REACH, non-testing approaches and the urgent need for a change in mind set

New approach methodologies in human regulatory toxicology - Not if, but how and when!

The predominantly animal-centric approach of chemical safety assessment has increasingly come under pressure. Society is questioning overall performance, sustainability, continued relevance for human health risk assessment and ethics of this system, demanding a change of paradigm. At the same time, the scientific toolbox used for risk assessment is continuously enriched by the development of "New Approach Methodologies" (NAMs). While this term does not define the age or the state of readiness of the innovation, it covers a wide range of methods, including quantitative structure-activity relationship (QSAR) predictions, high-throughput screening (HTS) bioassays, omics applications, cell cultures, organoids, microphysiological systems (MPS), machine learning models and artificial intelligence (AI). In addition to promising faster and more efficient toxicity testing, NAMs have the potential to fundamentally transform today's regulatory work by allowing more human-relevant decision-making in terms of both hazard and exposure assessment. Yet, several obstacles hamper a broader application of NAMs in current regulatory risk assessment. Constraints in addressing repeated-dose toxicity, with particular reference to the chronic toxicity, and hesitance from relevant stakeholders, are major challenges for the implementation of NAMs in a broader context. Moreover, issues regarding predictivity, reproducibility and quantification need to be addressed and regulatory and legislative frameworks need to be adapted to NAMs. The conceptual perspective presented here has its focus on hazard assessment and is grounded on the main findings and conclusions from a symposium and workshop held in Berlin in November 2021. It intends to provide further insights into how NAMs can be gradually integrated into chemical risk assessment aimed at protection of human health, until eventually the current paradigm is replaced by an animal-free "Next Generation Risk Assessment" (NGRA).

Unswerving modeling of hepatotoxicity of cadmium containing quantum dots using amalgamation of quasiSMILES, index of ideality of correlation, and consensus modeling

Liver toxicity of quantum dots varies with size, concentration, and other structural as well as experimental parameters. For modeling hepatotoxicity, the eclectic data associated with cadmium containing quantum dots have been used in the creation of quasiSMILES for their representation. The core diameter is normalized for wider applicability and the index of the ideality of correlation is applied to construct the better quantitative features toxicity relationship models. Total eight splits are created and the best model is obtained through split 1 with better prediction criteria of validation set objects. The values of all statistical criteria used in the quality determination of a QSAR model are within the specified range for all the eight toxicity models developed here. Factors like TGA ligand and 0.6-0.7 nm diameter are favorable for liver toxicity while L-cysteine ligand and 0.5-0.6 nm core diameter are helpful in the reduction of toxicity. Further, the intelligent consensus modeling process forms a total of 40 individual and 20 consensus models and the best individual and consensus models are 'Good' in MAE-based criteria. The consensus modeling enhances the prediction ability as well as the accuracy of the developed models and increases the applicability space of the built models for hepatotoxicity prediction of quantum dots.

Creating a human-induced pluripotent stem cell-based NKX2.5 reporter gene assay for developmental toxicity testing

To test large numbers of chemicals for developmental toxicity, rapid in vitro tests with standardized readouts for automated data acquisition are needed. However, the most widely used assay, the embryonic stem cell test, relies on the counting of beating embryoid bodies by visual inspection, which is laborious and time consuming. We previously developed the PluriBeat assay based on differentiation of human induced pluripotent stem cells (hiPSC) that we demonstrated to be predictive for known teratogens at relevant concentrations using the readout of beating cardiomyocytes. Here, we report the development of a novel assay, which we term the PluriLum assay, where we have introduced a luciferase reporter gene into the locus of NKX2.5 of our hiPSC line. This enabled us to measure luminescence intensities instead of counting beating cardiomyocytes, which is less labor intensive. We established two NKX2.5 reporter cell lines and validated their pluripotency and genetic stability. Moreover, we confirmed that the genetically engineered NKX2.5 reporter cell line differentiated into cardiomyocytes with the same efficiency as the original wild-type line. We then exposed the cells to valproic acid (25–300 μM) and thalidomide (0.1–36 µM) and compared the PluriBeat readout of the cardiomyocytes with the luminescence intensity of the PluriLum assay. The results showed that thalidomide decreased luminescence intensity significantly with a higher potency and efficacy compared to the beating readout. With this, we have developed a novel hiPSC-based assay with a standardized readout that may have the potential for higher throughput screening for developmental toxicity.

Differential uptake of and sensitivity to diphenhydramine in embryonic and larval zebrafish

The zebrafish fish embryo toxicity (FET) test is increasingly employed for alternative toxicity studies, yet our previous research identified increased sensitivity of zebrafish slightly older than embryos employed in FET methods (0-4 d postfertilization [dpf]). We identified rapid steady-state accumulation of diphenhydramine across zebrafish embryo and larval stages. However, significantly (p < 0.05) lower accumulation was observed at 48 h compared to 96 h in chorionated and dechorionated embryos (0-4 dpf), but not in zebrafish at 7 to 11 and 14 to 18 dpf. Increased uptake and toxicity of diphenhydramine was further observed in zebrafish at 7 to 11 and 14 to 18 dpf compared with 0-4 dpf embryos with chorion or dechorionated, which indicates that differential zebrafish sensitivity with age is associated with accumulation resulting from gill and other toxicokinetic and toxicodynamic changes during development. Environ Toxicol Chem 2018;37:1175-1181. © 2017 SETAC.

