Canadian Regulatory Perspective on Next Generation Risk Assessments for Pest Control Products and Industrial Chemicals

Key attributes of health and environmental risk decision-making: A scoping review

Government agencies, international institutions, and independent experts have published approaches for the assessment and management of health and environmental risks. This includes evidence-based strategies and publications supporting risk decision-making frameworks reflecting contemporary practices, the overarching context, and governance structures for addressing known and emerging risk issues. This scoping review surveys the literature, over the last five decades, to identify key attributes of health and environmental risk decision-making and how these inherent characteristics are related to the overarching regulatory decision-making context. The findings provide insights on how these publications accounted for the circumstances and triggers at that time. This includes incorporating factors reflecting advances in science and technology, a better understanding of underlying values (e.g., societal), and an expansion in the scope and complexity required for conducting different evaluations relevant to health and environmental risks. Consequently, the evolution from linear to more expanded and holistic decision-making frameworks incorporates foundational elements, such as the well-established steps for assessing risks, while adding aspects reflecting transformative changes and paradigm shifts (e.g., the use of non-animal testing strategies for evaluating human safety). Our analysis also resulted in the generation of a consolidated listing of ten attributes: trigger/issue, regulatory context, regulatory factors, core values, risk decision-making principles, cross-cutting attributes, design (scope and steps), structure, decision-making pathway, and evidence-knowledge requirements for risk decision-making. A better understanding of this evolution in risk decision-making and the listing of key attributes will be used in future work aimed at developing considerations for next generation decision-making approaches for health and environmental risks.

Bioinformatic workflows for deriving transcriptomic points of departure: current status, data gaps, and research priorities

There is a pressing need to increase the efficiency and reliability of toxicological safety assessment for protecting human health and the environment. Although conventional toxicology tests rely on measuring apical changes in vertebrate models, there is increasing interest in the use of molecular information from animal and in vitro studies to inform safety assessment. One promising and pragmatic application of molecular information involves the derivation of transcriptomic points of departure (tPODs). Transcriptomic analyses provide a snapshot of global molecular changes that reflect cellular responses to stressors and progression toward disease. A tPOD identifies the dose level below which a concerted change in gene expression is not expected in a biological system in response to a chemical. A common approach to derive such a tPOD consists of modeling the dose-response behavior for each gene independently and then aggregating the gene-level data into a single tPOD. Although different implementations of this approach are possible, as discussed in this manuscript, research strongly supports the overall idea that reference doses produced using tPODs are health protective. An advantage of this approach is that tPODs can be generated in shorter term studies (e.g. days) compared with apical endpoints from conventional tests (e.g. 90-d subchronic rodent tests). Moreover, research strongly supports the idea that reference doses produced using tPODs are health protective. Given the potential application of tPODs in regulatory toxicology testing, rigorous and reproducible wet and dry laboratory methodologies for their derivation are required. This review summarizes the current state of the science regarding the study design and bioinformatics workflows for tPOD derivation. We identify standards of practice and sources of variability in tPOD generation, data gaps, and areas of uncertainty. We provide recommendations for research to address barriers and promote adoption in regulatory decision making.

Signature analysis of high-throughput transcriptomics screening data for mechanistic inference and chemical grouping

