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The long running controversy about the relative merits of hazard-based versus risk-based approaches has been investigated. There are three levels of hazard codification: level 1 divides chemicals into dichotomous bands of hazardous and non-hazardous; level 2 divides chemicals into bands of hazard based on severity and/or potency; and level 3 places each chemical on a continuum of hazard based on severity and/or potency. Any system which imposes compartments onto a continuum will give rise to issues at the boundaries, especially with only two compartments. Level 1 schemes are only justifiable if there is no variation in severity, or potency or if there is no threshold. This is the assumption implicit in GHS/EU classification for carcinogenicity, reproductive toxicity and mutagenicity. However, this assumption has been challenged. Codification level 2 hazard assessments offer a range of choices and reduce the built-in conflict inherent in the level 1 process. Level 3 assessments allow a full range of choices between the extremes and reduce the built-in conflict even more. The underlying reason for the controversy between hazard and risk is the use of level 1 hazard codification schemes in situations where there are ranges of severity and potency which require the use of level 2 or level 3 hazard codification. There is not a major difference between level 2 and level 3 codification, and they can both be used to select appropriate risk management options. Existing level 1 codification schemes should be reviewed and developed into level 2 schemes where appropriate.

Several exposure limits for perchlorate have been developed based on an early key event, inhibition of radioactive iodide uptake (RAIU) by the thyroid. These assessments have used a variety of definitions of the point of departure. The current assessment revisited the modeling for inhibition of RAIU, using state of the science methods. Bayesian hierarchical modeling was used to account for the repeated measures on the same individuals in the key dataset, and the underlying Beta distribution used for the modeling correctly reflected the bounding of RAIU between 0 and 1. We defined the BMR as a point value of 8% RAIU (rather than a change in RAIU), based on descriptions in the medical literature that RAIU below this value is considered abnormal. Because a definition of the BMR based on the mean response would correspond to about 50% of the population with a response below the BMR at the benchmark dose, we used a hybrid definition of the BMR. That is, the BMD was defined as the dose at which it was estimated that there would be a 10% extra risk in the population of having RAIU of 8% or lower. The resulting point of departure based on the BMDL was 0.03 mg/kg-day.

Cancer remains the second most frequent cause of death in human populations worldwide, which has been reflected in the emphasis placed on management of risk from environmental chemicals considered to be potential human carcinogens. The formation of DNA adducts has been considered as one of the key events of cancer, and persistence and/or failure of repair of these adducts may lead to mutation, thus initiating cancer. Some chemical carcinogens can produce DNA adducts, and DNA adducts have been used as biomarkers of exposure. However, DNA adducts of various types are also produced endogenously in the course of normal metabolism. Since both endogenous physiological processes and exogenous exposure to xenobiotics can cause DNA adducts, the differentiation of the sources of DNA adducts can be highly informative for cancer risk assessment. This review summarizes a highly applicable methodology, termed stable isotope labeling and mass spectrometry (SILMS), that is superior to previous methods, as it not only provides absolute quantitation of DNA adducts but also differentiates the exogenous and endogenous origins of DNA adducts. SILMS uses stable isotope-labeled substances for exposure, followed by DNA adduct measurement with highly sensitive mass spectrometry. Herein, the utilities and advantage of SILMS have been demonstrated by the rich data sets generated over the last two decades in improving the risk assessment of chemicals with DNA adducts being induced by both endogenous and exogenous sources, such as formaldehyde, vinyl acetate, vinyl chloride, and ethylene oxide.

