The use and evaluation of primary data in 29 trichloroethylene carcinogen risk assessments

An analysis of the limitations and uncertainties of in vivo developmental neurotoxicity testing and assessment to identify the potential for alternative approaches

Limitations of regulatory in vivo developmental neurotoxicity (DNT) testing and assessment are well known, such as the 3Rs conflict, low throughput, high costs, high specific expertise needed and the lack of deeper mechanistic information. Moreover, the standard in vivo DNT data variability and in the experimental animal to human real life extrapolation is uncertain. Here, knowledge about these limitations and uncertainties is systematically summarized using a tabular OECD format. We also outline a hypothesis how alternative, fit-for-purpose Integrated Approaches to Testing and Assessment (IATAs) for DNT could improve current standard animal testing: Relative gains in 3Rs compliance, reduced costs, higher throughput, improved basic study design, higher standardization of testing and assessment and validation without 3Rs conflict, increasing the availability and reliability of DNT data. This could allow a more reliable comparative toxicity assessment over a larger proportion of chemicals within our global environment. The use of early, mechanistic, sensitive indicators for potential DNT could better support human safety assessment and mixture extrapolation. Using kinetic modelling ideally these could provide - eventually context dependent - at least the same level of human health protection. Such new approaches could also lead to a new mechanistic understanding for chemical safety, permitting determination of a dose that is likely not to trigger defined toxicity traits or pathways, rather than a dose not causing the current apical organism endpoints. The manuscript shall motivate and guide the development of new alternative methods for IATAs with diverse applications and support decision-making for their regulatory acceptance.

Perspectives on In Vitro to In Vivo Extrapolations

Quantitative in vitro to in vivo extrapolation (QIVIVE) is broadly considered a prerequisite bridge from in vitro findings to a dose paradigm. Quality and relevance of cell systems are the first prerequisite for QIVIVE. Information-rich and mechanistic endpoints (biomarkers) improve extrapolations, but a sophisticated endpoint does not make a bad cell model a good one. The next need is reverse toxicokinetics (TK), which estimates the dose necessary to reach a tissue concentration that is active in vitro. The Johns Hopkins Center for Alternatives to Animal Testing (CAAT) has created a roadmap for animal-free systemic toxicity testing, in which the needs and opportunities for TK are elaborated, in the context of different systemic toxicities. The report was discussed at two stakeholder forums in Brussels in 2012 and in Washington in 2013; the key recommendations are summarized herein. Contrary to common belief and the Paracelsus paradigm of everything is toxic, the majority of industrial chemicals do not exhibit toxicity. Strengthening the credibility of negative results of alternative approaches for hazard identification, therefore, avoids the need for QIVIVE. Here, especially the combination of methods in integrated testing strategies is most promising. Two further but very different approaches aim to overcome the problem of modeling in vivo complexity: The human-on-a-chip movement aims to reproduce large parts of living organism's complexity via microphysiological systems, that is, organ equivalents combined by microfluidics. At the same time, the Toxicity Testing in the 21st Century (Tox-21c) movement aims for mechanistic approaches (adverse outcome pathways as promoted by Organisation for Economic Co-operation and Development (OECD) or pathways of toxicity in the Human Toxome Project) for high-throughput screening, biological phenotyping, and ultimately a systems toxicology approach through integration with computer modeling. These 21st century approaches also require 21st century validation, for example, by evidence-based toxicology. Ultimately, QIVIVE is a prerequisite for extrapolating Tox-21c such approaches to human risk assessment.

An academic researcher's guide to increased impact on regulatory assessment of chemicals

The interactions between academic research and regulatory assessment of chemicals may in theory seem straightforward: researchers perform studies, and these studies are used by regulators for decision-making. However, in practice the situation is more complex, and many factors decide a research study's regulatory use. According to several EU chemical legislations, all available and relevant studies can be used in hazard and risk assessment of chemicals. However, in practice, standard tests conducted under GLP and sponsored and provided by industry are predominantly used. Peer-reviewed studies from independent sources are often disregarded or disputed since they often do not comply with regulatory data requirements and quality criteria. To help bridge such a gap, the aim of this paper is to give an overview of the general workings of legislation of chemicals and propose a set of actions to increase the usability of research data. In the end, this may increase the use of academic research for decision-making and ultimately result in more science-based policies. From a policy perspective, useful scientific evidence comprises those studies that are sufficiently reliable and relevant. This is not in contradiction to the aims of research and generally accepted scientific standards.