High-throughput transcriptomics (HTTr) uses gene expression profiling to characterize the biological activity of chemicals in in vitro cell-based test systems. As an extension of a previous study testing 44 chemicals, HTTr was used to screen an additional 1,751 unique chemicals from the EPA's ToxCast collection in MCF7 cells using 8 concentrations and an exposure duration of 6 h. We hypothesized that concentration-response modeling of signature scores could be used to identify putative molecular targets and cluster chemicals with similar bioactivity. Clustering and enrichment analyses were conducted based on signature catalog annotations and ToxPrint chemotypes to facilitate molecular target prediction and grouping of chemicals with similar bioactivity profiles. Enrichment analysis based on signature catalog annotation identified known mechanisms of action (MeOAs) associated with well-studied chemicals and generated putative MeOAs for other active chemicals. Chemicals with predicted MeOAs included those targeting estrogen receptor (ER), glucocorticoid receptor (GR), retinoic acid receptor (RAR), the NRF2/KEAP/ARE pathway, AP-1 activation, and others. Using reference chemicals for ER modulation, the study demonstrated that HTTr in MCF7 cells was able to stratify chemicals in terms of agonist potency, distinguish ER agonists from antagonists, and cluster chemicals with similar activities as predicted by the ToxCast ER Pathway model. Uniform manifold approximation and projection (UMAP) embedding of signature-level results identified novel ER modulators with no ToxCast ER Pathway model predictions. Finally, UMAP combined with ToxPrint chemotype enrichment was used to explore the biological activity of structurally related chemicals. The study demonstrates that HTTr can be used to inform chemical risk assessment by determining in vitro points of departure, predicting chemicals' MeOA and grouping chemicals with similar bioactivity profiles.

Synthetic vitreous fibers (SVFs): adverse outcome pathways (AOPs) and considerations for next generation new approach methods (NAMs)

Fiber dimension, durability/dissolution, and biopersistence are critical factors for the risk of fibrogenesis and carcinogenesis. In the modern era, to reduce, refine, and replace animals in toxicology research, the application of in vitro test methods is paramount for hazard evaluation and designing synthetic vitreous fibers (SVFs) for safe use. The objectives of this review are to: (1) summarize the international frameworks and acceptability criteria for implementation of new approach methods (NAMs), (2) evaluate the adverse outcome pathways (AOPs), key events (KEs), and key event relationships (KERs) for fiber-induced fibrogenesis and carcinogenesis in accordance with Organization for Economic Co-operation and Development (OECD) guidelines, (3) consider existing and emerging technologies for in silico and in vitro toxicity testing for the respiratory system and the ability to predict effects in vivo, (4) outline a recommended testing strategy for evaluating the hazard and safety of novel SVFs, and (5) reflect on methods needs for in vitro in vivo correlation (IVIVC) and predictive approaches for safety assessment of new SVFs. AOP frameworks following the conceptual model of the OECD were developed through an evaluation of available molecular and cellular initiating events, which lead to KEs and KERs in the development of fiber-induced fibrogenesis and carcinogenesis. AOP framework development included consideration of fiber physicochemical properties, respiratory deposition and clearance patterns, biosolubility, and biopersistence, as well as cellular, organ, and organism responses. Available data support that fiber AOPs begin with fiber physicochemical characteristics which influence fiber exposure and biosolubility and subsequent key initiating events are dependent on fiber biopersistence and reactivity. Key cellular events of pathogenic fibers include oxidative stress, chronic inflammation, and epithelial/fibroblast proliferation and differentiation, which ultimately lead to hyperplasia, metaplasia, and fibrosis/tumor formation. Available in vitro models (e.g. single-, multi-cellular, organ system) provide promising NAMs tools to evaluate these intermediate KEs. However, data on SVFs demonstrate that in vitro biosolubility is a reasonable predictor for downstream events of in vivo biopersistence and biological effects. In vitro SVF fiber dissolution rates >100 ng/cm2/hr (glass fibers in pH 7 and stone fibers in pH 4.5) and in vivo SVF fiber clearance half-life less than 40 or 50 days were not associated with fibrosis or tumors in animals. Long (fiber lengths >20 µm) biodurable and biopersistent fibers exceeding these fiber dissolution and clearance thresholds may pose a risk of fibrosis and cancer. In vitro fiber dissolution assays provide a promising avenue and potentially powerful tool to predict in vivo SVF fiber biopersistence, hazard, and health risk. NAMs for fibers (including SVFs) may involve a multi-factor in vitro approach leveraging in vitro dissolution data in complement with cellular- and tissue- based in vitro assays to predict health risk.

