Baseline characteristics and statistical implications for the OECD 210 fish early-life stage chronic toxicity test

Realistic nitrate concentrations diminish reproductive indicators in Skiffia lermae, an endemic species in critical endangered status

Goodeinae is a subfamily of critically endangered fish native to central Mexico. Populations of Skiffia lermae, a species belonging to this subfamily, have significantly decreased in the past two decades. A previous study showed that S. lermae is sensitive to acute nitrate-nitrogen (NO3-N) exposure, leading to noticeable changes in both behavioral and histopathological bioindicators. The aim herein was to determine the vulnerability of S. lermae to NO3-N exposure at realistic concentrations registered in freshwater ecosystems in central Mexico where the species was historically reported. Offspring of S. lermae were chronically exposed during 60 days to concentrations of 5, 10 and 20 mg NO3-N/L, with 2 mg NO3-N/L used as the reference value (control). Survival rate, feeding behavior, aquatic surface respiration, body growth, scaled mass index, immature red blood cells, as well as histopathological changes in branchial, hepatic and gonadal tissues were evaluated. Additionally, this study analyzed water quality in freshwater ecosystems where S. lermae presently persists. The results showed decreased survival as NO3-N concentration increased, as well as increased feeding latency, aquatic surface respiration and histological damage in the gills and liver. These organs showed differential sex-dependent responses to NO3-N exposure; females were more sensitive than males. In the ovaries, a decreased density of stage III oocytes was associated with increased NO3-N concentrations. No changes were observed in body growth and number of immature red blood cells. Concentrations recorded in the three freshwater ecosystems that S. lermae inhabit were below 2 mg NO3-N/L. Together, the results could explain why the species has disappeared from more contaminated freshwater ecosystems where NO3-N levels exceed 5 mg/L. Moreover, the study warns about the risks of increasing NO3-N concentrations in the current sites where the species lives.

Toxicity of ciprofloxacin and ofloxacin to Moina macrocopa and investigation of p-value adjustments for (eco)toxicological studies

Ciprofloxacin (CFX) and ofloxacin (OFX) are commonly found as residual contaminants in aquatic environments, posing potential risks to various species. To ensure the safety of aquatic wildlife, it is essential to determine the toxicity of these antibiotics and establish appropriate concentration limits. Additionally, in (eco)toxicological studies, addressing the issue of multiple hypothesis testing through p-value adjustments is crucial for robust decision-making. In this study, we assessed the no observed adverse effect concentration (NOAEC) of CFX and OFX on Moina macrocopa across a concentration range of 0-400 µg L-1. Furthermore, we investigated multiple p-value adjustments to determine the NOAECs. Our analysis yielded consistent results across seven different p-value adjustments, indicating NOAECs of 100 µg CFX L-1 for age at first reproduction and 200 µg CFX L-1 for fertility. For OFX treatment, a NOAEC of 400 µg L-1 was observed for both biomarkers. However, further investigation is required to establish the NOAEC of OFX at higher concentrations with greater certainty. Our findings demonstrate that CFX exhibits higher toxicity compared to OFX, consistent with previous research. Moreover, this study highlights the differential performance of p-value adjustment methods in terms of maintaining statistical power while controlling the multiplicity problem, and their practical applicability. The study emphasizes the low NOAECs for these antibiotics in the zooplanktonic group, highlighting their significant risks to ecological and environmental safety. Additionally, our investigation of p-value adjustment approaches contributes to a deeper understanding of their performance characteristics, enabling (eco)toxicologists to select appropriate methods based on their specific needs and priorities.

Exploring Alternatives for Marine Toxicity Testing: Initial Evaluation of Fish Embryo and Mysid Tests

Current regulations require that toxicity assessments be performed using standardized toxicity testing methods, often using fish. Recent legislation in both the European Union and United States has mandated that toxicity testing alternatives implement the 3Rs of animal research (replacement, reduction, and refinement) whenever possible. There have been advances in the development of alternatives for freshwater assessments, but there is a lack of analogous developments for marine assessments. One potential alternative testing method is the fish embryo toxicity (FET) test, which uses fish embryos rather than older fish. In the present study, FET methods were applied to two marine model organisms, the sheepshead minnow and the inland silverside. Another potential alternative is the mysid shrimp survival and growth test, which uses an invertebrate model. The primary objective of the present study was to compare the sensitivity of these three potential alternative testing methods to two standardized fish-based tests using 3,4-dichloroaniline (DCA), a common reference toxicant. A secondary objective was to characterize the ontogeny of sheepshead minnows and inland silversides. This provided a temporal and visual guide that can be used to identify appropriately staged embryos for inclusion in FET tests and delineate key developmental events (e.g., somite development, eyespot formation, etc.). Comparison of the testing strategies for assessing DCA indicated that: (1) the standardized fish tests possessed comparable sensitivity to each other; (2) the mysid shrimp tests possessed comparable sensitivity to the standardized fish tests; (3) the sheepshead minnow and inland silverside FET tests were the least sensitive testing strategies employed; and (4) inclusion of sublethal endpoints (i.e., hatchability and pericardial edema) in the marine FETs increased their sensitivity. Environ Toxicol Chem 2024;43:1285-1299. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Occurrence and implications of per and polyfluoroalkyl substances in animal feeds used in laboratory toxicity testing

