Key Opportunities to Replace, Reduce, and Refine Regulatory Fish Acute Toxicity Tests

Use of alternatives to animal testing for Environmental Safety Assessment (ESA): Report from the 2023 EPAA partners' forum

Environmental Safety Assessments (ESA) are mandatory for several regulatory purposes and are an important component of stewardship/sustainability initiatives. Fish testing is used for assessing chemical toxicity and bioaccumulation potential; amphibians are included in some jurisdictions and their use is increasing to assess endocrine disruption. Alternative methods are becoming more available, covering the principles of the 3Rs (i.e., replacing, reducing and refining animal tests), but their regulatory incorporation is still limited. A cross-sector review by the European Partnership for Alternative Approaches to Animal Testing (EPAA), discussed the status and priorities for accelerating the adoption of non-animal approaches in ESA. The lack of an internationally agreed definition for "animal testing" was recognized as a challenge. For example, testing with vertebrate embryos up to specific developmental stages is a suitable refinement alternative only in some jurisdictions. Invertebrate testing offers refinement alternatives to develop tiered approaches using vertebrate testing as a last resort. Aquatic ESA was identified as a common need by all sectors and regulatory areas, while terrestrial ESA is particularly relevant for agrochemicals. The standardization and validation of some alternative methods as OECD test guidelines (TGs) for fish acute toxicity and fish bioaccumulation have not yet triggered the expected replacement in regulatory settings. Priority actions in these areas are needed to generate confidence in the regulatory use of the available OECD TGs designed as alternatives, including the identification of applicability domains and guidance/decision-trees for integrating different lines of evidence. Case studies under the OECD Integrated Approaches to Testing and Assessment (IATA) program could facilitate further global regulatory uptake. Replacement of fish chronic toxicity testing is more complex and less advanced. A dual approach was suggested, in the short-term, exploring lines of evidence that, alone or in combination, could identify when further fish testing is not needed. The second phase should focus on the application of the 3Rs in those cases where chronic information is needed. Another area of increasing interest is endocrine disruption. It represents a challenge but also an opportunity for implementing mechanistic non-animal methods, in addition to integrate human and ESA. This requires a step-by-step approach with continuous dialogue to ensure that technical developments will address regulatory needs. The review also agreed that the long-term aspiration is a new ESA paradigm, mapping the protection goals and providing connectivity between the chemical legislation and environmental protection policies.

Explainable machine learning models for predicting the acute toxicity of pesticides to sheepshead minnow (Cyprinodon variegatus)

A quantitative structure-activity relationship (QSAR) study was conducted on 313 pesticides to predict their acute toxicity to Sheepshead minnow (Cyprinodon variegatus) by using DRAGON descriptors. Essentials accounting for a reliable model were all considered carefully, giving full consideration to the OECD (Organization for Economic Co-operation and Development) principles for QSAR acceptability in regulation during the model construction and assessment process. Nine variables were selected through the forward stepwise regression method and used as inputs to construct both linear and nonlinear models. The obtained models were validated internally and externally. Generally, machine learning-based methods, namely support vector machine (SVM), random forest (RF), and projection pursuit regression (PPR), perform better than the multiple linear regression (MLR) model. The statistical results (R2 = 0.682-0.933, Q2LOO = 0.604-0.659, Q2F1 = 0.740-0.796, CCC = 0.861-0.882) of the developed models show that they are robust, reliable, reproducible, accurate and predictive. Comparatively, the RF model performs best, giving predictive correlation coefficient Q2 of 0.814, root mean squared error (RMSE) of 0.658 and mean absolute error (MAE) of 0.534 for the test set, respectively. The RF model (as well as SVM and PPR models) was visualized and explained by using the SHapley Additive explanation (SHAP) analysis to enhance its transparency and credibility. In addition, the applicability domain (AD) range of the RF model was characterized by the Williams plot and the tree manifold approximation and projection (TMAP) technology was utilized to illustrate similarity and diversity of the entire data space, to assist in the analysis of the outliers. Activity cliff detection was investigated by using Arithmetic Residuals in K-groups Analysis (ARKA) descriptors. It was found that none of the pesticides was identified as an activity cliff in the training set or a potential prediction cliff in the test set. Therefore, the RF model fulfills each OECD principle in regulation for QSAR models. The research in this work will aid in the in silico QSAR prediction of the acute toxicity to Sheepshead minnow (Cyprinodon variegatus) for untested and new toxic pesticides and can also be extended to other studies.