Building knowledge of NAMs through risk science

The 12th World Congress on Alternatives and Animal Use in the Life Sciences provided a platform for mobilizing and exchanging knowledge on the advancements in science and technology. It also provided an opportunity for experts to discuss how to accelerate the adoption of new strategies and tools. One of these recommendations advocated the need to bridge the gap between the next generation of scientists who have yet to learn about 'New Approach Methodologies' (NAMs) and the current generation of thought leaders who have pioneered the development and validation of these non-animal approaches to toxicological risk assessment. Consequently, a mini-course, held at Canada's University of Ottawa, was developed for students, aged 13-16 years, interested in learning about risk science and how NAMs can be used to inform human health risk assessment. This course also served as a platform for creating a virtual training roadmap, provided in this paper, thereby bringing this knowledge to a broader audience of learners who are establishing their careers in the field of risk science.

Relevance and feasibility of principles for health and environmental risk decision-making

Globally, national regulatory authorities are both responsible and accountable for health and environmental decisions related to diverse products and risk decision contexts. These authorities provided regulatory oversight and expedited market authorizations of vaccines and other therapeutic products during the COVID-19 pandemic. Regulatory decisions regarding such products and situations depend upon well-established risk assessment and management steps. The underlying processes supporting such decisions were outlined in frameworks describing the complex interactions between factors including risk assessment and management steps as well as principles which help guide risk decision-making. In 2022, experts in risk science proposed a set of 10 guiding principles, further examining the intersection and utility of these principles using 10 diverse risk contexts, and inviting a broader discourse on the application of these principles in risk decision-making. To add to this information, Canadian regulatory practitioners responsible for evaluating health and environmental risks and establishing policies convened at a Health Canada workshop on Principles for Risk Decision-Making. This review reports the results derived from this interactive engagement and provides a first pragmatic analysis of the relevance, importance, and feasibility of such principles for health and environmental risk decision-making within the Canadian regulatory context.

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

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

Comparative deterministic and probabilistic approaches for assessing the aquatic ecological risk of pesticides in a mixed land use basin: A case study in Uruguay

Environmental concentrations of 25 pesticides in superficial water were employed to conduct an ecological risk assessment (ERA) in a mixed land-use basin utilized as a drinking water source. A deterministic risk assessment (RQ) was utilized to evaluate the chronic risk to aquatic biota, while a probabilistic risk assessment (PRA) approach was applied to assess the acute and chronic risk in the most sensitive species and at the community level. A high risk was identified for insecticides (pyrethroids, organophosphates and organochlorines). RQs ranged from 4.0e-4 (2,4-D) to 105.3 (ethion) considering median concentrations and from 8.0e-4 (2,4-D) to 230 (p,p'-DDT) considering extreme concentrations. Temporal variation in ΣRQs showed the highest risk during spring and summer months, which is related to the crop calendar and land use in the Laguna del Cisne basin. For PRA, the probability of exceeding the hazardous concentration HC5 (5th percentile) was higher for the most sensitive species in chronic exposure, especially for cypermethrin (38.9 %), permethrin (25.6 %), and chlorpyrifos (16.6 %). In the case of acute exposures, the probability of surpassing HC5 was higher for the entire freshwater biota, with the highest values observed for bifenthrin (28.3 %), cypermethrin (25.5 %), permethrin (11.75 %), and ethion (11.1 %). The advantages and disadvantages of PRA for assessing pesticide ecological risk were compared with the conventional deterministic RQs approach, highlighting that PRA offers improvements over the deterministic risk assessment, especially for organophosphate pesticides. Additionally, PRA provides a more comprehensive evaluation of risk for both short and long-term exposure, has the potential to incorporate others available toxicity data (e.g., LD50, Daily Intake), and utilizes different hazardous concentrations, such as HC5, HC10, and HC50. Our findings emphasize the urgent need to establish a national regulatory framework to evaluate and mitigate pesticide risks in aquatic ecosystems, especially in drinking water source like Laguna del Cisne.