Developments in the understanding of the etiology of cancer have profound implications for the way the carcinogenicity of chemicals is addressed. This paper proposes a unified theory of carcinogenesis that will illuminate better ways to evaluate and regulate chemicals. In the last four decades, we have come to understand that for a cell and a group of cells to begin the process of unrestrained growth that is defined as cancer, there must be changes in DNA that reprogram the cell from normal to abnormal. Cancer is the consequence of DNA coding errors that arise either directly from mutagenic events or indirectly from cell proliferation especially if sustained. Chemicals that act via direct interaction with DNA can induce cancer because they cause mutations which can be carried forward in dividing cells. Chemicals that act via non-genotoxic mechanisms must be dosed to maintain a proliferative environment so that the steps toward neoplasia have time to occur. Chemicals that induce increased cellular proliferation can be divided into two categories: those which act by a cellular receptor to induce cellular proliferation, and those which act via non-specific mechanisms such as cytotoxicity. This knowledge has implications for testing chemicals for carcinogenic potential and risk management.

Over 50 years, we have learned a great deal about the biology that underpins cancer but our approach to testing chemicals for carcinogenic potential has not kept up. Only a small number of chemicals has been tested in animal-intensive, time consuming, and expensive long-term bioassays in rodents. We now recommend a transition from the bioassay to a decision-tree matrix that can be applied to a broader range of chemicals, with better predictivity, based on the premise that cancer is the consequence of DNA coding errors that arise either directly from mutagenic events or indirectly from sustained cell proliferation. The first step is in silico and in vitro assessment for mutagenic (DNA reactive) activity. If mutagenic, it is assumed to be carcinogenic unless evidence indicates otherwise. If the chemical does not show mutagenic potential, the next step is assessment of potential human exposure compared to the threshold for toxicological concern (TTC). If potential human exposure exceeds the TTC, then testing is done to look for effects associated with the key characteristics that are precursors to the carcinogenic process, such as increased cell proliferation, immunosuppression, or significant estrogenic activity. Protection of human health is achieved by limiting exposures to below NOEALs for these precursor effects. The decision tree matrix is animal-sparing, cost effective, and in step with our growing knowledge of the process of cancer formation.

The evolved World Health Organization/International Programme on Chemical Safety mode of action (MOA) framework provides a structure for evaluating evidence in pathways of causally linked key events (KE) leading to adverse health effects. Although employed globally, variability in use of the MOA framework has led to different interpretations of the sufficiency of evidence in support of hypothesized MOAs. A proof of concept extension of the MOA framework is proposed for scoring confidence in the supporting data to improve scientific justification for MOA use in characterizing hazards and selecting dose-response extrapolation methods for specific chemicals. This involves selecting hypothesized MOAs, and then, for each MOA, scoring the weight of evidence (WOE) in support of causality for each KE using evolved Bradford Hill causal considerations (biological plausibility, essentiality, dose-response concordance, consistency, and analogy). This early proof of concept method is demonstrated by comparing two potential MOAs (mutagenicity and peroxisome proliferator activated receptor-alpha) for clofibrate, a rodent liver carcinogen. Quantitative confidence scoring of hypothesized MOAs is shown to be useful in characterizing the likely operative MOA. To guide method refinement and future confidence scoring for a spectrum of MOAs, areas warranting further focus and lessons learned, including the need to incorporate a narrative discussion of the weights used in the evaluation and an overall evaluation of the plausibility of the outcome, are presented.

The Organization for Economic Cooperation and Development (OECD) recently revised the test guidelines (TGs) for genetic toxicology. This article describes the main issues addressed during the revision process, and the new and consistent recommendations made in the revised TGs for: (1) demonstration of laboratory proficiency; (2) generation and use of robust historical control data; (3) improvement of the statistical power of the tests; (4) selection of top concentration for in vitro assays; (5) consistent data interpretation and determination of whether the result is clearly positive, clearly negative or needs closer consideration; and, (6) consideration of 3R's for in vivo assay design. The revision process resulted in improved consistency among OECD TGs (including the newly developed ones) and more comprehensive recommendations for the conduct and the interpretation of the assays. Altogether, the recommendations made during the revision process should improve the efficiency, by which the data are generated, and the quality and reliability of test results. Environ. Mol. Mutagen. 58:284-295, 2017. © 2017 Wiley Periodicals, Inc.