A novel integrated testing strategy (ITS) for evaluating acute fish toxicity with new approach methodologies (NAMs)

Acute fish toxicity (AFT) tests are performed in aquatic risk assessments of chemical compounds globally. However, the specific endpoint of in vivo AFT is based on the lethal concentration 50 (LC50), which is a serious challenge in terms of animal welfare. To support the 3Rs principle of replacing, reducing, and refining use of animals, integrated testing strategies (ITS) have recently been developed for environmental risk assessment. ITS efficiently integrates multiple types of information, especially new approach methodologies (NAMs), and further supports regulatory decision-making. Currently, an effective ITS framework for evaluating aquatic toxicity is lacking. Therefore, we aimed to develop a promising ITS for AFT using in silico, in vitro, and in vivo data. We established the ITS via in silico (OECD QSAR Toolbox 4.6), fish cell line acute toxicity (FCT), and fish embryo acute toxicity (FET) tests and then validated the NAMs with AFT testing. The NAM data were derived from the European Chemicals Agency (ECHA) dossier, toxicology databases, peer-reviewed research articles, and this study. For the first step in the ITS process, we aimed to design a high-throughput screening tool to identify non-toxic and toxic chemicals. We found that results of in silico, FCT, and FET tests alone were strongly correlated with AFT. Among the models, the in silico model was most suitable for identifying toxicants due to its high sensitivity and minimal animal use. Next, considering regulatory purposes and flexibility, we determined the predictive LC50 of toxic chemicals by pursuing a preference-dependent strategy, sequential testing strategy, and sensitivity-dependent strategy. All the strategies demonstrated a predictive power equal to or greater than 73%. In addition, to meet user preferences, our ITS approach has high flexibility and supports animal welfare and environmental protection. We have therefore developed multiple powerful, flexible, and more humane ITS methods for acute fish toxicity assessment by integrating NAMs.

Establishment and identification of the head kidney cell line of yellowfin seabream (Acanthopagrus latus) and its application in a virus susceptibility study

The yellowfin seabream (Acanthopagrus latus) is a crucial marine resource owing to its economic significance. Acanthopagrus latus aquaculture faces numerous challenges from viral diseases, but a robust in-vitro research model to understand and address these threats is lacking. Therefore, we developed a novel A. latus cell line from head kidney cells called ALHK1. This study details the development, characterisation, and viral susceptibility properties of ALHK cells. This cell line primarily comprises fibroblast-like cells and has robust proliferative capacity when cultured at 28 °C in Leibovitz's L-15 medium supplemented with 10-20% foetal bovine serum. It exhibited remarkable stability after more than 60 consecutive passages and validation through cryopreservation techniques. The specificity of the ALHK cell line's origin from A. latus was confirmed via polymerase chain reaction (PCR) amplification of the cytochrome B gene, and a chromosomal karyotype analysis revealed a diploid count of 48 (2n = 48). Furthermore, the lipofection-mediated transfection efficiency using the pEGFP-N3 plasmid was high, at nearly 40%, suggesting that ALHK cells could be used for studies involving exogenous gene manipulation. In addition, ALHK cells displayed heightened sensitivity to the large mouth bass virus (LMBV), substantiated through observations of cytopathic effects, quantitative real-time PCR, and viral titration assays. Finally, the response of ALHK cells to LMBV infection resulted in differentially expressed antiviral genes associated with innate immunity. In conclusion, the ALHK cell line is a dependable in-vitro platform for elucidating the mechanisms of viral diseases in yellowfin seabream. Moreover, this cell line could be valuable for immunology, vaccine development, and host-pathogen interaction studies.