Reproducibility of organ-level effects in repeat dose animal studies

This work estimates benchmarks for new approach method (NAM) performance in predicting organ-level effects in repeat dose studies of adult animals based on variability in replicate animal studies. Treatment-related effect values from the Toxicity Reference database (v2.1) for weight, gross, or histopathological changes in the adrenal gland, liver, kidney, spleen, stomach, and thyroid were used. Rates of chemical concordance among organ-level findings in replicate studies, defined by repeated chemical only, chemical and species, or chemical and study type, were calculated. Concordance was 39 - 88%, depending on organ, and was highest within species. Variance in treatment-related effect values, including lowest effect level (LEL) values and benchmark dose (BMD) values when available, was calculated by organ. Multilinear regression modeling, using study descriptors of organ-level effect values as covariates, was used to estimate total variance, mean square error (MSE), and root residual mean square error (RMSE). MSE values, interpreted as estimates of unexplained variance, suggest study descriptors accounted for 52-69% of total variance in organ-level LELs. RMSE ranged from 0.41 - 0.68 log10-mg/kg/day. Differences between organ-level effects from chronic (CHR) and subchronic (SUB) dosing regimens were also quantified. Odds ratios indicated CHR organ effects were unlikely if the SUB study was negative. Mean differences of CHR - SUB organ-level LELs ranged from -0.38 to -0.19 log10 mg/kg/day; the magnitudes of these mean differences were less than RMSE for replicate studies. Finally, in vitro to in vivo extrapolation (IVIVE) was employed to compare bioactive concentrations from in vitro NAMs for kidney and liver to LELs. The observed mean difference between LELs and mean IVIVE dose predictions approached 0.5 log10-mg/kg/day, but differences by chemical ranged widely. Overall, variability in repeat dose organ-level effects suggests expectations for quantitative accuracy of NAM prediction of LELs should be at least ± 1 log10-mg/kg/day, with qualitative accuracy not exceeding 70%.

Human cell-based in vitro systems to assess respiratory toxicity: a case study using silanes

Inhalation is a major route by which human exposure to substances can occur. Resources have therefore been dedicated to optimize human-relevant in vitro approaches that can accurately and efficiently predict the toxicity of inhaled chemicals for robust risk assessment and management. In this study-the IN vitro Systems to PredIct REspiratory toxicity Initiative-2 cell-based systems were used to predict the ability of chemicals to cause portal-of-entry effects on the human respiratory tract. A human bronchial epithelial cell line (BEAS-2B) and a reconstructed human tissue model (MucilAir, Epithelix) were exposed to triethoxysilane (TES) and trimethoxysilane (TMS) as vapor (mixed with N2 gas) at the air-liquid interface. Cell viability, cytotoxicity, and secretion of inflammatory markers were assessed in both cell systems and, for MucilAir tissues, morphology, barrier integrity, cilia beating frequency, and recovery after 7 days were also examined. The results show that both cell systems provide valuable information; the BEAS-2B cells were more sensitive in terms of cell viability and inflammatory markers, whereas MucilAir tissues allowed for the assessment of additional cellular effects and time points. As a proof of concept, the data were also used to calculate human equivalent concentrations. As expected, based on chemical properties and existing data, the silanes demonstrated toxicity in both systems with TMS being generally more toxic than TES. Overall, the results demonstrate that these in vitro test systems can provide valuable information relevant to predicting the likelihood of toxicity following inhalation exposure to chemicals in humans.