Evidence-based causation in toxicology

We introduced Evidence-based Toxicology (EBT) in 2005 to address the disparities that exist between the various Weight-of-Evidence (WOE) methods typically applied in the regulatory hazard decision-making arena and urged toxicologists to adopt the evidence-based guidelines long-utilized in medicine (i.e., Evidence-Based Medicine or EBM). This review of the activities leading to the adoption of evidence-based methods and EBT during the last decade demonstrates how fundamental concepts that form EBT, such as the use of systematic reviews to capture and consider all available information, are improving toxicological evaluations performed by various groups and agencies. We reiterate how the EBT framework, a process that provides a method for performing human chemical causation analyses in an objective, transparent and reproducible manner, differs significantly from past and current regulatory WOE approaches. We also discuss why the uncertainties associated with regulatory WOE schemes lead to a definition of the term “risk” that contains unquantifiable uncertainties not present in this term as it is used in epidemiology and medicine. We believe this distinctly different meaning of “risk” should be clearly conveyed to those not familiar with this difference (e.g., the lay public), when theoretical/nomologic risks associated with chemical-induced toxicities are presented outside of regulatory and related scientific parlance.

Models of science-policy interaction: exploring approaches to Bisphenol A management in the EU

This study investigated science-policy interaction models and their limitations under conditions of uncertainty. In detail, it looked at the management of the suspected endocrine-disrupting chemical Bisphenol A (BPA). Despite growing evidence that BPA is hazardous to human and environmental health, the level of scientific uncertainty is still high and, as a result, there is significant disagreement on the actual extent and type of risk. Analysis of decision-making processes at different regulatory levels (EU, Sweden, and the Swedish municipality of Gothenburg) exposed chemicals risk management and associated science-policy interaction under uncertainty. The results of the study show that chemicals management and associated science-policy interaction follow the modern model of science-policy interaction, where science is assumed to 'speak truth to policy' and highlights existing limitations of this model under conditions of uncertainty. The study not only explores alternative models (precautionary, consensus, science-policy demarcation. and extended participation) but also shows their limitations. The study concludes that all models come with their particular underlying assumptions, strengths, and limitations. At the same time, by exposing serious limitations of the modern model, the study calls for a rethinking of the relationship between science, policy, and management.

Qualichem in vivo: a tool for assessing the quality of in vivo studies and its application for bisphenol A

In regulatory toxicology, quality assessment of in vivo studies is a critical step for assessing chemical risks. It is crucial for preserving public health studies that are considered suitable for regulating chemicals are robust. Current procedures for conducting quality assessments in safety agencies are not structured, clear or consistent. This leaves room for criticism about lack of transparency, subjective influence and the potential for insufficient protection provided by resulting safety standards. We propose a tool called “Qualichem in vivo” that is designed to systematically and transparently assess the quality of in vivo studies used in chemical health risk assessment. We demonstrate its use here with 12 experts, using two controversial studies on Bisphenol A (BPA) that played an important role in BPA regulation in Europe. The results obtained with Qualichem contradict the quality assessments conducted by expert committees in safety agencies for both of these studies. Furthermore, they show that reliance on standardized guidelines to ensure scientific quality is only partially justified. Qualichem allows experts with different disciplinary backgrounds and professional experiences to express their individual and sometimes divergent views—an improvement over the current way of dealing with minority opinions. It provides a transparent framework for expressing an aggregated, multi-expert level of confidence in a study, and allows a simple graphical representation of how well the study integrates the best available scientific knowledge. Qualichem can be used to compare assessments of the same study by different health agencies, increasing transparency and trust in the work of expert committees. In addition, it may be used in systematic evaluation of in vivo studies submitted by industry in the dossiers that are required for compliance with the REACH Regulation. Qualichem provides a balanced, common framework for assessing the quality of studies that may or may not be following standardized guidelines.