Isolation and characterisation of two epithelial-like cell lines from the gills of Chrysophrys auratus (Australasian snapper) and Oncorhynchus tshawytscha (Chinook salmon) and their use in aquatic toxicology

In vitro gill models are becoming increasingly important in aquatic toxicology, yet the fish gill invitrome is underrepresented, encompassing approximately 0.1% of extant species. Here, we describe the establishment and characterisation of two gill-derived, epithelial-like cell lines isolated from fish species of significant importance to New Zealand: Chrysophrys auratus (Australasian snapper) and Oncorhynchus tshawytscha (Chinook salmon). Designated CAgill1PFR (Chrysophrys auratus, gill 1, Plant & Food Research) and OTgill1PFR (Oncorhynchus tshawytscha, gill 1, Plant & Food Research), these cell lines have each been passaged greater than each 70 times over several years and are considered spontaneously immortalised. Both cell lines required serum for growth and exhibited differential responses to basal media formulations. CAgill1PFR was sensitive to low temperatures (4 °C) but replicated at high temperatures (30 °C), whereas OTgill1PFR was sensitive to high temperatures but remained viable at low temperatures, mirroring the natural environment of their host species. Immunostaining revealed expression of epithelial cell markers cytokeratin and E-cadherin, alongside positivity for the mesenchymal cell marker, vimentin. CAgill1PFR was more sensitive to the environmental toxin 3,4 dichloroaniline than OTgill1PFR through measurements of metabolic activity, membrane integrity, and lysosomal function. Furthermore, CAgill1PFR produced less CYP1A activity, indicative of ongoing biotransformation processes, in response to beta-naphthoflavone than OTgill1PFR. These cell lines expand the toolbox of resources and emphasise the need for species-specific aquatic toxicology research.

Fish acute toxicity of nine nanomaterials: Need of pre-tests to ensure comparability and reuse of data

Fish acute toxicity tests are commonly used in aquatic environmental risk assessments, being required in different international substances regulations. A general trend in the toxicity testing of nanomaterials (NMs) has been to use standardized aquatic toxicity tests. However, as these tests were primarily developed for soluble chemical, issues regarding particle dissolution, agglomeration or sedimentation during the time of exposure are not considered when reporting the toxicity of NMs. The aim of this study was to characterize the NM behaviour throughout the fish acute test and to provide criteria to assay the toxicity of nine NMs based on TiO2, ZnO, SiO2, BaSO4, bentonite, and carbon nanotubes, on rainbow trout following OECD Test Guideline (TG) nº203. Our results showed the importance of conducting a preliminary test (without fish) when working with NMs. They provide valuable information on, sample monitoring, agglomeration, sedimentation, dissolution, actual concentrations of NMs, needed to design the test. Among the NMs tested, only bentonite nanoparticles were stable during the 96-h pre-test and test in aquarium water. In contrast, the remaining NMs exhibited considerable loss and sedimentation within the first 24 h. The high sedimentation observed for almost all NMs highlights the need of consistently measuring the concentrations throughout the entire duration of the fish acute toxicity test to make reliable concentration-response relationships. Notable differences emerged in LC50 values when using actual concentrations as nominal concentrations overestimated concentrations by up to 85.6%. Among all NMs tested, only ZnO NMs were toxic to rainbow trout. A flow chart was specifically developed for OECD TG 203, aiding users in making informed decisions regarding the selection of test systems and necessary modifications to ensure accurate, reliable, and reusable toxicity data. Our findings might contribute to the harmonization of TG 203 improving result reproducibility and interpretability and supporting the development of read-across and QSAR models.