The ToxCast pipeline: updates to curve-fitting approaches and database structure

Introduction: The US Environmental Protection Agency Toxicity Forecaster (ToxCast) program makes in vitro medium- and high-throughput screening assay data publicly available for prioritization and hazard characterization of thousands of chemicals. The assays employ a variety of technologies to evaluate the effects of chemical exposure on diverse biological targets, from distinct proteins to more complex cellular processes like mitochondrial toxicity, nuclear receptor signaling, immune responses, and developmental toxicity. The ToxCast data pipeline (tcpl) is an open-source R package that stores, manages, curve-fits, and visualizes ToxCast data and populates the linked MySQL Database, invitrodb. Methods: Herein we describe major updates to tcpl and invitrodb to accommodate a new curve-fitting approach. The original tcpl curve-fitting models (constant, Hill, and gain-loss models) have been expanded to include Polynomial 1 (Linear), Polynomial 2 (Quadratic), Power, Exponential 2, Exponential 3, Exponential 4, and Exponential 5 based on BMDExpress and encoded by the R package dependency, tcplfit2. Inclusion of these models impacted invitrodb (beta version v4.0) and tcpl v3 in several ways: (1) long-format storage of generic modeling parameters to permit additional curve-fitting models; (2) updated logic for winning model selection; (3) continuous hit calling logic; and (4) removal of redundant endpoints as a result of bidirectional fitting. Results and discussion: Overall, the hit call and potency estimates were largely consistent between invitrodb v3.5 and 4.0. Tcpl and invitrodb provide a standard for consistent and reproducible curve-fitting and data management for diverse, targeted in vitro assay data with readily available documentation, thus enabling sharing and use of these data in myriad toxicology applications. The software and database updates described herein promote comparability across multiple tiers of data within the US Environmental Protection Agency CompTox Blueprint.

Regulatory landscape of alternatives to animal testing in food safety evaluations with a focus on the western world

Traditional animal models are increasingly being replaced by new approach methodologies (NAMs) which focus on predicting toxicity of chemicals based on mechanistic data rather than apical endpoint data usually obtained from animal models. Beyond in vitro genetic tests, however, only a handful of NAMs have been successfully implemented in regulatory decision-making processes, mostly in the cosmetics and chemicals sector. Regulatory guidance on food safety testing in many jurisdictions still relies on data obtained from animal studies. This is due to the lack of validated models to predict systemic toxicity, which is essential to develop health-based guidance values for food additives. Other factors limiting the adoption of NAMs into food safety assessment include sector legislation lagging behind scientific progress, and lack of training and expertise to use the new models. While regulatory and industry bodies are working to combat these challenges, more needs to be done before these models can be used as standalone tools for regulatory decision-making. This review summarizes the current state and challenges of regulatory acceptance of NAMs for decision-making, and the efforts by governing bodies and industry to transition from animal testing for food safety assessments.

From vision toward best practices: Evaluating in vitro transcriptomic points of departure for application in risk assessment using a uniform workflow

The growing number of chemicals in the current consumer and industrial markets presents a major challenge for regulatory programs faced with the need to assess the potential risks they pose to human and ecological health. The increasing demand for hazard and risk assessment of chemicals currently exceeds the capacity to produce the toxicity data necessary for regulatory decision making, and the applied data is commonly generated using traditional approaches with animal models that have limited context in terms of human relevance. This scenario provides the opportunity to implement novel, more efficient strategies for risk assessment purposes. This study aims to increase confidence in the implementation of new approach methods in a risk assessment context by using a parallel analysis to identify data gaps in current experimental designs, reveal the limitations of common approaches deriving transcriptomic points of departure, and demonstrate the strengths in using high-throughput transcriptomics (HTTr) to derive practical endpoints. A uniform workflow was applied across six curated gene expression datasets from concentration-response studies containing 117 diverse chemicals, three cell types, and a range of exposure durations, to determine tPODs based on gene expression profiles. After benchmark concentration modeling, a range of approaches was used to determine consistent and reliable tPODs. High-throughput toxicokinetics were employed to translate in vitro tPODs (µM) to human-relevant administered equivalent doses (AEDs, mg/kg-bw/day). The tPODs from most chemicals had AEDs that were lower (i.e., more conservative) than apical PODs in the US EPA CompTox chemical dashboard, suggesting in vitro tPODs would be protective of potential effects on human health. An assessment of multiple data points for single chemicals revealed that longer exposure duration and varied cell culture systems (e.g., 3D vs. 2D) lead to a decreased tPOD value that indicated increased chemical potency. Seven chemicals were flagged as outliers when comparing the ratio of tPOD to traditional POD, thus indicating they require further assessment to better understand their hazard potential. Our findings build confidence in the use of tPODs but also reveal data gaps that must be addressed prior to their adoption to support risk assessment applications.