QSAR modeling of cumulative environmental end-points for the prioritization of hazardous chemicals

The hazard of chemicals in the environment is inherently related to the molecular structure and derives simultaneously from various chemical properties/activities/reactivities. Models based on Quantitative Structure Activity Relationships (QSARs) are useful to screen, rank and prioritize chemicals that may have an adverse impact on humans and the environment. This paper reviews a selection of QSAR models (based on theoretical molecular descriptors) developed for cumulative multivariate endpoints, which were derived by mathematical combination of multiple effects and properties. The cumulative end-points provide an integrated holistic point of view to address environmentally relevant properties of chemicals.

Quantitative Nanostructure-Activity Relationship Models for the Risk Assessment of NanoMaterials

In the last few decades, nanotechnology has been deeply established into human's everyday life with a great number of applications in cosmetics, textiles, electronics, optics, medicine, and many more. Although nanotechnology applications are rapidly increasing, the toxicity of some nanomaterials to living organisms and the environment still remains unknown and needs to be explored. The traditional toxicological evaluation of nanoparticles with the wide range of types, shapes, and sizes often involves expensive and time-consuming procedures. An efficient and cheap alternative is the development and application of predictive computational models using Quantitative Nanostructure-Activity Relationship (QNAR) methods. Towards this goal, researchers are mainly focused on the adverse effects of metal oxides and carbon nanotubes, but to date, QNAR studies are rare mainly because of the limited number of available organized datasets. In this chapter, recent studies for predictive QNAR models for the risk assessment of nanomaterials are reported and the perspectives of computational nanotoxicology that deeply relies on the intense collaboration between experimental and computational scientists are discussed.

Adaptation of the ToxRTool to Assess the Reliability of Toxicology Studies Conducted with Genetically Modified Crops and Implications for Future Safety Testing

To determine the reliability of food safety studies carried out in rodents with genetically modified (GM) crops, a Food Safety Study Reliability Tool (FSSRTool) was adapted from the European Centre for the Validation of Alternative Methods' (ECVAM) ToxRTool. Reliability was defined as the inherent quality of the study with regard to use of standardized testing methodology, full documentation of experimental procedures and results, and the plausibility of the findings. Codex guidelines for GM crop safety evaluations indicate toxicology studies are not needed when comparability of the GM crop to its conventional counterpart has been demonstrated. This guidance notwithstanding, animal feeding studies have routinely been conducted with GM crops, but their conclusions on safety are not always consistent. To accurately evaluate potential risks from GM crops, risk assessors need clearly interpretable results from reliable studies. The development of the FSSRTool, which provides the user with a means of assessing the reliability of a toxicology study to inform risk assessment, is discussed. Its application to the body of literature on GM crop food safety studies demonstrates that reliable studies report no toxicologically relevant differences between rodents fed GM crops or their non-GM comparators.

Development of Quantitative Structure-Activity Relationship Models for Predicting Chronic Toxicity of Substituted Benzenes to Daphnia Magna

The chronic toxicity of anthropogenic molecules such as substituted benzenes to Daphnia magna is a basic eco-toxicity parameter employed to assess their environmental risk. As the experimental methods are laborious, costly, and time-consuming, development in silico models for predicting the chronic toxicity is vitally important. In this study, on the basis of five molecular descriptors and 48 compounds, a quantitative structure-property relationship model that can predict the chronic toxicity of substituted benzenes were developed by employing multiple linear regressions. The correlation coefficient (R (2)) and root-mean square error (RMSE) for the training set were 0.836 and 0.390, respectively. The developed model was validated by employing 10 compounds tested in our lab. The R EXT (2) and RMSE EXT for the validation set were 0.736 and 0.490, respectively. To further characterizing the toxicity mechanism of anthropogenic molecules to Daphnia, comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) models were developed.

Modeling of Toxicity-Relevant Electrophilic Reactivity for Guanine with Epoxides: Estimating the Hard and Soft Acids and Bases (HSAB) Parameter as a Predictor

According to the electrophilic theory in toxicology, many chemical carcinogens in the environment and/or their active metabolites are electrophiles that exert their effects by forming covalent bonds with nucleophilic DNA centers. The theory of hard and soft acids and bases (HSAB), which states that a toxic electrophile reacts preferentially with a biological macromolecule that has a similar hardness or softness, clarifies the underlying chemistry involved in this critical event. Epoxides are hard electrophiles that are produced endogenously by the enzymatic oxidation of parent chemicals (e.g., alkenes and PAHs). Epoxide ring opening proceeds through a SN2-type mechanism with hard nucleophile DNA sites as the major facilitators of toxic effects. Thus, the quantitative prediction of chemical reactivity would enable a predictive assessment of the molecular potential to exert electrophile-mediated toxicity. In this study, we calculated the activation energies for reactions between epoxides and the guanine N7 site for a diverse set of epoxides, including aliphatic epoxides, substituted styrene oxides, and PAH epoxides, using a state-of-the-art density functional theory (DFT) method. It is worth noting that these activation energies for diverse epoxides can be further predicted by quantum chemically calculated nucleophilic indices from HSAB theory, which is a less computationally demanding method than the exacting procedure for locating the transition state. More importantly, the good qualitative/quantitative correlations between the chemical reactivity of epoxides and their bioactivity suggest that the developed model based on HSAB theory may aid in the predictive hazard evaluation of epoxides, enabling the early identification of mutagenicity/carcinogenicity-relevant SN2 reactivity.