Big Question to Developing Solutions: A Decade of Progress in the Development of Aquatic New Approach Methodologies from 2012 to 2022

In 2012, 20 key questions related to hazard and exposure assessment and environmental and health risks of pharmaceuticals and personal care products in the natural environment were identified. A decade later, this article examines the current level of knowledge around one of the lowest-ranking questions at that time, number 19: "Can nonanimal testing methods be developed that will provide equivalent or better hazard data compared with current in vivo methods?" The inclusion of alternative methods that replace, reduce, or refine animal testing within the regulatory context of risk and hazard assessment of chemicals generally faces many hurdles, although this varies both by organism (human-centric vs. other), sector, and geographical region or country. Focusing on the past 10 years, only works that might reasonably be considered to contribute to advancements in the field of aquatic environmental risk assessment are highlighted. Particular attention is paid to methods of contemporary interest and importance, representing progress in (1) the development of methods which provide equivalent or better data compared with current in vivo methods such as bioaccumulation, (2) weight of evidence, or (3) -omic-based applications. Evolution and convergence of these risk assessment areas offer the basis for fundamental frameshifts in how data are collated and used for the protection of taxa across the breadth of the aquatic environment. Looking to the future, we are at a tipping point, with a need for a global and inclusive approach to establish consensus. Bringing together these methods (both new and old) for regulatory assessment and decision-making will require a concerted effort and orchestration. Environ Toxicol Chem 2024;43:559-574. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Weight of evidence tools in the prediction of acute fish toxicity

Acute fish toxicity (AFT) is a key endpoint in nearly all regulatory implementations of environmental hazard assessments of chemicals globally. Although it is an early tier assay, the AFT assay is complex and uses many juvenile fish each year for the registration and assessment of chemicals. Thus, it is imperative to seek animal alternative approaches to replace or reduce animal use for environmental hazard assessments. A Bayesian Network (BN) model has been developed that brings together a suite of lines of evidence (LoEs) to produce a probabilistic estimate of AFT without the testing of additional juvenile fish. Lines of evidence include chemical descriptors, mode of action (MoA) assignment, knowledge of algal and daphnid acute toxicity, and animal alternative assays such as fish embryo tests and in vitro fish assays (e.g., gill cytotoxicity). The effort also includes retrieval, assessment, and curation of quality acute fish toxicity data because these act as the baseline of comparison with model outputs. An ideal outcome of this effort would be to have global applicability, acceptance and uptake, relevance to predominant fish species used in chemical assessments, be expandable to allow incorporation of future knowledge, and data to be publicly available. The BN model can be conceived as having incorporated principles of tiered assessment and whose outcomes will be directed by the available evidence in combination with prior information. We demonstrate that, as additional evidence is included in the prediction of a given chemical's ecotoxicity profile, both the accuracy and the precision of the predicted AFT can increase. Ultimately an improved environmental hazard assessment will be achieved. Integr Environ Assess Manag 2023;19:1220-1234. © 2022 SETAC.

Defining piscine endpoints: Towards score sheets for assessment of clinical signs in fish research

The seminar 'Severity and humane endpoints in fish research' organized by the University of Bergen, the Industrial and Aquatic Laboratory, together with Fondazione Guido Bernadini, took place on 4 October 2019 in Bergen, Norway. The seminar was followed by a workshop, 'Establishing score sheets and defining endpoints in fish experiments', held on 28 January 2020, also in Bergen. The purpose of the seminar was to raise awareness about fish ethics together with severity classification and humane endpoints in fish studies, using examples from farmed fish, mainly salmonids and lumpfish. The overall aim of the workshop was to better define humane endpoints in fish experiments, as well as to discuss suggestions for development and use of score sheets for assessing clinical signs related to endpoints. Endpoints for fish should not only be based on what we know about fish diseases and the lesions they induce but should also take into consideration knowledge about fish species and life stage, fish anatomy, physiology and the general state and behaviour of the fish. For this reason, to reinforce that endpoints should come from the animal's perspective and needs, we renamed humane endpoints for fish to piscine endpoints. This paper reports the main messages from the workshop sessions including advice on development and use of score sheets.