In the shadow of the Cosmetic Directive--inconsistencies in EU environmental hazard classification requirements for UV-filters

UV-filters are chemicals with potentially environmental hazardous properties. In the European Union (EU), UV-filters contained in sunscreen products are currently regulated by the Cosmetic Directive (from July 2013 by the Cosmetic Products Regulation). Environmental hazard classifications according to the regulation on classification, labelling and packaging of substances and mixtures (CLP) must be determined for UV-filters contained in industrial chemical products, whereas UV-filters contained in sunscreens are exempted from CLP. In this study we determined the potential environmental hazard classifications of UV-filters and sunscreen products if the CLP regulation was to be required for cosmetic products. Two sunscreen products were evaluated in accordance with the aquatic environmental hazard criteria for mixtures. The results highlight that the inconsistencies in the current EU regulation of UV filters hamper the risk management of environmental hazards of UV filters used in cosmetic products. Almost 50% of the investigated UV-filters approved for use in cosmetic products on the European market according to the current Cosmetic Directive were identified to meet the CLP classification as being hazardous to the aquatic environment. Assuming a worst-case scenario, the two examined sunscreens could both be classified as hazardous to the aquatic environment with long-lasting effects according to CLP classification criteria. Hence, if the CLP regulation was applicable to sunscreen products, both brands could potentially be labelled with the environmental hazard pictogram and associated hazard and precautionary statements. Including cosmetic products, and thereby sunscreens, in the CLP regulation would contribute to a more harmonized and transparent regulation of potentially hazardous substances on the EU market.

Data and literature gathering in chemical cancer risk assessment

In recent years, chemical cancer risk assessment has faced major challenges: the demand for cancer risk assessment has grown considerably with strict legislation regarding chemical safety, whereas cancer hazard identification has turned increasingly complex due to the rapid development and high publication rate in biomedical sciences. Thus, much of the scientific evidence required for hazard identification is hidden in large collections of biomedical literature. Extensive guidelines have been produced to support cancer risk assessment under these circumstances. We evaluated whether these guidelines support the first, critical step of this task--data and literature gathering--and found that the guidance is vague. We propose ways to improve data and literature gathering for cancer risk assessment and suggest developing a computational literature search and analysis tool dedicated to the task. We describe the first prototype tool we have developed and discuss how it could help to improve the quality, consistency, and effectiveness of cancer risk assessment when developed further. Fully reliable automatic data and literature gathering may not be realistic; the retrieved articles will always need to be examined further by risk assessors. However, our proposal offers a starting point for improved data and literature gathering that can benefit the whole cancer risk assessment process.

The first step in the development of Text Mining technology for Cancer Risk Assessment: identifying and organizing scientific evidence in risk assessment literature

BACKGROUND

One of the most neglected areas of biomedical Text Mining (TM) is the development of systems based on carefully assessed user needs. We have recently investigated the user needs of an important task yet to be tackled by TM -- Cancer Risk Assessment (CRA). Here we take the first step towards the development of TM technology for the task: identifying and organizing the scientific evidence required for CRA in a taxonomy which is capable of supporting extensive data gathering from biomedical literature.

RESULTS

The taxonomy is based on expert annotation of 1297 abstracts downloaded from relevant PubMed journals. It classifies 1742 unique keywords found in the corpus to 48 classes which specify core evidence required for CRA. We report promising results with inter-annotator agreement tests and automatic classification of PubMed abstracts to taxonomy classes. A simple user test is also reported in a near real-world CRA scenario which demonstrates along with other evaluation that the resources we have built are well-defined, accurate, and applicable in practice.

CONCLUSION

We present our annotation guidelines and a tool which we have designed for expert annotation of PubMed abstracts. A corpus annotated for keywords and document relevance is also presented, along with the taxonomy which organizes the keywords into classes defining core evidence for CRA. As demonstrated by the evaluation, the materials we have constructed provide a good basis for classification of CRA literature along multiple dimensions. They can support current manual CRA as well as facilitate the development of an approach based on TM. We discuss extending the taxonomy further via manual and machine learning approaches and the subsequent steps required to develop TM technology for the needs of CRA.