Aqueous and tissue residue-based interspecies correlation estimation models provide conservative hazard estimates for aromatic compounds

Interspecies correlation estimation (ICE) models were developed for 30 nonpolar aromatic compounds to allow comparison of prediction accuracy between 2 data compilation approaches. Type 1 models used data combined across studies, and type 2 models used data combined only within studies. Target lipid (TLM) ICE models were also developed using target lipid concentrations of the type 2 model dataset (type 2-TLM). Analyses were performed to assess model prediction uncertainty introduced by each approach. Most statistically significant models (90%; 266 models total) had mean square errors < 0.27 and adjusted coefficients of determination (adj R(2) ) > 0.59, with the lowest amount of variation in mean square errors noted for type 2-TLM followed by type 2 models. Cross-validation success (>0.62) across most models (86% of all models) confirmed the agreement between ICE predicted and observed values. Despite differences in model predictive ability, most predicted values across all 3 ICE model types were within a 2-fold difference of the observed values. As a result, no statistically significant differences (p > 0.05) were found between most ICE-based and empirical species sensitivity distributions (SSDs). In most cases hazard concentrations were within or below the 95% confidence intervals of the direct-empirical SSD-based values, regardless of model choice. Interspecies correlation estimation-based 5th percentile (HC5) values showed a 200- to 900-fold increase as the log KOW increased from 2 to 5.3. Results indicate that ICE models for aromatic compounds provide a statistically based approach for deriving conservative hazard estimates for protecting aquatic life.

Age matters: Developmental stage of Danio rerio larvae influences photomotor response thresholds to diazinion or diphenhydramine

Because basic toxicological data is unavailable for the majority of industrial compounds, High Throughput Screening (HTS) assays using the embryonic and larval zebrafish provide promising approaches to define bioactivity profiles and identify potential adverse outcome pathways for previously understudied chemicals. Unfortunately, standardized approaches, including HTS experimental designs, for examining fish behavioral responses to contaminants are rarely available. In the present study, we examined movement behavior of larval zebrafish over 7 days (4-10 days post fertilization or dpf) during typical daylight workday hours to determine whether intrinsic activity differed with age and time of day. We then employed an early life stage approach using the Fish Embryo Test (FET) at multiple developmental ages to evaluate whether photomotor response (PMR) behavior differed with zebrafish age following exposure to diazinon (DZN), a well-studied orthophosphate insecticide, and diphenhydramine (DPH), an antihistamine that also targets serotonin reuptake transporters and the acetylcholine receptor. 72h studies were conducted at 1-4, 4-7 and 7-10dpf, followed by behavioral observations using a ViewPoint system at 4, 7 and 10dpf. Distance traveled and swimming speeds were quantified; nominal treatment levels were analytically verified by isotope-dilution LC-MSMS. Larval zebrafish locomotion displayed significantly different (p<0.05) activity profiles over the course of typical daylight and workday hours, and these time of day PMR activity profiles were similar across ages examined (4-10dpf). 10dpf zebrafish larvae were consistently more sensitive to DPH than either the 4 or 7dpf larvae with an environmentally realistic lowest observed effect concentration of 200ng/L. Though ELS and FET studies with zebrafish typically focus on mortality or teratogenicity in 0-4dpf organisms, behavioral responses of slightly older fish were several orders of magnitude more sensitive to DPH. Our observations highlight the importance of understanding the influence of time of day on intrinsic locomotor activity, and the age-specific hazards of aquatic contaminants to fish behavior.

Integrated Approaches to Testing and Assessment

In this chapter, we explain how Integrated Approaches to Testing and Assessment (IATA) offer a means of integrating and translating the data generated by toxicity testing methods, thereby serving as flexible and suitable tools for toxicological decision making in the twenty-first century. In addition to traditional in vitro and in vivo testing methods, IATA are increasingly incorporating newly developed in vitro systems and measurement technologies such as high throughput screening and high content imaging. Computational approaches are also being used in IATA development, both as a means of generating data (e.g. QSARs), interpreting data (bioinformatics and chemoinformatics), and as a means of integrating multiple sources of data (e.g. expert systems, bayesian models). Decision analytic methods derived from socioeconomic theory can also play a role in developing flexible and optimal IATA solutions. Some of the challenges involved in the development, validation and implementation of IATA are also discussed.