Hazards of current concentration-setting practices in environmental toxicology studies

The setting of concentrations for testing substances in ecotoxicological studies is often based on fractions of the concentrations that cause 50% mortality (LC50 or LD50) rather than environmentally relevant levels. This practice can result in exposures to animals at test concentrations that are magnitudes of order greater than those experienced in the environment. Often, such unrealistically high concentrations may cause non-specific biochemical or morphologic changes that primarily reflect the near-lethal health condition of the animal subjects, as opposed to effects characteristic of the particular test compound. Meanwhile, it is recognized that for many chemicals, the toxicologic mode of action (MOA) responsible for lethality may differ entirely from the MOAs that cause various sublethal effects. One argument for employing excessively high exposure concentrations in sublethal studies is to ensure the generation of positive toxicological effects, which can then be used to establish safety thresholds; however, it is possible that the pressure to produce exposure-related effects may also contribute to false positive outcomes. The purpose of this paper is to explore issues involving some current usages of acute LC50 data in ecotoxicology testing, and to propose an alternative strategy for performing this type of research moving forward. Toward those ends, a brief literature survey was conducted to gain an appreciation of methods that are currently being used to set test concentrations for sublethal definitive studies.

Evaluation of the fish acute toxicity test for pesticide registration

The U.S. Environmental Protection Agency (USEPA) uses the in vivo fish acute toxicity test to assess potential risk of substances to non-target aquatic vertebrates. The test is typically conducted on a cold and a warm freshwater species and a saltwater species for a conventional pesticide registration, potentially requiring upwards of 200 or more fish. A retrospective data evaluation was conducted to explore the potential for using fewer fish species to support conventional pesticide risk assessments. Lethal concentration 50% (LC50) values and experimental details were extracted and curated from 718 studies on fish acute toxicity submitted to USEPA. The LC50 data were analysed to determine, when possible, the relative sensitivity of the tested species to each pesticide. One of the tested freshwater species was most sensitive in 85% of those cases. The tested cold freshwater species was the most sensitive overall among cases with established relative sensitivity and was within 3X of the LC50 value of the most sensitive species tested in 98% of those cases. The results support potentially using fewer than three fish species to conduct ecological risk assessments for the registration of conventional pesticides.

Ensemble multiclassification model for aquatic toxicity of organic compounds

With environmental pollution becoming increasingly serious, organic compounds have become the main hazard of environmental pollution and exert substantial negative impacts on aquatic organisms. In research pertaining to the acute toxicity of organic compounds, traditional biological experimental methods are time-consuming and expensive. In addition, computer-aided binary classification models cannot accurately classify acute toxicity. Therefore, the multiclassication model is necessary for more accurate classification of acute toxicity. In this study, median lethal concentrations of 373 organic compounds in the environmental toxicology datasets ECOTOX and EAT5 were used. These chemicals were classified into four categories based on the European Economic Community criteria. Then the random forest, support vector machine, extreme gradient boosting, adaptive gradient boosting, and C5.0 decision tree algorithms and eight molecular fingerprints were used to build a multiclassification base model for the acute toxicity of organic compounds. The base models were repeated 100 times with fivefold cross-validation and external validation. The ensemble model was obtained by the voting method. The best base classifier was ExtendFP-C5.0, which had an accuracy, sensitivity and specificity values of 87.30%, 87.32% and 95.76% for external validation, and the voting ensemble model performance of 96.92%, 96.93% and 98.97%, respectively. The ensemble model achieved a higher accuracy than previously reported studies. Our study will help to further classify the acute toxicity of organic compounds to aquatic organisms and predict the hazard classes of organic compounds.

Recapitulation of Retinal Damage in Zebrafish Larvae Infected with Zika Virus

Zebrafish are increasingly being utilized as a model to investigate infectious diseases and to advance the understanding of pathogen-host interactions. Here, we take advantage of the zebrafish to recapitulate congenital ZIKV infection and, for the first time, demonstrate that it can be used to model infection and reinfection and monitor anti-viral and inflammatory immune responses, as well as brain growth and eye abnormalities during embryonic development. By injecting a Brazilian strain of ZIKV into the yolk sac of one-cell stage embryos, we confirmed that, after 72 h, ZIKV successfully infected larvae, and the physical condition of the virus-infected hosts included gross morphological changes in surviving embryos (84%), with a reduction in larval head size and retinal damage characterized by increased thickness of the lens and inner nuclear layer. Changes in locomotor activity and the inability to perceive visual stimuli are a result of changes in retinal morphology caused by ZIKV. Furthermore, we demonstrated the ability of ZIKV to replicate in zebrafish larvae and infect new healthy larvae, impairing their visual and neurological functions. These data reinforce the deleterious activity of ZIKV in the brain and visual structures and establish the zebrafish as a model to study the molecular mechanisms involved in the pathology of the virus.

