbonyl groups by on-gel spotting diluted dye-containing labelling buffer. Proof of the robustness of the procedure was also highlighted by the high linear correlation between the level of carbonyls and the ultraviolet exposure duration of whole worms (R²=0.993). Altogether, these results will help to standardise existing protocols in the growing field of proteomic carbonylation studies.