The International Workshop on Genotoxicity Testing (IWGT) meets every four years to obtain consensus on unresolved issues associated with genotoxicity testing. At the 2017 IWGT meeting in Tokyo, four sub-groups addressed issues associated with the Organization for Economic Cooperation and Development (OECD) Test Guideline TG471, which describes the use of bacterial reverse-mutation tests. The strains sub-group analyzed test data from >10,000 chemicals, tested additional chemicals, and concluded that some strains listed in TG471 are unnecessary because they detected fewer mutagens than other strains that the guideline describes as equivalent. Thus, they concluded that a smaller panel of strains would suffice to detect most mutagens. The laboratory proficiency sub-group recommended (a) establishing strain cell banks, (b) developing bacterial growth protocols that optimize assay sensitivity, and (c) testing "proficiency compounds" to gain assay experience and establish historical positive and control databases. The sub-group on criteria for assay evaluation recommended that laboratories (a) track positive and negative control data; (b) develop acceptability criteria for positive and negative controls; (c) optimize dose-spacing and the number of analyzable doses when there is evidence of toxicity; (d) use a combination of three criteria to evaluate results: a dose-related increase in revertants, a clear increase in revertants in at least one dose relative to the concurrent negative control, and at least one dose that produced an increase in revertants above control limits established by the laboratory from historical negative controls; and (e) establish experimental designs to resolve unclear results. The in silico sub-group summarized in silico utility as a tool in genotoxicity assessment but made no specific recommendations for TG471. Thus, the workgroup identified issues that could be addressed if TG471 is revised. The companion papers (a) provide evidence-based approaches, (b) recommend priorities, and (c) give examples of clearly defined terms to support revision of TG471.

Developments in the understanding of the etiology of cancer have undermined the 1970s concept that chemicals are either "carcinogens" or "non-carcinogens". The capacity to induce cancer should not be classified in an inflexible binary manner as present (carcinogen) or absent (non-carcinogen). Chemicals may induce cancer by three categories of mode of action: direct interaction with DNA or DNA replication including DNA repair and epigenetics; receptor-mediated induction of cell division; and non-specific induction of cell division. The long-term rodent bioassay is neither appropriate nor efficient to evaluate carcinogenic potential for humans and to inform risk management decisions. It is of questionable predicitiveness, expensive, time consuming, and uses hundreds of animals. Although it has been embedded in practice for over 50 years, it has only been used to evaluate less than 5% of chemicals that are in use. Furthermore, it is not reproducible because of the probabilisitic nature of the process it is evaluating combined with dose limiting toxicity, dose selection, and study design. The modes of action that lead to the induction of tumors are already considered under other hazardous property categories in classification (Mutagenicity/Genotoxicity and Target Organ Toxicity); a separate category for Carcinogenicity is not required and provides no additional public health protection.