Application of ToxCast/Tox21 data for toxicity mechanism-based evaluation and prioritization of environmental chemicals: Perspective and limitations

In response to the need to minimize the use of experimental animals, new approach methodologies (NAMs) using advanced technology have emerged in the 21st century. ToxCast/Tox21 aims to evaluate the adverse effects of chemicals quickly and efficiently using a high-throughput screening and to transform the paradigm of toxicity assessment into mechanism-based toxicity prediction. The ToxCast/Tox21 database, which contains extensive data from over 1400 assays with numerous biological targets and activity data for over 9000 chemicals, can be used for various purposes in the field of chemical prioritization and toxicity prediction. In this study, an overview of the database was explored to aid mechanism-based chemical prioritization and toxicity prediction. Implications for the utilization of the ToxCast/Tox21 database in chemical prioritization and toxicity prediction were derived. The research trends in ToxCast/Tox21 assay data were reviewed in the context of toxicity mechanism identification, chemical priority, environmental monitoring, assay development, and toxicity prediction. Finally, the potential applications and limitations of using ToxCast/Tox21 assay data in chemical risk assessment were discussed. The analysis of the toxicity mechanism-based assays of ToxCast/Tox21 will help in chemical prioritization and regulatory applications without the use of laboratory animals.

Use of new approach methodologies (NAMs) to meet regulatory requirements for the assessment of industrial chemicals and pesticides for effects on human health

New approach methodologies (NAMs) are increasingly being used for regulatory decision making by agencies worldwide because of their potential to reliably and efficiently produce information that is fit for purpose while reducing animal use. This article summarizes the ability to use NAMs for the assessment of human health effects of industrial chemicals and pesticides within the United States, Canada, and European Union regulatory frameworks. While all regulations include some flexibility to allow for the use of NAMs, the implementation of this flexibility varies across product type and regulatory scheme. This article provides an overview of various agencies' guidelines and strategic plans on the use of NAMs, and specific examples of the successful application of NAMs to meet regulatory requirements. It also summarizes intra- and inter-agency collaborations that strengthen scientific, regulatory, and public confidence in NAMs, thereby fostering their global use as reliable and relevant tools for toxicological evaluations. Ultimately, understanding the current regulatory landscape helps inform the scientific community on the steps needed to further advance timely uptake of approaches that best protect human health and the environment.

Rethinking chronic toxicity and carcinogenicity assessment for agrochemicals project (ReCAAP): A reporting framework to support a weight of evidence safety assessment without long-term rodent bioassays

Rodent cancer bioassays have been long-required studies for regulatory assessment of human cancer hazard and risk. These studies use hundreds of animals, are resource intensive, and certain aspects of these studies have limited human relevance. The past 10 years have seen an exponential growth of new technologies with the potential to effectively evaluate human cancer hazard and risk while reducing, refining, or replacing animal use. To streamline and facilitate uptake of new technologies, a workgroup comprised of scientists from government, academia, non-governmental organizations, and industry stakeholders developed a framework for waiver rationales of rodent cancer bioassays for consideration in agrochemical safety assessment. The workgroup used an iterative approach, incorporating regulatory agency feedback, and identifying critical information to be considered in a risk assessment-based weight of evidence determination of the need for rodent cancer bioassays. The reporting framework described herein was developed to support a chronic toxicity and carcinogenicity study waiver rationale, which includes information on use pattern(s), exposure scenario(s), pesticidal mode-of-action, physicochemical properties, metabolism, toxicokinetics, toxicological data including mechanistic data, and chemical read-across from similar registered pesticides. The framework could also be applied to endpoints other than chronic toxicity and carcinogenicity, and for chemicals other than agrochemicals.