Toward an evidence-based toxicology

The increasing demands on toxicology of large-scale risk assessment programmes for chemicals and emerging or expanding areas of chemical use suggest it is timely to review the toxicological toolbox. Like in clinical medicine, where an evidence-based medicine (EBM) is critically reviewing traditional approaches, toxicology has the opportunity to reshape and enlarge its methodology and approaches on the basis of compounded scientific knowledge. Such revision would have to be based on structured reviews of current practice, ie, assessment of test performance characteristics, mechanistic understanding, extended quality assurance, formal validation and the use of integrated testing strategies. This form of revision could optimize the balance between safety, costs and animal welfare, explicitly stating and, where possible, quantifying uncertainties. After a self-critical reassessment of current practices and evaluation of the thus generated information, such an evidence-based toxicology (EBT) promises to make better use of resources and to increase the quality of results, facilitating their interpretation. It shall open up hazard and also risk assessments to new technologies, flexibly accommodating current and future mechanistic understanding. An EBT will be better prepared to answer the continuously growing safety demands of modern societies.

What influences a health risk assessment?

In this paper it is claimed that the health risk assessment process is influenced by (at least) four general factors, namely: the regulatory framework, the quality and availability of scientific data, general risk assessment principles, and case-by-case assumptions. Furthermore, the scientific basis of risk assessment relies on three overall types of methods for data generation: standardized animal experiments, epidemiology, and non-standardized mechanism data. In this paper, the use of the different types of data for risk assessment purposes are analyzed in the light of the factors claimed to influence the risk assessment process. It is concluded that the availability of pre-defined criteria for the interpretation and evaluation of data for regulatory health risk assessment purposes need to be further developed. Especially with the implementation of the new European chemicals legislation REACH.

Principles and practices of health risk assessment under current EU regulations

Risk assessments serve as the foundation of regulatory decision-making on whether to take actions to reduce (or otherwise manage) a toxicological or ecotoxicological risk or not. To understand the complex process that leads from the generation of scientific data, via risk assessment to risk management decision-making, close studies of the scientific basis and risk assessment methods must be undertaken. This paper consists of two main parts. In the first part the principles of the European Union process for risk assessments, as defined by legislations and official guidelines, are briefly outlined. In the second part the actual workings of this system are exemplified by the results from case studies of the risk assessment processes for trichloroethylene and for acrylamide. The analysis and comparison of these two cases illustrates: (1) that generation of a large amount of data does not ensure consensus among risk assessors, (2) that controversy can regard different levels of detail, (3) that controversy can arise at different organizational and theoretical levels, (4) that risk assessments may be subject to (public) criticism even if the experts agree, and (5) that "scientific" controversies have a significant policy component.

A proposed methodology for selecting a trichloroethylene inhalation unit risk value for use in risk assessment

U.S. EPA's 2001 draft assessment of trichloroethylene (TCE) toxicity reviews the existing human and animal data on TCE carcinogenicity and proposes a 20-fold range of cancer potency values for use in risk assessment. Each value in the range is derived from a different source of data, either animal bioassays or epidemiology studies, and thus the range does not represent a distribution which can be characterized by statistical parameters such as a mean or 95% confidence interval. The U.S. EPA suggests users choose a single slope factor from among those it describes as appropriate for the population of interest and mode of exposure, but little guidance is given for making this choice. We propose an approach for determining the most scientifically defensible carcinogenic inhalation unit risk estimate from the range of slope factors developed by U.S. EPA, one that relies on accepted principles for evaluating scientific studies. Based on these considerations, we identify the most appropriate interim unit risk for low-level inhalation exposure as 9 x 10(-7) per microg/m(3). This approach may have fairly broad utility if U.S. EPA elects to use a similar approach in future assessments of other chemicals.

VHL mutations in renal cell cancer: does occupational exposure to trichloroethylene make a difference?