Investigation of the Verhaar scheme for predicting acute aquatic toxicity: improving predictions obtained from Toxtree ver. 2.6

Assessment of the potential of compounds to cause harm to the aquatic environment is an integral part of the REACH legislation. To reduce the number of vertebrate and invertebrate animals required for this analysis alternative approaches have been promoted. Category formation and read-across have been applied widely to predict toxicity. A key approach to grouping for environmental toxicity is the Verhaar scheme which uses rules to classify compounds into one of four mechanistic categories. These categories provide a mechanistic basis for grouping and any further predictive modelling. A computational implementation of the Verhaar scheme is available in Toxtree v2.6. The work presented herein demonstrates how modifications to the implementation of Verhaar between version 1.5 and 2.6 of Toxtree have improved performance by reducing the number of incorrectly classified compounds. However, for the datasets used in this analysis, version 2.6 classifies more compounds as outside of the domain of the model. Further amendments to the classification rules have been implemented here using a post-processing filter encoded as a KNIME workflow. This results in fewer compounds being classified as outside of the model domain, further improving the predictivity of the scheme. The utility of the modification described herein is demonstrated through building quality, mechanism-specific Quantitative Structure Activity Relationship (QSAR) models for the compounds within specific mechanistic categories.

Toxicology across scales: Cell population growth in vitro predicts reduced fish growth

Environmental risk assessment of chemicals is essential but often relies on ethically controversial and expensive methods. We show that tests using cell cultures, combined with modeling of toxicological effects, can replace tests with juvenile fish. Hundreds of thousands of fish at this developmental stage are annually used to assess the influence of chemicals on growth. Juveniles are more sensitive than adult fish, and their growth can affect their chances to survive and reproduce. Thus, to reduce the number of fish used for such tests, we propose a method that can quantitatively predict chemical impact on fish growth based on in vitro data. Our model predicts reduced fish growth in two fish species in excellent agreement with measured in vivo data of two pesticides. This promising step toward alternatives to fish toxicity testing is simple, inexpensive, and fast and only requires in vitro data for model calibration.

Analyzing precautionary regulation: do precaution, science, and innovation go together?

In this article we argue that the precautionary principle, as applied to the regulation of science and technology, cannot be considered in any general manner inconsistent with the norms and methods of scientific knowledge generation and justification. Moreover, it does not necessarily curtail scientific-technological innovation. Our argument flows from a differentiated view of what precaution in regulation means. We first characterize several of the most relevant interpretations given to the precautionary principle in academic debate and regulatory practice. We then use examples of actual precaution-based regulation to show that, even though science can have varying functions in different circumstances and frames, all of those interpretations recur to scientific method and knowledge, and tend to imply innovation in methods, products, and processes. In fact, the interplay of regulation and innovation in precautionary policy, at least in the case of the interpretations of precaution that our analysis takes into account, could be understood as a way of reconciling the two fundamental science and technology policy functions of promotion and control.

Regulatory acceptance and use of the Extended One Generation Reproductive Toxicity Study within Europe

The two-generation study (OECD TG 416) is the standard requirement within REACH to test reproductive toxicity effects of chemicals with production volumes >100 tonnes. This test is criticized in terms of scientific relevance and animal welfare. The Extended One Generation Reproductive Toxicity Study (EOGRTS), incorporated into the OECD test guidelines in 2011 (OECD TG 443) has the potential to replace TG 416, while using only one generation of rats and being more informative. However, its regulatory acceptance proved challenging. This article reconstructs the process of regulatory acceptance and use of the EOGRTS and describes drivers and barriers influencing the process. The findings derive from literature research and expert interviews. A distinction is made between three sub-stages; The stage of Formal Incorporation of the EOGRTS into OECD test guidelines was stimulated by retrospective analyses on the value of the second generation (F2), strong EOGRTS advocates, animal welfare concern and changing US and EU chemicals legislation; the stage of Actual Regulatory Acceptance within REACH was challenged by legal factors and ongoing scientific disputes, while the stage of Use by Industry is influenced by uncertainty of registrants about regulatory acceptance, high costs, the risk of false positives and the manageability of the EOGRTS.

Reducing aquatic hazards of industrial chemicals: probabilistic assessment of sustainable molecular design guidelines

Basic toxicological information is lacking for the majority of industrial chemicals. In addition to increasing empirical toxicity data through additional testing, prospective computational approaches to drug development aim to serve as a rational basis for the design of chemicals with reduced toxicity. Recent work has resulted in the derivation of a "rule of 2," wherein chemicals with an octanol-water partition coefficient (log P) less than 2 and a difference between the lowest unoccupied molecular orbital and the highest occupied molecular orbital (ΔE) greater than 9 (log P<2 and ΔE >9 eV) are predicted to be 4 to 5 times less likely to elicit acute or chronic toxicity to model aquatic organisms. The present study examines potential reduction of aquatic toxicity hazards from industrial chemicals if these 2 molecular design guidelines were employed. Probabilistic hazard assessment approaches were used to model the likelihood of encountering industrial chemicals exceeding toxicological categories of concern both with and without the rule of 2. Modeling predicted that utilization of these molecular design guidelines for log P and ΔE would appreciably decrease the number of chemicals that would be designated to be of "high" and "very high" concern for acute and chronic toxicity to standard model aquatic organisms and end points as defined by the US Environmental Protection Agency. For example, 14.5% of chemicals were categorized as having high and very high acute toxicity to the fathead minnow model, whereas only 3.3% of chemicals conforming to the design guidelines were predicted to be in these categories. Considerations of specific chemical classes (e.g., aldehydes), chemical attributes (e.g., ionization), and adverse outcome pathways in representative species (e.g., receptor-mediated responses) could be used to derive future property guidelines for broader classes of contaminants.