The exceptional thermal and chemical stability and the amphiphilicity of per- and polyfluoroalkyl substances (PFAS) have resulted in widespread use and subsequent contamination in environmental media and biota. Concerns surrounding toxicity have led to numerous animal-based toxicity studies. Due to the ubiquity of PFAS and the low parts per trillion (ppt) health advisory levels for drinking water, several contamination elimination protocols have been implemented. In addition, it is urgently necessary to perform low-dose experiments, but due to unknown pathways for entry of unwanted PFAS, low-dose studies are extremely challenging to conduct. However, animal feed sources are a likely route that could introduce unwanted PFAS into experiments, yet investigations of PFAS in common animal feeds are lacking. Here, we report the examination of PFAS levels in eighteen different animal feeds, representing a range of diets fed to diverse taxa. We evaluated whether PFAS levels in feeds were correlated with ingredient composition (plant versus animal-based) or dietary habits of lab animals (amphibian, fish, invertebrate, mammal). PFOS, PFHxS, PFOA, and short-chain perfluoroalkyl carboxylic acids had the highest detection levels and frequencies across all samples. Different food ingredients led to different PFAS profiles. No meaningful levels of PFAS precursors were detected. We demonstrate that PFAS contamination in animal feed is pervasive. Reducing food-sourced PFAS is a critical, albeit challenging task to improve interpretability of in vivo exposures.

Chemical hazard of robotic hull in-water cleaning discharge on coastal embryonic fish

In-water cleaning (IWC) involves the removal of biofilms and foulants from the hull of a ship using brush or water jet. During IWC, several factors associated with the harmful chemical contaminants release to the marine environment, which can create "hotspots" of chemical contamination in coastal areas. To elucidate the potential toxic effects of IWC discharge, we investigated developmental toxicity in embryonic flounder, which are sensitive life stage to chemical exposure. Zinc and copper were the dominant metals, while zinc pyrithione was the most abundant biocide associated with IWC discharge in two remotely operated IWC. Discharge from IWC carried by both remotely operated vehicles (ROVs) produced developmental malformations including pericardial edema, spinal curvature, and tail-fin defects. In an analyses of differential gene expression profiles (fold-change of genes with a cutoff < 0.05) as assessed by high-throughput RNA sequencing, genes associated with muscle development were commonly and significantly changed. The gene ontology (GO) of embryos exposed to IWC discharge from ROV A activities highly enriched muscle and heart development, while cell signaling and transport were evident in embryos exposed to IWC discharge of ROV B. We analyzed the gene network by significant GO terms. In the network, TTN, MYOM1, CASP3, and CDH2 genes appeared to be key regulators of the toxic effects on muscle development. In embryos exposed to ROV B discharge, HSPG2, VEGFA, and TNF genes related to the nervous system pathway were affected. These results shed light on the potential impacts of muscle and nervous system development in non-target coastal organisms exposed to contaminants found in IWC discharge.

Adapting classic paradigms to analyze alterations of shoal-wide behavior in early-life stages of zebrafish (Danio rerio) - A case study with fluoxetine

Given the strong increase in prescription of neuroactive pharmaceuticals, neurotoxicity has received growing concern in science and the public. Regulatory requirements stimulated the development of new methods to evaluate the risk of neurotoxic substances for humans and the environment, and, with respect to potential damage to aquatic ecosystems, a variety of behavior-based assays have been proposed for neurotoxicity testing, most of which, however, are restricted to changes in the behavior of individual fish. Since many fish species form shoals under natural conditions, this may cause important aspects of behavior to be overlooked and there is a need for behavior assays integrating individual behavior with behavior of the entire swarm. In order to combine more environmentally realistic sub-chronic exposure scenarios with undistorted social behavior and animal welfare considerations, two behavioral assays are proposed that might be integrated into early-life stage toxicity studies according to OECD TG 210, which are commonly run for a multitude of regulations: To this end, protocols for a novel tank test and a predator response assay were adapted to also record the behavior of free-swimming zebrafish (Danio rerio) juveniles within shoals. Comparisons of the diving response (novel tank) or the shoal's coherence and position relative to the stimulus (predator) with control groups allow conclusions about the anxiety state of the fish, which might well have an impact on survival chances in the wild. As a model substance, the antidepressant fluoxetine ((RS)-N-Methyl-3-phenyl-3-(4-trifluoromethylphenoxy)propylamine) produced adverse effects down to concentrations three orders of magnitude below the EC₁₀ from acute fish embryo toxicity tests according to OECD TG 236. With the integration of such behavior tests into OECD TG 210, important population-relevant information on potential neurotoxicity can be collected without increasing the number of experimental animals.

The potential ecological risk of veterinary pharmaceuticals from swine wastewater on freshwater aquatic environment

The impact of pharmaceutical residue transport in the aquatic ecosystem has become an increasing subject of environmental interest due to the inherent bioactivity of trace levels of antibiotics and the negative environmental and public health impact. In this study, three veterinary pharmaceuticals including tetracycline, ivermectin, and salicylic acid were investigated in a piggery effluent from Western Cape, South Africa. Three freshwater organisms' taxonomic groups (Pseudokirchneriella subcapitata, Daphnia magna, and Tetrahymena thermophila) were used to determine the ecological risk of different treated piggery effluent concentration range of 1%, 10%, and 20% and a cocktail mixture of veterinary pharmaceuticals of environmental concerns. The average concentration of veterinary pharmaceuticals was in the range of 47.35, 7.19, and 1.46 μg L^-1 for salicylic acid, chloro-tetracycline, and ivermectin, respectively. P. subcapitata exposed to 20% piggery wastewater effluent at 24- and 48-h EC₅₀ showed a toxicity value of 14.2% and 13.6% (v/v), respectively. The study established the ecological risk of the test compounds as low to medium risk for low-level dose and low concentrations of piggery effluent. The relative sensitivity ranking of the taxa drawn is microalgae > protozoa > Cladocera. The study results demonstrated that a high dose of piggery effluent and mixtures of veterinary pharmaceutical can pose a high risk in freshwater ecosystems. PRACTITIONER POINTS: Transport processes of veterinary antibiotics into the environment were investigated. Dilution effect of the veterinary pharmaceutical on the antibiotic levels exists. High dose of piggery effluent presented an ecological risk.