A Critical Review of the Availability, Reliability, and Ecological Relevance of Arctic Species Toxicity Tests for Use in Environmental Risk Assessment

There is a pressing need to understand the impact of contaminants on Arctic ecosystems; however, most toxicity tests are based on temperate species, and there are issues with reliability and relevance of bioassays in general. Together this may result in an underestimation of harm to Arctic organisms and contribute to significant uncertainty in risk assessments. To help address these concerns, a critical review to assess reported effects for these species, quantify methodological and endpoint relevance gaps, and identify future research needs for testing was performed. We developed uniform criteria to score each study, allowing an objective comparison across experiments to quantify their reliability and relevance. We scored a total of 48 individual studies, capturing 39 tested compounds, 73 unique Arctic test species, and 95 distinct endpoints published from 1975 to 2021. Our analysis shows that of 253 test substance and species combinations scored (i.e., a unique toxicity test), 207 (82%) failed to meet at least one critical study criterion that contributes to data reliability for use in risk assessment. Arctic-focused toxicity testing needs to ensure that exposures can be analytically confirmed, include environmentally realistic exposure scenarios, and report test methods more thoroughly. Significant data gaps were identified as related to standardized toxicity testing with Arctic species, diversity of compounds tested with these organisms, and the inclusion of ecologically relevant sublethal and chronic endpoints assessed in Arctic toxicity testing. Overall, there needs to be ongoing improvement in test conduction and reporting in the scientific literature to support effective risk assessments in an Arctic context. Environ Toxicol Chem 2022;41:46-72. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Zebrafish Beyond the Bench: The 'Plataforma Zebrafish Open Doors' Programme

The Butantan Institute is a pioneering Brazilian health sciences institution, which also houses a large science park with museums that contribute to ongoing science education for schools and the wider community. In recent years, as part of Butantan Institute's Plataforma Zebrafish™, zebrafish embryos have been used for the dissemination of scientific knowledge during on-site events and as part of outreach campaigns to non-scientific audiences, mostly children. The aim of this work is mainly to demystify the activities of the scientific researcher, highlight the role of science in the furthering of knowledge, and increase public interest and confidence in science. In this article, the Institute's 'Plataforma Zebrafish Open Doors' programme is described, which offered guided tours of the laboratory facilities. The tours gave visitors the opportunity to observe zebrafish research and embryo development, and to use the knowledge gained from this experience as a framework for understanding fundamental ethical issues. During the 2-day event, around 800 visitors (most of them school-age children) attended. Together with the guided tours, our experience of outreach offered meaningful opportunities to bring children and members of the public closer to science and 'real-life' scientists, hopefully inspiring and encouraging the next generation of scientists. It also gave the scientists an opportunity to engage more closely with wider society. We believe that these activities also substantially contribute to the wider dissemination of relevant experimental results that have been obtained with public funding and that impact society in general.

Dying for change: A roadmap to refine the fish acute toxicity test after 40 years of applying a lethal endpoint