Building on a solid foundation: SAR and QSAR as a fundamental strategy to reduce animal testing

The development of more efficient, ethical, and effective means of assessing the effects of chemicals on human health and the environment was a lifetime goal of Gilman Veith. His work has provided the foundation for the use of chemical structure for informing toxicological assessment by regulatory agencies the world over. Veith's scientific work influenced the early development of the SAR models in use today at the US Environmental Protection Agency. He was the driving force behind the Organisation for Economic Co-operation and Development QSAR Toolbox. Veith was one of a few early pioneers whose vision led to the linkage of chemical structure and biological activity as a means of predicting adverse apical outcomes (known as a mode of action, or an adverse outcome pathway approach), and he understood at an early stage the power that could be harnessed when combining computational and mechanistic biological approaches as a means of avoiding animal testing. Through the International QSAR Foundation he organized like-minded experts to develop non-animal methods and frameworks for the assessment of chemical hazard and risk for the benefit of public and environmental health. Avoiding animal testing was Gil's passion, and his work helped to initiate the paradigm shift in toxicology that is now rendering this feasible.

Analysis of the ecotoxicity data submitted within the framework of the REACH Regulation. Part 3. Experimental sediment toxicity assays

For the first REACH registration deadline, companies have submitted registrations with relevant hazard and exposure information for substances at the highest tonnage level (above 1000 tonnes per year). At this tonnage level, information on the long-term toxicity of a substance to sediment organisms is required. There are a number of available test guidelines developed and accepted by various national/international organisations, which can be used to investigate long-term toxicity to sediment organisms. However instead of testing, registrants may also use other options to address toxicity to sediment organisms, e.g. weight of evidence approach, grouping of substances and read-across approaches, as well as substance-tailored exposure-driven testing. The current analysis of the data provided in ECHA database focuses on the test methods applied and the test organisms used in the experimental studies to assess long-term toxicity to sediment organisms. The main guidelines used for the testing of substances registered under REACH are the OECD guidelines and OSPAR Protocols on Methods for the Testing of Chemicals used in the Offshore Oil Industry: "Part A: A Sediment Bioassay using an Amphipod Corophium sp." explaining why one of the mostly used test organisms is the marine amphipod Corophium sp. In total, testing results with at least 40 species from seven phyla are provided in the database. However, it can be concluded that the ECHA database does not contain a high enough number of available experimental data on toxicity to sediment organisms for it to be used extensively by the scientific community (e.g. for development of non-testing methods to predict hazards to sediment organisms).

Analysis of the ecotoxicity data submitted within the framework of the REACH Regulation. Part 1. General overview and data availability for the first registration deadline

REACH(1) entered into force in June 2007 and has hence been operational for six years. With the first registration deadline in November 2010, the European Chemicals Agency (ECHA(2)) has received a large amount of scientific and administrative information related to chemical substances. In order to understand what type of data on ecotoxicity endpoints was submitted under the REACH framework a detailed analysis of the availability and content of relevant information was performed. To avoid unnecessary testing, the REACH Regulation provides registrants with the possibility to build testing strategies and to adopt the standard information requirements based on the specific conditions listed in the regulation. The types of information submitted by registrants to fulfil data requirements for aquatic, sediment and terrestrial toxicity endpoints were analysed. The REACH database analysis confirms large differences in the availability of experimental aquatic versus sediment and soil ecotoxicity data. Information requirements on aquatic organisms are mainly covered by experimental data, while those for sediment and soil are mostly waived.

Use of the Threshold of Toxicological Concern (TTC) approach for deriving target values for drinking water contaminants

Ongoing pollution and improving analytical techniques reveal more and more anthropogenic substances in drinking water sources, and incidentally in treated water as well. In fact, complete absence of any trace pollutant in treated drinking water is an illusion as current analytical techniques are capable of detecting very low concentrations. Most of the substances detected lack toxicity data to derive safe levels and have not yet been regulated. Although the concentrations in treated water usually do not have adverse health effects, their presence is still undesired because of customer perception. This leads to the question how sensitive analytical methods need to become for water quality screening, at what levels water suppliers need to take action and how effective treatment methods need to be designed to remove contaminants sufficiently. Therefore, in the Netherlands a clear and consistent approach called 'Drinking Water Quality for the 21st century (Q21)' has been developed within the joint research program of the drinking water companies. Target values for anthropogenic drinking water contaminants were derived by using the recently introduced Threshold of Toxicological Concern (TTC) approach. The target values for individual genotoxic and steroid endocrine chemicals were set at 0.01 μg/L. For all other organic chemicals the target values were set at 0.1 μg/L. The target value for the total sum of genotoxic chemicals, the total sum of steroid hormones and the total sum of all other organic compounds were set at 0.01, 0.01 and 1.0 μg/L, respectively. The Dutch Q21 approach is further supplemented by the standstill-principle and effect-directed testing. The approach is helpful in defining the goals and limits of future treatment process designs and of analytical methods to further improve and ensure the quality of drinking water, without going to unnecessary extents.