Investigating endocrine-disrupting properties of chemicals in fish and amphibians: Opportunities to apply the 3Rs

Many regulations are beginning to explicitly require investigation of a chemical's endocrine-disrupting properties as a part of the safety assessment process for substances already on or about to be placed on the market. Different jurisdictions are applying distinct approaches. However, all share a common theme requiring testing for endocrine activity and adverse effects, typically involving in vitro and in vivo assays on selected endocrine pathways. For ecotoxicological evaluation, in vivo assays can be performed across various animal species, including mammals, amphibians, and fish. Results indicating activity (i.e., that a test substance may interact with the endocrine system) from in vivo screens usually trigger further higher-tier in vivo assays. Higher-tier assays provide data on adverse effects on relevant endpoints over more extensive parts of the organism's life cycle. Both in vivo screening and higher-tier assays are animal- and resource-intensive and can be technically challenging to conduct. Testing large numbers of chemicals will inevitably result in the use of large numbers of animals, contradicting stipulations set out within many regulatory frameworks that animal studies be conducted as a last resort. Improved strategies are urgently required. In February 2020, the UK's National Centre for the 3Rs and the Health and Environmental Sciences Institute hosted a workshop ("Investigating Endocrine Disrupting Properties in Fish and Amphibians: Opportunities to Apply the 3Rs"). Over 50 delegates attended from North America and Europe, across academia, laboratories, and consultancies, regulatory agencies, and industry. Challenges and opportunities in applying refinement and reduction approaches within the current animal test guidelines were discussed, and utilization of replacement and/or new approach methodologies, including in silico, in vitro, and embryo models, was explored. Efforts and activities needed to enable application of 3Rs approaches in practice were also identified. This article provides an overview of the workshop discussions and sets priority areas for follow-up. Integr Environ Assess Manag 2022;18:442-458. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Is hull cleaning wastewater a potential source of developmental toxicity on coastal non-target organisms?

Chemical contaminants can be discharged by vessel hull cleaning processes, such as scraping, jet spraying, and painting, all of which produce readily transportable contaminants into the marine environment, where they are referred to as 'hotspots' of contamination in coastal areas. However, many countries have not yet established effective evaluation methods for disposal of waste mixtures or management guidelines for areas of hull cleaning. To define the toxic effects of wastewater from vessel hull cleaning in dry docks on resident non-target organisms, we investigated the chemical concentrations and developmental toxicity on embryonic flounder, which is an organism sensitive to chemical contamination. In this study, the dominant inorganic metal discharged was zinc when cleaning Ship A (300 tons) and copper for Ship B (5,000 tons). The wastewater from high-pressure water blasting (WHPB) of Ship A (300 tons) and Ship B (5,000 tons) produced a largely overlapping suite of developmental malformations including pericardial edema, spinal curvature, and tail fin defects. Forty-eight hours after exposure, the frequency percentage of malformation began to increase in embryos exposed to a 500-fold dilution of WHPB from Ships A and B. We performed transcriptome sequencing to characterize the toxicological developmental effects of WHPB exposure at the molecular level. The results of the analysis revealed significantly altered expression of genes associated with muscle cell differentiation, actin-mediated cell contraction, and nervous system development (cutoff P < 0.01) in embryonic flounder exposed to high-pressure cleaning effluent from Ship A. Genes associated with chromatin remodeling, cell cycling, and insulin receptor signaling pathways were significantly altered in embryonic flounder exposed to WHPB of Ship B (cutoff P < 0.01). These findings provide a greater understanding of the developmental toxicity and potential effects of WHPB effluent on coastal embryonic fish. Furthermore, our results could inform WHPB effluent management practices to reduce impacts on non-target coastal organisms.

Comparative Assessment of the Sensitivity of Fish Early-Life Stage, Daphnia, and Algae Tests to the Chronic Ecotoxicity of Xenobiotics: Perspectives for Alternatives to Animal Testing

No-observed-effect concentrations (NOECs) are used in environmental hazard classification and labeling of chemicals and their environmental risk assessment. They are typically obtained using standard tests such as the fish early-life stage (FELS) toxicity test, the chronic Daphnia reproduction test, and the algae growth inhibition test. Given the demand to replace and reduce animal tests, we explored the impact of the FELS toxicity test on the determination of effect concentrations by comparing the FELS toxicity test and the Daphnia and algae acute or chronic toxicity tests. Lowest-observed-effect concentrations (LOECs) were used instead of NOECs for better comparison with median lethal or effect concentration data. A database of FELS toxicity data for 223 compounds was established. Corresponding Daphnia and algae toxicity tests were identified using established databases (US Environmental Protection Agency ECOTOX, Organisation for Economic Co-operation and Development QSAR Toolbox, eChemPortal, EnviroTox, and OpenFoodTox). Approximately 9.5% of the investigated compounds showed a 10-fold higher sensitivity with the FELS toxicity test in comparison with the lowest effect concentrations obtained with any of the other tests. Some of these compounds have been known or considered as endocrine disrupting, or are other non-narcotic chemicals, indicating that the higher sensitivity in the FELS toxicity test is related to a specific mechanism of action. Targeting these mechanisms by alternative test systems or endpoints, using fish embryos for instance, may allow reduction or replacement of the FELS toxicity test or may allow us to prioritize compounds for conduction of the FELS toxicity test. Environ Toxicol Chem 2019;39:30-41. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Historical control data for the interpretation of ecotoxicity data: are we missing a trick?