The fish acute toxicity test (TG203; OECD, 2019) is frequently used and highly embedded in hazard and risk assessment globally. The test estimates the concentration of a chemical that kills 50% of the fish (LC₅₀) over a 96 h exposure and is considered one of the most severe scientific procedures undertaken. Over the years, discussions at the Organisation for Economic Co-operation and Development (OECD) have resulted in changes to the test which reduce the number of fish used, as well as the development of a (potential) replacement test (TG236, OECD, 2013). However, refinement of the mortality endpoint with an earlier (moribundity) endpoint was not considered feasible during the Test Guideline's (TG) last update in 2019. Several stakeholders met at a UK-based workshop to discuss how TG203 can be refined, and identified two key opportunities to reduce fish suffering: (1) application of clinical signs that predict mortality and (2) shortening the test duration. However, several aspects need to be addressed before these refinements can be adopted. TG203 has required recording of major categories of sublethal clinical signs since its conception, with the option to record more detailed signs introduced in the 2019 update. However, in the absence of guidance, differences in identification, recording and reporting of clinical signs between technicians and laboratories is likely to have generated piecemeal data of varying quality. Harmonisation of reporting templates, and training in clinical sign recognition and recording are needed to standardise clinical sign data. This is critical to enable robust data-driven detection of clinical signs that predict mortality. Discussions suggested that the 96 h duration of TG203 cannot stand up to scientific scrutiny. Feedback and data from UK contract research organisations (CROs) conducting the test were that a substantial proportion of mortalities occur in the first 24 h. Refinement of TG203 by shortening the test duration would reduce suffering (and test failure rate) but requires a mechanism to correct new results to previous 96 h LC₅₀ data. The actions needed to implement both refinement opportunities are summarised here within a roadmap. A shift in regulatory assessment, where the 96 h LC₅₀ is a familiar base for decisions, will also be critical.

A Method to Screen for Consistency of Effect in Laboratory Toxicity Tests: A Case Study with Anurans and the Herbicide Atrazine

This paper presents a semiquantitative method to help ecotoxicologists evaluate the consistency of data within the available peer-reviewed literature. In this case study, we queried whether there is consistent evidence of direct toxicity in Anurans exposed to atrazine at concentrations ≤ 100 μg/L under laboratory conditions. Atrazine was selected because of the relatively large repository of Anuran toxicity data. To accomplish this, we interrogated available data found in recent quantitative weight-of-evidence risk assessments for atrazine with a series of yes or no questions developed a priori. The questions examined consistency of reported effects within and between studies, within and between species, and across a wide range of endpoints categories (e.g., survivorship, growth and development, reproduction). The analysis found no compelling evidence of a consistent direct effect in Anurans around growth and development, reproduction, or survivorship at concentrations of up to at least 100 μg/L atrazine in laboratory studies. Further work is needed to refine the approach, including accounting for the magnitude of the reported effects. However, we recommend that ecotoxicologists employ some method of formal consistency of effects assessment method routinely before performing toxicity tests, in the contextualizing of new data, and in reviews of contaminants.

Development of an Enhanced Mechanistically Driven Mode of Action Classification Scheme for Adverse Effects on Environmental Species

This study developed a novel classification scheme to assign chemicals to a verifiable mechanism of (eco-)toxicological action to allow for grouping, read-across, and in silico model generation. The new classification scheme unifies and extends existing schemes and has, at its heart, direct reference to molecular initiating events (MIEs) promoting adverse outcomes. The scheme is based on three broad domains of toxic action representing nonspecific toxicity (e.g., narcosis), reactive mechanisms (e.g., electrophilicity and free radical action), and specific mechanisms (e.g., associated with enzyme inhibition). The scheme is organized at three further levels of detail beyond broad domains to separate out the mechanistic group, specific mechanism, and the MIEs responsible. The novelty of this approach comes from the reference to taxonomic diversity within the classification, transparency, quality of supporting evidence relating to MIEs, and that it can be updated readily.

Development of In Vitro Corneal Models: Opportunity for Pharmacological Testing

The human eye is a specialized organ with a complex anatomy and physiology, because it is characterized by different cell types with specific physiological functions. Given the complexity of the eye, ocular tissues are finely organized and orchestrated. In the last few years, many in vitro models have been developed in order to meet the 3Rs principle (Replacement, Reduction and Refinement) for eye toxicity testing. This procedure is highly necessary to ensure that the risks associated with ophthalmic products meet appropriate safety criteria. In vitro preclinical testing is now a well-established practice of significant importance for evaluating the efficacy and safety of cosmetic, pharmaceutical, and nutraceutical products. Along with in vitro testing, also computational procedures, herein described, for evaluating the pharmacological profile of potential ocular drug candidates including their toxicity, are in rapid expansion. In this review, the ocular cell types and functionality are described, providing an overview about the scientific challenge for the development of three-dimensional (3D) in vitro models.