Occupational exposures have long been suspected to play a role in the incidence of renal cell carcinoma (RCC). Especially, the carcinogenicity of the industrial solvent trichloroethylene (TCE) has been controversially debated, both with respect to the epidemiological and the molecular studies. In order to further elucidate this issue, it appeared important to compare suitable RCC patient groups, i.e., TCE-exposed versus non-TCE-exposed patients. We evaluated RCC from a previous German study that had described differences in RCC risks between TCE-exposed (n=17) and non-exposed patients (n=21). We compared age at diagnosis and histopathologic parameters of tumors as well as somatic mutation characteristics in the kidney cancer causing VHL tumor suppressor gene. RCC did not differ with respect to histopathological characteristics in both patient groups. We noticed a younger age at diagnosis in TCE-exposed patients compared to non-exposed patients (P=0.01). Moreover, the non-TCE-exposed patients did not share the somatic VHL mutation characteristics of TCE-exposed patients such as the previously identified hot spot mutation 454 C > T P81S or multiple mutations. These data support the notion of a putative genotoxic effect of TCE leading to VHL gene damage and subsequent occurrence of RCC in highly exposed subjects.

Acrylamide and cancer risk—expert risk assessments and the public debate

This study has two parts. In the first part, fourteen carcinogen risk assessments of acrylamide made by different expert groups during the years 1976-2002 are compared in terms of their overall conclusions and their use of primary data. In the second part, the public debate on acrylamide and cancer risks and the questioning of the expert risk assessment, that arose as a reaction to the identification of this substance in staple food is discussed. In the first part it is shown that the expert risk assessors concur to a large degree about the assessment of the acrylamide potential to cause cancer. Three risk assessors have concluded that acrylamide is neither carcinogenic to humans nor to animals, while eleven risk assessors have concluded that acrylamide is carcinogenic in animals and is likely to be carcinogenic in humans. The differences in the overall conclusions seem to a large extent be explained by an evolving database. The risk assessors agree considerably on how to interpret and evaluate the available primary data, but the coverage of the available references is low. These results are also compared to those previously published on risk assessments of trichloroethylene. In the second part the arguments used in the public debate to question the expert risk assessment are summarized and it is argued that they are not based on the principles generally accepted in toxicological risk assessment.

Indicators of uncertainty in chemical risk assessments

For most of the chemical substances that are subject to regulatory and industrial decision making, important toxicological data are missing. The available dataset is often difficult to interpret, and the differences between alternative, scientifically reasonable interpretations may have major impact on decision making. Since such uncertainties are an important factor in decision making it is essential that they be reported in a transparent and understandable way. In order to clarify how toxicologists report uncertainties, 30 risk assessments for one and the same substance (trichloroethylene) from the years 1973-2001 were searched for phrases indicating uncertainty. These phrases can be divided between four categories: contentual, epistemic, conditionalising, and inferential uncertainty indicators. A typology of uncertainty indicators, based on these categories, is proposed. It is concluded that the use of uncertainty indicators in these texts is not transparent and that the development of standardised uncertainty indicators should significantly improve communications both within the scientific community and between scientists and policymakers.

Scrutinizing ACGIH risk assessments: the trichloroethylene case

BACKGROUND

The American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit values (TLVs) for occupational exposure to chemicals and physical agents have been very influential in the setting of occupational exposure limits in many countries.

METHODS

Three ACGIH risk assessments of the chlorinated solvent trichloroethylene (TCE) [ACGIH (1989): 5th edition; ACGIH (1992): 5th edition. Revised Vol II; ACGIH (1996): Suppl. 6th edition] are compared to 26 other risk assessments made of the same chemical substance. The documents are compared in terms of their overall conclusions and the data selected for assessment.

RESULTS

It is shown that these ACGIH risk assessment documents were based on incomplete and biased data sets.

CONCLUSIONS

The data on which the ACGIH [ACGIH (1996): Suppl. 6th edition] base their TCE risk assessment do not adequately reflect the available scientific knowledge about TCE toxicity and carcinogenicity. This may have influenced their conclusion that TCE is not carcinogenic in either animals or humans which stand out compared to contemporary risk assessments.