Wildlife can be exposed to chemicals in the environment from various anthropogenic sources. Ecotoxicity studies, undertaken to address the risks from potential exposure to chemicals, vary in their design e.g. duration of exposure, effect types and endpoints measured. Ecotoxicity studies measure biological responses to test item exposure. Responses can be highly variable, with limited opportunity for control of extrinsic sources of variability. It is critical to distinguish between treatment-related effects and background 'normal variability' when interpreting results. Historical control data (HCD) can be a valuable tool in contextualising results from single studies against previous studies performed under similar conditions. This paper discusses the case for better use of HCD in ecotoxicology assessments, illustrating with case studies the value and difficulties of using HCD in interpretation of results of standard and higher-tier study designs. HCD are routinely used in mammalian toxicology for human health assessments, but not directly in ecotoxicology. The possible reasons for this are discussed e.g., different data types, the potential to mask effects, and the lack of guidance. These concerns are real but not insurmountable and we would like to see organisations such as OECD, EFSA and USEPA develop guidance on the principles of HCD collection. Hopefully, this would lead to greater use of HCD and regulatory acceptance. We believe this is not only a scientifically valid approach but also an ethical issue that is in line with societally driven legal mandates to minimise the use of vertebrate testing in chemical regulatory decision making.

SSDs revisited: part II-practical considerations in the development and use of application factors applied to species sensitivity distributions

Application factors are routinely applied in the extrapolation of laboratory aquatic toxicity data to ensure protection from exposure to chemicals in the natural environment. The magnitude of the application factor is both a scientific and a policy decision, but in any case, it should be rooted in scientific knowledge so as to not be arbitrary. Information-rich chemicals are often subjected to species sensitivity distribution (SSD) analysis to transparently describe certain aspects of assessment uncertainty and are normally subjected to much smaller application factors than screening information data sets. We describe a new set of tools useful to assess the quality of SSDs. Twenty-two data sets and 19 chemicals representing agrochemicals, biocides, surfactants, metals, and common wastewater contaminants were compiled to demonstrate how the tools can be used. "Add-one-in" and "leave-one-out" simulations were used to investigate SSD robustness and develop quantitative evidence for the use of application factors. Theoretical new toxicity data were identified for add-one-in simulations based on the expected probabilities necessary to lower the hazardous concentration to 5% of a species (HC5) by a factor of 2, 3, 5, or 10. Simulations demonstrate the basis for application factors in the range of 1 to 5 for well-studied chemicals with high-quality SSDs. Leave-one-out simulations identify the fact that the most influential values in the SSD come from the extremes of the sensitive and tolerant toxicity values. Mesocosm and field data consistently demonstrate that HC5s are conservative, further justifying the use of small application factors for high-quality SSDs. Environ Toxicol Chem 2019;38:1526-1541. © 2019 SETAC.

Species sensitivity distributions for use in environmental protection, assessment, and management of aquatic ecosystems for 12 386 chemicals

The present study considers the collection and use of ecotoxicity data for risk assessment with species sensitivity distributions (SSDs) of chemical pollution in surface water, which are used to quantify the likelihood that critical effect levels are exceeded. This fits the European Water Framework Directive, which suggests using models to assess the likelihood that chemicals affect water quality for management prioritization. We derived SSDs based on chronic and acute ecotoxicity test data for 12 386 compounds. The log-normal SSDs are characterized by the median and the standard deviation of log-transformed ecotoxicity data and by a quality score. A case study illustrates the utility of SSDs for water quality assessment and management prioritization. We quantified the chronic and acute mixture toxic pressure of mixture exposures for >22 000 water bodies in Europe for 1760 chemicals for which we had both exposure and hazard data. The results show the likelihood of mixture exposures exceeding a negligible effect level and increasing species loss. The SSDs in the present study represent a versatile and comprehensive approach to prevent, assess, and manage chemical pollution problems. Environ Toxicol Chem 2019;38:905-917. © 2019 SETAC.

Enhancing the fathead minnow fish embryo toxicity test: Optimizing embryo production and assessing the utility of additional test endpoints

The fathead minnow fish embryo toxicity (FET) test has been identified as a potential alternative to toxicity test methods that utilize older fish. However, several challenges have been identified with the fathead minnow FET test, including: 1) difficulties in obtaining appropriately-staged embryos for FET test initiation, 2) a paucity of data comparing fathead minnow FET test performance to the fathead minnow larval growth and survival (LGS) test and 3) a lack of sublethal endpoints that could be used to estimate chronic toxicity and/or predict adverse effects. These challenges were addressed through three study objectives. The first objective was to optimize embryo production by assessing the effect of breeding group composition (number of males and females) on egg production. Results showed that groups containing one male and four females produced the largest clutches, enhancing the likelihood of procuring sufficient numbers of embryos for FET test initiation. The second study objective was to compare the performance of the FET test to that of the fathead minnow LGS test using three reference toxicants. The FET and LGS tests were similar in their ability to predict the acute toxicity of sodium chloride and ethanol, but the FET test was found to be more sensitive than the LGS test for sodium dodecyl sulfate. The last objective of the study was to evaluate the utility and practicality of several sublethal metrics (i.e., growth, developmental abnormalities and growth- and stress-related gene expression) as FET test endpoints. Developmental abnormalities, including pericardial edema and hatch success, were found to offer the most promise as additional FET test endpoints, given their responsiveness, potential for predicting adverse effects, ease of assessment and low cost of measurement.