OSIRIS, a quest for proof of principle for integrated testing strategies of chemicals for four human health endpoints

Chemical substances policies in Europe are aiming towards chemical safety and at the same time a reduction in animal testing. These goals are alleged to be reachable by mining as many relevant data as possible, evaluate these data with regard to validity, reliability and relevance, and use of these data in so-called Integrated Testing Strategies (ITS). This paper offers an overview of four human health endpoints that were part of the EU-funded OSIRIS project, aiming to develop ITS fit for the EU chemicals legislation REACH. The endpoints considered cover their categorical as well as continuous characteristics: skin sensitisation, repeated dose toxicity, mutagenicity and carcinogenicity. Detailed papers are published elsewhere in this volume. The stepwise ITS approach developed takes advantage of existing information, groups information about similar substances and integrates exposure considerations. The different and possibly contradictory information is weighted and the respective uncertainties taken into account in a weight of evidence (WoE) approach. In case of data gaps, the ITS proposes the most appropriate method to acquire the missing information. Each building block for the ITS, i.e. each in vivo test, in vitro test, (Q)SAR model or human evidence, is evaluated with regard to quality.

Integrated testing strategies for safety assessments

Despite the fact that toxicology uses many stand-alone tests, a systematic combination of several information sources very often is required: Examples include: when not all possible outcomes of interest (e.g., modes of action), classes of test substances (applicability domains), or severity classes of effect are covered in a single test; when the positive test result is rare (low prevalence leading to excessive false-positive results); when the gold standard test is too costly or uses too many animals, creating a need for prioritization by screening. Similarly, tests are combined when the human predictivity of a single test is not satisfactory or when existing data and evidence from various tests will be integrated. Increasingly, kinetic information also will be integrated to make an in vivo extrapolation from in vitro data. Integrated Testing Strategies (ITS) offer the solution to these problems. ITS have been discussed for more than a decade, and some attempts have been made in test guidance for regulations. Despite their obvious potential for revamping regulatory toxicology, however, we still have little guidance on the composition, validation, and adaptation of ITS for different purposes. Similarly, Weight of Evidence and Evidence-based Toxicology approaches require different pieces of evidence and test data to be weighed and combined. ITS also represent the logical way of combining pathway-based tests, as suggested in Toxicology for the 21st Century. This paper describes the state of the art of ITS and makes suggestions as to the definition, systematic combination, and quality assurance of ITS.

Strategies for the optimisation of in vivo experiments in accordance with the 3Rs philosophy

There are a large number of chemicals in current use for which adequate toxicity data are not available. Whilst there are clear ethical and legal obligations to obtain data from sources other than in vivo experiments wherever possible, in certain cases in vivo assays may be deemed necessary. In such circumstances, it is essential to ensure that the maximum amount of high quality data is obtained from the minimum number of animals, using the most humane procedures, in accordance with the philosophy of reduction, refinement and replacement (3Rs). The aim of this report is to provide a strategy for anyone involved in animal experimentation, for either toxicological or pharmacological purposes, as to how in vivo experiments may be optimised. The impact of generic and endpoint specific sources of variability has been highlighted in a proof-of-principle analysis considering the variation in protocols for assays for four human health endpoints (skin sensitisation, reproductive/developmental toxicity, mutagenicity and carcinogenicity). Other factors such as operator training, experimental/statistical design, use of lower species and use of combined assays are also discussed. Recommendations for optimisation of in vivo assays, in terms of the 3Rs philosophy, applied to performing tests, harvesting data and appropriate reporting are summarised as a checklist of issues to be addressed prior to undertaking such assays.

Assessment of aquatic experimental versus predicted and extrapolated chronic toxicity data of four structural analogues

The present study was developed to assess the chronic toxicity predictions and extrapolations for a set of chlorinated anilines (aniline (AN), 4-chloroaniline (CA), 3,5-dichloroaniline (DCA) and 2,3,4-trichloroaniline (TCA)). Daphnia magna 21 d chronic experimental data was compared to the chronic toxicity predictions made by the US EPA ECOSAR QSAR tools and to acute-to-chronic extrapolations. Additionally, Species Sensitivity Distributions (SSDs) were constructed to assess the chronic toxicity variability among different species and to investigate the acute versus chronic toxicity in a multi-species context. Since chlorinated anilines are structural analogues with a designated polar narcotic mode of action, similar toxicity responses were assumed. However, rather large interchemical and interspecies differences in toxicity were observed. Compared to the other three test compounds, TCA exposure had a significantly larger impact on growth and reproduction of D. magna. Furthermore, this study illustrated that QSARs or a fixed ACR are not able to account for these interchemical and interspecies differences. Consequently, ECOSAR was found to be inadequate to predict the chronic toxicity of the anilines and the use of a fixed ACR (of 10) led to under of certain species. The experimental ACRs determined in D. magna were substantially different among the four aromatic amines (ACR of 32 for AN, 16.9 for CA, 5.7 for DCA and 60.8 for TCA). Furthermore, the SSDs illustrated that Danio rerio was rather insensitive to AN in comparison to another fish species, Phimphales promelas. It was therefore suggested that available toxicity data should be used in an integrative multi-species way, rather than using individual-based toxicity extrapolations. In this way, a relevant overview of the differences in species sensitivity is given, which in turn can serve as the basis for acute to chronic extrapolations.