Science and transscience in carcinogen risk assessment--the European Union regulatory process for trichloroethylene

This is a study of carcinogen risk assessment of the chlorinated solvent trichloroethylene within the European Union existing substances program and the classification and labeling process. The focus is on the most active and influential participants of this process, namely, those from the United Kingdom, Germany, and Sweden, and from industry. The member state and other experts have different opinions regarding the appropriate classification of trichloroethylene for mutagenicity (no classification or category 3) and carcinogenicity (category 3, 2, or 1). In this article these differences are described, as well as how the primary carcinogenicity and mutagenicity data have been interpreted and evaluated by these participants. It is concluded that underlying the different assessments are disagreements about issues that to some degree lie outside the scope of purely scientific considerations.

Trace level determination of trichloroethylene from liver, lung and kidney tissues by gas chromatography-magnetic sector mass spectrometry

Trichloroethylene (TCE) is a common industrial chemical that has been heavily used as a metal degreaser and a solvent for the past 100 years. As a result of the extensive use and production of this compound, it has become prevalent in the environment, appearing at over 50% of the hazardous waste sites on the US EPA's National Priorities List (NPL). TCE exposure has been linked to neurological dysfunction as well as to several types of cancer in animals. This paper describes the development and validation of a gas chromatography-mass spectrometry (GC-MS) method for the quantitation of trace levels of TCE in its target tissues (i.e. liver, kidney and lungs). The limit of quantitation (5 ng/ml) is substantially lower than currently published methods for the analysis of TCE in tissues. The % RSD and % Error for the assay falls within the acceptable range (<15% for middle and high QC points and <20% for low QC points), and the recovery is high from all tissues (>79%).

Scrutinizing three trichloroethylene carcinogenicity classifications in the European Union--implications for the risk assessment process

In this paper, carcinogenicity classifications of the chlorinated solvent trichloroethylene (TCE) made by the European Union Commission Expert Groups in 1976, 1988, and 2001 are scrutinized and alternative classifications are proposed. It is argued that the TCE database at these three points in time could have been interpreted to fulfill the criteria for stricter classifications than those actually made. Implications of this for the classification process are discussed.

The use of mechanistic data and the handling of scientific uncertainty in carcinogen risk assessments. The trichloroethylene example

The purpose of this paper is to explore how risk assessors actually use mechanistic data in carcinogen risk assessment and to discuss how the handling of scientific uncertainty may affect the outcome of the risk assessment. The analysis is performed by comparing 29 trichloroethylene risk assessment documents in general and 2 of these, namely the ECETOC (1994, Trichloroethylene: Assessment of Human Carcinogenic Hazard, Technical Report No. 60) and the OECD/EU (1996, Initial Assessment Report for the 4th SIAM (Screening Information Data Set Initial Assessment Meeting), May 1996: Trichloroethylene, sponsor country, United Kingdom [Draft]), in more detail. It is concluded that in this example the ECETOC required less evidence for considering a carcinogenic mechanism irrelevant to humans than did the OECD/EU risk assessors. There are examples of when two risk assessors have selected different primary data for their argumentation and also examples of how one and the same primary publication was interpreted differently. Biased data selection and evaluation of primary data that correlate to the risk assessor's overall conclusions have also been identified. The general comparison of all 29 TCE risk assessment documents indicates that the assessment of scientific uncertainty in the mechanistic data affects the overall conclusions.

Interpretations of primary carcinogenicity data in 29 trichloroethylene risk assessments

This paper explores to what extent interpretations of individual primary carcinogenicity data differ between different risk assessors, and discusses possible reasons for such differences as well as their impact on the overall risk assessment conclusions. For this purpose 29 different TCE carcinogenicity risk assessments are used as examples. It is concluded that the TCE risk assessors surprisingly often interpret and evaluate primary data differently. Two particular reasons for differences in data interpretation are discussed: different assessments of statistics, and different assessments of whether the results obtained in bioassays have toxicological relevance. Differences in the interpretation and evaluation of epidemiological data are also explored and discussed.