Meta-analysis of fish early life stage tests-Association of toxic ratios and acute-to-chronic ratios with modes of action

Fish early life stage (ELS) tests (Organisation for Economic Co-operation and Development test guideline 210) are widely conducted to estimate chronic fish toxicity. In these tests, fish are exposed from the embryonic to the juvenile life stages. To analyze whether certain modes of action are related to high toxic ratios (i.e., ratios between baseline toxicity and experimental effect) and/or acute-to-chronic ratios (ACRs) in the fish ELS test, effect concentrations (ECs) for 183 compounds were extracted from the US Environmental Protection Agency's ecotoxicity database. Analysis of ECs of narcotic compounds indicated that baseline toxicity could be observed in the fish ELS test at similar concentrations as in the acute fish toxicity test. All nonnarcotic modes of action were associated with higher toxic ratios, with median values ranging from 4 to 9.3 × 10⁴ (uncoupling < reactivity < neuromuscular toxicity < methemoglobin formation < endocrine disruption < extracellular matrix formation inhibition). Four modes of action were also found to be associated with high ACRs: 1) lysyl oxidase inhibition leading to notochord distortion, 2) putative methemoglobin formation or hemolytic anemia, 3) endocrine disruption, and 4) compounds with neuromuscular toxicity. For the prediction of ECs in the fish ELS test with alternative test systems, endpoints targeted to the modes of action of compounds with enhanced toxic ratios or ACRs could be used to trigger fish ELS tests or even replace these tests. Environ Toxicol Chem 2018;37:955-969. © 2018 SETAC.

Alternative approaches to vertebrate ecotoxicity tests in the 21st century: A review of developments over the last 2 decades and current status

The need for alternative approaches to the use of vertebrate animals for hazard assessment of chemicals and pollutants has become of increasing importance. It is now the first consideration when initiating a vertebrate ecotoxicity test, to ensure that unnecessary use of vertebrate organisms is minimized wherever possible. For some regulatory purposes, the use of vertebrate organisms for environmental risk assessments has been banned; in other situations, the number of organisms tested has been dramatically reduced or the severity of the procedure refined. However, there is still a long way to go to achieve a complete replacement of vertebrate organisms to generate environmental hazard data. The development of animal alternatives is based not just on ethical considerations but also on reducing the cost of performing vertebrate ecotoxicity tests and in some cases on providing better information aimed at improving environmental risk assessments. The present Focus article provides an overview of the considerable advances that have been made toward alternative approaches for ecotoxicity assessments over the last few decades. Environ Toxicol Chem 2016;35:2637-2646. © 2016 SETAC.

Regulatory ecotoxicity testing of nanomaterials - proposed modifications of OECD test guidelines based on laboratory experience with silver and titanium dioxide nanoparticles

Regulatory ecotoxicity testing of chemicals is of societal importance and a large effort is undertaken at the OECD to ensure that OECD test guidelines (TGs) for nanomaterials (NMs) are available. Significant progress to support the adaptation of selected TGs to NMs was achieved in the context of the project MARINA ( http://www.marina-fp7.eu/ ) funded within the 7th European Framework Program. Eight OECD TGs were adapted based on the testing of at least one ion-releasing NM (Ag) and two inert NMs (TiO₂). With the materials applied, two main variants of NMs (ion releasing vs. inert NMs) were addressed. As the modifications of the test guidelines refer to general test topics (e.g. test duration or measuring principle), we assume that the described approaches and modifications will be suitable for the testing of further NMs with other chemical compositions. Firm proposals for modification of protocols with scientific justification(s) are presented for the following tests: growth inhibition using the green algae Raphidocelis subcapitata (formerly: Pseudokirchneriella subcapitata; TG 201), acute toxicity with the crustacean Daphnia magna (TG 202), development toxicity with the fish Danio rerio (TG 210), reproduction of the sediment-living worm Lumbriculus variegatus (TG 225), activity of soil microflora (TGs 216, 217), and reproduction of the invertebrates (Enchytraeus crypticus, Eisenia fetida, TGs 220, 222). Additionally, test descriptions for two further test systems (root elongation of plants in hydroponic culture; test on fish cells) are presented. Ecotoxicological data obtained with the modified test guidelines for TiO₂ NMs and Ag NM and detailed method descriptions are available.

Advancing the 3Rs in regulatory ecotoxicology: A pragmatic cross-sector approach

The ecotoxicity testing of chemicals for prospective environmental safety assessment is an area in which a high number of vertebrates are used across a variety of industry sectors. Refining, reducing, and replacing the use of animals such as fish, birds, and amphibians for this purpose addresses the ethical concerns and the increasing legislative requirements to consider alternative test methods. Members of the UK-based National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs) Ecotoxicology Working Group, consisting of representatives from academia, government organizations, and industry, have worked together over the past 6 y to provide evidence bases to support and advance the application of the 3Rs in regulatory ecotoxicity testing. The group recently held a workshop to identify the areas of testing, demands, and drivers that will have an impact on the future of animal use in regulatory ecotoxicology. As a result of these discussions, we have developed a pragmatic approach to prioritize and realistically address key opportunity areas, to enable progress toward the vision of a reduced reliance on the use of animals in this area of testing. This paper summarizes the findings of this exercise and proposes a pragmatic strategy toward our key long-term goals-the incorporation of reliable alternatives to whole-organism testing into regulations and guidance, and a culture shift toward reduced reliance on vertebrate toxicity testing in routine environmental safety assessment. Integr Environ Assess Manag 2016;12:417-421. © 2015 SETAC.