Application of chemical toxicity distributions to ecotoxicology data requirements under REACH

The European Union's REACH regulation has further highlighted the lack of ecotoxicological data for substances in the marketplace. The mandates under REACH (registration, evaluation, authorization, and restriction of chemicals) to produce data and minimize testing on vertebrates present an impetus for advanced hazard assessment techniques using read-across. Research in our group has recently focused on probabilistic ecotoxicological hazard assessment approaches using chemical toxicity distributions (CTDs). Using available data for chemicals with similar modes of action or within a chemical class may allow for selection of a screening point value (SPV) for development of environmental safety values, based on a probabilistic distribution of toxicity values for a specific endpoint in an ecological receptor. Ecotoxicity data for acetylcholinesterase inhibitors and surfactants in Daphnia magna and Pimephales promelas were gathered from several data sources, including the U.S. Environmental Protection Agency's ECOTOX and Pesticides Ecotoxicity databases, the peer-reviewed literature, and the Human and Environmental Risk Assessment (HERA) project. Chemical toxicity distributions were subsequently developed, and the first and fifth centiles were used as SPVs for the development of screening-predicted no-effect concentrations (sPNECs). The first and fifth centiles of these distributions were divided by an assessment factor of 1,000, as recommended by REACH guidance. Use of screening values created using these techniques could support the processes of data dossier development and environmental exposure assessment, allowing for rigorous prioritization in testing and monitoring to fill data gaps.

In silico toxicology - non-testing methods

In silico toxicology in its broadest sense means “anything that we can do with a computer in toxicology.” Many different types of in silico methods have been developed to characterize and predict toxic outcomes in humans and environment. The term non-testing methods denote grouping approaches, structure–activity relationship, and expert systems. These methods are already used for regulatory purposes and it is anticipated that their role will be much more prominent in the near future. This Perspective will delineate the basic principles of non-testing methods and evaluate their role in current and future risk assessment of chemical compounds.

A discussion of the impact of US chemical regulation legislation on the field of toxicity testing

Proposals for revising the principal United States law governing industrial chemicals, the Toxic Substances Control Act, have been under consideration in the US Congress for the past several years, and some version of such legislation may be passed in the near future. Concurrently, a desire to move away from current testing methods for ethical, scientific, and practical reasons has led to multi-million dollar investments in in vitro and computational toxicology methods and programs. Legislative language has the potential to endorse this transition and facilitate its fruition, or conversely enshrine in vivo testing methods for the foreseeable future. New legislation also has the potential to substantially increase the numbers of animals used in toxicity tests in the near term. However, there are a number of policies that, used effectively, can reduce the overall number of animals used in new toxicity tests. We present recent legislative proposals in the context of current testing programs and discuss their potential impacts on animal use, test method innovation, and achievement of desired legislative objectives. Discussions like these are essential to judiciously select policies that reduce the use of animals in toxicity testing and protect human health and the environment.

Alternative (non-animal) methods for cosmetics testing: current status and future prospects-2010

The 7th amendment to the EU Cosmetics Directive prohibits to put animal-tested cosmetics on the market in Europe after 2013. In that context, the European Commission invited stakeholder bodies (industry, non-governmental organisations, EU Member States, and the Commission's Scientific Committee on Consumer Safety) to identify scientific experts in five toxicological areas, i.e. toxicokinetics, repeated dose toxicity, carcinogenicity, skin sensitisation, and reproductive toxicity for which the Directive foresees that the 2013 deadline could be further extended in case alternative and validated methods would not be available in time. The selected experts were asked to analyse the status and prospects of alternative methods and to provide a scientifically sound estimate of the time necessary to achieve full replacement of animal testing. In summary, the experts confirmed that it will take at least another 7-9 years for the replacement of the current in vivo animal tests used for the safety assessment of cosmetic ingredients for skin sensitisation. However, the experts were also of the opinion that alternative methods may be able to give hazard information, i.e. to differentiate between sensitisers and non-sensitisers, ahead of 2017. This would, however, not provide the complete picture of what is a safe exposure because the relative potency of a sensitiser would not be known. For toxicokinetics, the timeframe was 5-7 years to develop the models still lacking to predict lung absorption and renal/biliary excretion, and even longer to integrate the methods to fully replace the animal toxicokinetic models. For the systemic toxicological endpoints of repeated dose toxicity, carcinogenicity and reproductive toxicity, the time horizon for full replacement could not be estimated.