A critical evaluation of the fish early-life stage toxicity test for engineered nanomaterials: experimental modifications and recommendations

There are concerns that regulatory toxicity tests are not fit for purpose for engineered nanomaterials (ENMs) or need modifications. The aim of the current study was to evaluate the OECD 210 fish, early-life stage toxicity test for use with TiO2 ENMs, Ag ENMs, and MWCNT. Both TiO2 ENMS (≤160 mg l(-1)) and MWCNT (≤10 mg l(-1)) showed limited acute toxicity, whilst Ag ENMs were acutely toxic to zebrafish, though less so than AgNO3 (6-day LC50 values of 58.6 and 5.0 µg l(-1), respectively). Evidence of delayed hatching, decreased body length and increased muscle width in the tail was seen in fish exposed to Ag ENMs. Oedema (swollen yolk sacs) was also seen in fish from both Ag treatments with, for example, mean yolk sac volumes of 17, 35 and 39 µm(3) for the control, 100 µg l(-1) Ag ENMs and 5 µg l(-1) AgNO3 treatments, respectively. Among the problems with the standard test guidelines was the inability to maintain the test solutions within ±20 % of nominal concentrations. Pronounced settling of the ENMs in some beakers also made it clear the fish were not being exposed to nominal concentrations. To overcome this, the exposure apparatus was modified with the addition of an exposure chamber that ensured mixing without damaging the delicate embryos/larvae. This allowed more homogeneous ENM exposures, signified by improved measured concentrations in the beakers (up to 85.7 and 88.1 % of the nominal concentrations from 10 mg l(-1) TiO2 and 50 µg l(-1) Ag ENM exposures, respectively) and reduced variance between measurements compared to the original method. The recommendations include: that the test is conducted using exposure chambers, the use of quantitative measurements for assessing hatching and morphometrics, and where there is increased sensitivity of larvae over embryos to conduct a shorter, larvae-only toxicity test with the ENMs.

Development of a total dissolved solids (TDS) chronic effects benchmark for a northern Canadian lake

Laboratory chronic toxicity tests with plankton, benthos, and fish early life stages were conducted with total dissolved solids (TDS) at an ionic composition specific to Snap Lake (Northwest Territories, Canada), which receives treated effluent from the Snap Lake Diamond Mine. Snap Lake TDS composition has remained consistent from 2007 to 2014 and is expected to remain unchanged through the life of the mine: Cl (45%-47%), Ca (20%-21%), Na (10%-11%), sulfate (9%); carbonate (5%-7%), nitrate (4%), Mg (2%-3%), and minor contributions from K and fluoride. The TDS concentrations that resulted in negligible effects (i.e., 10% or 20% effect concentrations) to taxa representative of resident biota ranged from greater than 1100 to greater than 2200 mg/L, with the exception of a 21% effect concentration of 990 mg/L for 1 of 2 early life stage fish dry fertilization tests (wet fertilization results were >1480 mg/L). A conservative, site-specific, chronic effects benchmark for Snap Lake TDS of 1000 mg/L was derived, below the lowest negligible effect concentration for the most sensitive resident taxon tested, the cladoceran, Daphnia magna (>1100 mg/L). Cladocerans typically only constitute a few percent of the zooplankton community and biomass in Snap Lake; other plankton effect concentrations ranged from greater than 1330 to greater than 1510 mg/L. Chironomids, representative of the lake benthos, were not affected by greater than 1380 mg/L TDS. Early life stage tests with 3 fish species resulted in 10% to 20% effect concentrations ranging from greater than 1410 to greater than 2200 mg/L. The testing undertaken is generally applicable to northern freshwaters, and the concept can readily be adapted to other freshwaters either for TDS where ionic composition does not change or for major ionic components, where TDS composition does change.

Impaired anterior swim bladder inflation following exposure to the thyroid peroxidase inhibitor 2-mercaptobenzothiazole part I: Fathead minnow

In the present study, a hypothesized adverse outcome pathway linking inhibition of thyroid peroxidase (TPO) activity to impaired swim bladder inflation was investigated in two experiments in which fathead minnows (Pimephales promelas) were exposed to 2-mercaptobenzothiazole (MBT). Continuous exposure to 1mg MBT/L for up to 22 days had no effect on inflation of the posterior chamber of the swim bladder, which typically inflates around 6 days post fertilization (dpf), a period during which maternally-derived thyroid hormone is presumed to be present. In contrast, inflation of the anterior swim bladder, which occurs around 14dpf, was impacted. Specifically, at 14dpf, approximately 50% of fish exposed to 1mg MBT/L did not have an inflated anterior swim bladder. In fish exposed to MBT through 21 or 22dpf, the anterior swim bladder was able to inflate, but the ratio of the anterior/posterior chamber length was significantly reduced compared to controls. Both abundance of thyroid peroxidase mRNA and thyroid follicle histology suggest that fathead minnows mounted a compensatory response to the presumed inhibition of TPO activity by MBT. Time-course characterization showed that fish exposed to MBT for at least 4 days prior to normal anterior swim bladder inflation had significant reductions in anterior swim bladder size, relative to the posterior chamber, compared to controls. These results, along with similar results observed in zebrafish (see part II, this issue) are consistent with the hypothesis that thyroid hormone signaling plays a significant role in mediating anterior swim bladder inflation and development in cyprinids, and that role can be disrupted by exposure to thyroid hormone synthesis inhibitors. Nonetheless, possible thyroid-independent actions of MBT on anterior swim bladder inflation cannot be ruled out based on the present results. Overall, although anterior swim bladder inflation has not been directly linked to survival as posterior swim bladder inflation has, potential links to adverse ecological outcomes are plausible given involvement of the anterior chamber in sound production and detection.

Early life exposure to PCB126 results in delayed mortality and growth impairment in the zebrafish larvae

The occurrence of chronic or delayed toxicity resulting from the exposure to sublethal chemical concentrations is an increasing concern in environmental risk assessment. The Fish Embryo Toxicity (FET) test with zebrafish provides a reliable prediction of acute toxicity in adult fish, but it cannot yet be applied to predict the occurrence of chronic or delayed toxicity. Identification of sublethal FET endpoints that can assist in predicting the occurrence of chronic or delayed toxicity would be advantageous. The present study characterized the occurrence of delayed toxicity in zebrafish larvae following early exposure to PCB126, previously described to cause delayed effects in the common sole. The first aim was to investigate the occurrence and temporal profiles of delayed toxicity during zebrafish larval development and compare them to those previously described for sole to evaluate the suitability of zebrafish as a model fish species for delayed toxicity assessment. The second aim was to examine the correlation between the sublethal endpoints assessed during embryonal and early larval development and the delayed effects observed during later larval development. After exposure to PCB126 (3-3000ng/L) until 5 days post fertilization (dpf), larvae were reared in clean water until 14 or 28 dpf. Mortality and sublethal morphological and behavioural endpoints were recorded daily, and growth was assessed at 28 dpf. Early life exposure to PCB126 caused delayed mortality (300 ng/L and 3000 ng/L) as well as growth impairment and delayed development (100 ng/L) during the clean water period. Effects on swim bladder inflation and cartilaginous tissues within 5 dpf were the most promising for predicting delayed mortality and sublethal effects, such as decreased standard length, delayed metamorphosis, reduced inflation of swim bladder and column malformations. The EC50 value for swim bladder inflation at 5 dpf (169 ng/L) was similar to the LC50 value at 8 dpf (188 and 202 ng/L in two experiments). Interestingly, the patterns of delayed mortality and delayed effects on growth and development were similar between sole and zebrafish. This indicates the comparability of critical developmental stages across divergent fish species such as a cold water marine flatfish and a tropical freshwater cyprinid. Additionally, sublethal effects in early embryo-larval stages were found promising for predicting delayed lethal and sublethal effects of PCB126. Therefore, the proposed method with zebrafish is expected to provide valuable information on delayed mortality and delayed sublethal effects of chemicals and environmental samples that may be extrapolated to other species.

Evaluation and comparison of the relationship between NOEC and EC10 or EC20 values in chronic Daphnia toxicity testing

Hypothesis-based no-effect-concentration (NOEC) and regression-based x% effect concentration (ECx) values are common statistical approaches used to summarize ecotoxicological effects. Controversy over the NOEC model has prompted a movement toward discontinuation of the NOEC in favor of ECx, but the best x% effect surrogate for NOEC has not yet been determined. Historically, 10% and 20% effect concentrations (EC10 and EC20) have been treated as NOEC analogs. Given these measurements' importance to ecotoxicology, further understanding of the relationships between NOEC and EC10 or EC20 is crucial. In the present study, a metadataset of daphnid chronic toxicity tests was compiled to analyze the strength and significance of NOEC:EC10 and NOEC:EC20 relationships. The impact of endpoint (e.g., mortality, reproduction) and test condition parameters (e.g., pH, temperature) on NOEC:EC10 and NOEC:EC20 was evaluated. Mortality endpoints were most sensitive 51% of the time, with growth and reproductive endpoints constituting the remainder, underscoring the value of using multiple endpoints to evaluate toxic effects rather than relying on reproduction as the a priori most sensitive endpoint. When test condition parameters were less restricted (e.g., pH, hardness), the NOEC:EC20 association was more robust, suggesting that variability introduced by test implementation increased variability in ECx calculation. The analysis revealed that, overall, EC10 was a more suitable analog than EC20 for NOEC. Recommendations include refinement and reporting of the test parameters pH and hardness to minimize variability in ECx calculation.

The fish embryo toxicity test as a replacement for the larval growth and survival test: A comparison of test sensitivity and identification of alternative endpoints in zebrafish and fathead minnows

The fish embryo toxicity (FET) test has been proposed as an alternative to the larval growth and survival (LGS) test. The objectives of the present study were to evaluate the sensitivity of the FET and LGS tests in fathead minnows (Pimephales promelas) and zebrafish (Danio rerio) and to determine if the inclusion of sublethal metrics as test endpoints could enhance test utility. In both species, LGS and FET tests were conducted using 2 simulated effluents. A comparison of median lethal concentrations determined via each test revealed significant differences between test types; however, it could not be determined which test was the least and/or most sensitive. At the conclusion of each test, developmental abnormalities and the expression of genes related to growth and toxicity were evaluated. Fathead minnows and zebrafish exposed to mock municipal wastewater-treatment plant effluent in a FET test experienced an increased incidence of pericardial edema and significant alterations in the expression of genes including insulin-like growth factors 1 and 2, heat shock protein 70, and cytochrome P4501A, suggesting that the inclusion of these endpoints could enhance test utility. The results not only show the utility of the fathead minnow FET test as a replacement for the LGS test but also provide evidence that inclusion of additional endpoints could improve the predictive power of the FET test.