Bacterial gene profiling assay applied as an alternative method for mode of action classification: pilot study using chlorinated anilines

Polar narcotic structural analogues (e.g., chlorinated anilines with a differing degree of chlorosubstitution, such as aniline, 4-chloroaniline, 3,5-dichloroaniline, and 2,3,4-trichloroaniline) are assumed to induce their toxic effects via the same predominant mode of action (MOA; membrane damage) at equitoxic exposure concentrations. In this study, a bacterial gene profiling assay consisting of 14 general stress genes was used to test this hypothesis for these four compounds. Although we found a consistent induction of membrane damage, the response cascade and the extent of the response differed among the different chemical treatments. The higher chlorosubstituted anilines also triggered significantly more genes involved in other general stress MOA classes (oxidative stress and protein perturbation). These findings illustrate that, along with the commonly used physicochemistry-based MOA categorization methods, alternative tests such as the bacterial gene profiling assay can yield valuable biological information on the MOA of a certain chemical or group of chemicals that is crucial in high-quality environmental risk assessment. In a second phase, the experimental gene profiling data sets of the chlorinated anilines were analyzed and weighed against existing data on other polar and non polar narcotic compounds to obtain a broader comparison in which the predefined chemical MOAs (narcosis and polar narcosis) were contrasted with the biological MOAs (gene expression profiles). Although additional optimization of the assay is needed, our results show that the bacterial gene profiling assay opens new perspectives for biology-based chemical grouping, thereby further enabling targeted MOA-based risk assessment.

A review of the electrophilic reaction chemistry involved in covalent DNA binding

The need to assess the ability of a chemical to act as a mutagen or a genotoxic carcinogen (collectively termed genotoxicity) is one of the primary requirements in regulatory toxicology. Several pieces of legislation have led to an increased interest in the use of in silico methods, specifically the formation of chemical categories for the assessment of toxicological endpoints. A key step in the development of chemical categories for genotoxicity is defining the organic chemistry associated with the formation of a covalent bond between DNA and an exogenous chemical. This organic chemistry is typically defined as structural alerts. To this end, this article has reviewed the literature defining the structural alerts associated with covalent DNA binding. Importantly, this review article also details the mechanistic organic chemistry associated with each of the structural alerts. This information is extremely important in terms of meeting regulatory requirements for the acceptance of the chemical category approach. The structural alerts and associated mechanistic chemistry have been incorporated into the Organisation for Economic Co-operation and Development (OECD) (Q)SAR Application Toolbox.

Characterisation, Evaluation and Possible Validation of In Silico Models for Toxicity: Determining if a Prediction is Valid

This chapter describes the process whereby a (Q)SAR may be described, evaluated and, where possible, validated. The emphasis here is not to develop models, but to characterise them according to the guidance supplied by the Organisation for Economic Co-operation and Development (OECD) and the European Chemicals Agency (EChA). The backbone to this process are the OECD Principles for the Validation of (Q)SARs. Three case studies illustrating how to approach the OECD Principles are supplied.

Examination of Michael addition reactivity towards glutathione by transition-state calculations

Kinetic rate constants (k(GSH)) for the reaction of compounds acting as Michael acceptors with glutathione (GSH) were modelled by quantum chemical transition-state calculations at the B3LYP/6-31G** and B3LYP/TZVP level. The data set included α, β-unsaturated aldehydes, ketones and esters, with double bonds and triple bonds, linear and cyclic systems, both with and without substituents in the α-position. Predicted values for k(GSH) were found to be in good agreement with experimental k(GSH) values. Factors affecting rate constants have been elucidated, especially solvent effects and the influence of steric hindrance. Solvent effects were examined by adding explicit solvent molecules to the system and by using a polarizable continuum solvent model. Detailed analysis of transition-state energies shows that the reaction is reversible. The reactive enolic intermediate plays an important role in Michael addition to GSH, while the subsequent keto-enol-tautomerism is not rate limiting.

Beyond REACH: roadblocks and shortcuts en route to integrated risk assessment and management of chemicals

This paper addresses obstacles and opportunities for the development and application of novel methods for integrated assessment of cumulative risks from chemicals, exemplified by the REACH legislation of the EU, in the context of multiple stressors and of chemicals policy. We examine the role of such methods in connection with REACH by models of integration and innovation of risk information in multi-actor risk governance; analyses of key documents on REACH; and interviews with EU regulators and stakeholders. We first explain the emergence of REACH as a response to tensions in EU chemicals, environmental and other policies. We then analyze the present configuration of REACH particularly in relation to key dimensions of risk integration: across stressors; exposed organisms; and impacts. Among the policy aspects of integrated risk information, we focus on its interaction with management and the contesting framings and interpretations of assessment. Avenues and barriers are identified for integrated treatment of risks under REACH and with other instruments. We emphasize how bounded, formal and static assessments interact with open and informal approaches that have more flexibility in integrating risks in new ways. We conclude with a generalizing discussion on the role of novel methods of integrated risk assessment in the development of reflexive and participatory governance under REACH and beyond.