Alternative methods for toxicity assessments in fish: comparison of the fish embryo toxicity and the larval growth and survival tests in zebrafish and fathead minnows

An increased demand for chemical toxicity evaluations has resulted in the need for alternative testing strategies that address animal welfare concerns. The fish embryo toxicity (FET) test developed for zebrafish (Danio rerio) is one such alternative, and the application of the FET test to other species such as the fathead minnow (Pimephales promelas) has been proposed. In the present study, the performances of the FET test and the larval growth and survival (LGS; a standard toxicity testing method) test in zebrafish and fathead minnows were evaluated. This required that testing methods for the fathead minnow FET and zebrafish LGS tests be harmonized with existing test methods and that the performance of these testing strategies be evaluated by comparing the median lethal concentrations of 2 reference toxicants, 3,4-dicholoraniline and ammonia, obtained via each of the test types. The results showed that procedures for the zebrafish FET test can be adapted and applied to the fathead minnow. Differences in test sensitivity were observed for 3,4-dicholoraniline but not ammonia; therefore, conclusions regarding which test types offer the least or most sensitivity could not be made. Overall, these results show that the fathead minnow FET test has potential as an alternative toxicity testing strategy and that further analysis with other toxicants is warranted in an effort to better characterize the sensitivity and feasibility of this testing strategy.

Are acute and chronic saltwater fish studies required for plant protection and biocidal product active substance risk assessment?

The acute and chronic toxicity of chemicals to fish is routinely assessed using fish acute and early life stage (ELS) test results, usually with freshwater species. Under some regulations with certain substances, however, data on saltwater species may also be required. Evidence from earlier studies suggests that saltwater fish species are generally no more sensitive than freshwater species and that when they are more sensitive to a substance the difference in sensitivity is usually less than a factor of 10. However, most of these studies concentrated on acute lethal toxicity results for a wide range of substances and across a range of taxonomic groups. In the present study, the authors compare freshwater and saltwater acute median lethal concentration (LC50) and chronic ELS no-observed-effect concentration (NOEC) results from standardized regulatory studies specifically for fish species exposed to the same plant protection or biocidal product active substances to determine the value of testing in both freshwater and saltwater fish. The results suggest that, in most cases, use of a freshwater fish 96-h LC50 or longer-term ELS NOEC should be sufficient to protect saltwater species. In a small number of cases (12%), saltwater ELS NOECs were more sensitive by a factor >10, although differences in sensitivity were not consistent for this small number of substances when 96-h LC50 and longer-term ELS NOECs were compared. It is debatable whether such a low probability merits the additional animal use required to run saltwater fish tests, especially when onshore contaminants released to estuaries and coastal environments are likely to be diluted many-fold when compared with concentrations found in freshwaters.

Investigating alternatives to the fish early-life stage test: a strategy for discovering and annotating adverse outcome pathways for early fish development

The fish early-life stage (FELS) test (Organisation for Economic Co-operation and Development [OECD] test guideline 210) is the primary test used internationally to estimate chronic fish toxicity in support of ecological risk assessments and chemical management programs. As part of an ongoing effort to develop efficient and cost-effective alternatives to the FELS test, there is a need to identify and describe potential adverse outcome pathways (AOPs) relevant to FELS toxicity. To support this endeavor, the authors outline and illustrate an overall strategy for the discovery and annotation of FELS AOPs. Key events represented by major developmental landmarks were organized into a preliminary conceptual model of fish development. Using swim bladder inflation as an example, a weight-of-evidence-based approach was used to support linkage of key molecular initiating events to adverse phenotypic outcomes and reduced young-of-year survival. Based on an iterative approach, the feasibility of using key events as the foundation for expanding a network of plausible linkages and AOP knowledge was explored and, in the process, important knowledge gaps were identified. Given the scope and scale of the task, prioritization of AOP development was recommended and key research objectives were defined relative to factors such as current animal-use restrictions in the European Union and increased demands for fish toxicity data in chemical management programs globally. The example and strategy described are intended to guide collective efforts to define FELS-related AOPs and develop resource-efficient predictive assays that address the toxicological domain of the OECD 210 test.

Evaluation of the test of significant toxicity for determining the toxicity of effluents and ambient water samples

The test of significant toxicity (TST) is a hypothesis-testing approach based on bioequivalence developed by the U.S. Environmental Protection Agency (U.S. EPA) for analyzing whole-effluent toxicity (WET) and ambient toxicity data. The present study compares results of acute and chronic toxicity tests of effluent, storm-water, and ambient (i.e., receiving-water) samples using both the TST and the standard no-observed-effect concentration (NOEC) approach. Valid WET data were analyzed from 890 tests provided by more than 25 dischargers in California and Washington, USA, representing the majority of test methods used in the U.S. WET program. An additional 3,201 freshwater chronic toxicity tests, obtained from ambient monitoring programs in California, were also analyzed. The TST and NOEC approaches both declared a low number (<6.5%) of tests toxic if effects were below the unacceptable toxicity regulatory management decision (RMD) of 25% effect in chronic tests or 20% effect in acute tests. However, those test methods having generally lower within-test variability and greater test power (e.g., urchin fertilization test) had a much lower percentage of tests declared toxic than the NOEC approach when effects were below the unacceptable toxicity RMD. In addition, the TST showed fewer tests to be nontoxic than NOEC if the test exhibited effects greater than the toxicity RMD (0.1 and 9.6% for TST and NOEC, respectively, for effluents and 0 and 9.5%, respectively, for ambient samples). Our results demonstrate that the TST is more likely to identify a toxic sample when effects are fairly substantial (≥ 25% effect in chronic testing and ≥ 20% effect in acute tests) and less likely to identify a sample as toxic when effects are negligible (≤ 10% effect). Furthermore, these results demonstrate that appropriate WET data interpretation benefits from having well-designed test methods with sufficient power to identify significant toxicity or biologically insignificant effects when they occur.