This report summarizes the discussion, conclusions, and points of consensus of the IWGT Working Group on Quantitative Approaches to Genetic Toxicology Risk Assessment (QWG) based on a meeting in Foz do Iguacu, Brazil October 31–November 2, 2013. Topics addressed included (1) the need for quantitative dose–response analysis, (2) methods to analyze exposure–response relationships & derive point of departure (PoD) metrics, (3) points of departure (PoD) and mechanistic threshold considerations, (4) approaches to define exposure-related risks, (5) empirical relationships between genetic damage (mutation) and cancer, and (6) extrapolations across test systems and species. This report discusses the first three of these topics and a companion report discusses the latter three. The working group critically examined methods for determining point of departure metrics (PoDs) that could be used to estimate low-dose risk of genetic damage and from which extrapolation to acceptable exposure levels could be made using appropriate mode of action information and uncertainty factors. These included benchmark doses (BMDs) derived from fitting families of exponential models, the N o O bserved G enotoxic E ffect L evel (NOGEL), and “threshold” or breakpoint dose (BPD) levels derived from bilinear models when mechanistic data supported this approach. The QWG recognizes that scientific evidence suggests that thresholds below which genotoxic effects do not occur likely exist for both DNA-reactive and DNA-nonreactive substances, but notes that small increments of the spontaneous level cannot be unequivocally excluded either by experimental measurement or by mathematical modeling. Therefore, rather than debating the theoretical possibility of such low-dose effects, emphasis should be placed on determination of PoDs from which acceptable exposure levels can be determined by extrapolation using available mechanistic information and appropriate uncertainty factors. This approach places the focus on minimization of the genotoxic risk, which protects against the risk of the development of diseases resulting from the genetic damage. Based on analysis of the strengths and weaknesses of each method, the QWG concluded that the order of preference of PoD metrics is the statistical lower bound on the BMD > the NOGEL > a statistical lower bound on the BPD. A companion report discusses the use of these metrics in genotoxicity risk assessment, including scaling and uncertainty factors to be considered when extrapolating below the PoD and/or across test systems and to the human.

The NRC report Science and Decisions: Advancing Risk Assessment made several recommendations to improve chemical risk assessment, with a focus on in-depth chronic dose–response assessments conducted by the U.S. Environmental Protection Agency. The recommendations addressed two broad elements: improving technical analysis and utility for decision making. To advance the discussions in the NRC report, in three multi-stakeholder workshops organized by the Alliance for Risk Assessment, available and evolving risk assessment methodologies were considered through the development and application of case studies. A key product was a framework ( http://www.allianceforrisk.org/Workshop/Framework/ProblemFormulation.html ) to guide risk assessors and managers to various dose–response assessment methods relevant to a range of decision contexts ranging from priority setting to full assessment, as illustrated by case studies. It is designed to facilitate selection of appropriate methodology for a variety of problem formulations and includes a variety of methods with supporting case studies, for areas flagged specifically by the NRC committee for consideration – e.g., susceptible sub-populations, population variability and background. The framewok contributes to organization and communication about methodologies for incorporating increasingly biologically informed and chemical specific knowledge into dose–response analysis, which is considered critical in evolving fit-for-purpose assessment to address relevant problem formulations.

Background: Biomonitoring data reported in the National Report on Human Exposure to Environmental Chemicals [NER; Centers for Disease Control and Prevention (2012)] provide information on the presence and concentrations of > 400 chemicals in human blood and urine. Biomonitoring Equivalents (BEs) and other risk assessment–based values now allow interpretation of these biomonitoring data in a public health risk context. Objectives: We compared the measured biomarker concentrations in the NER with BEs and similar risk assessment values to provide an across-chemical risk assessment perspective on the measured levels for approximately 130 analytes in the NER. Methods: We identified available risk assessment–based biomarker screening values, including BEs and Human Biomonitoring-I (HBM-I) values from the German Human Biomonitoring Commission. Geometric mean and 95th percentile population biomarker concentrations from the NER were compared to the available screening values to generate chemical-specific hazard quotients (HQs) or cancer risk estimates. Conclusions: Most analytes in the NER show HQ values of < 1; however, some (including acrylamide, dioxin-like chemicals, benzene, xylene, several metals, di-2(ethylhexyl)phthalate, and some legacy organochlorine pesticides) approach or exceed HQ values of 1 or cancer risks of > 1 × 10–4 at the geometric mean or 95th percentile, suggesting exposure levels may exceed published human health benchmarks. This analysis provides for the first time a means for examining population biomonitoring data for multiple environmental chemicals in the context of the risk assessments for those chemicals. The results of these comparisons can be used to focus more detailed chemical-specific examination of the data and inform priorities for chemical risk management and research.

The Organization for Economic Cooperation and Development (OECD) recently revised the test guidelines (TGs) for genetic toxicology. This article describes the main issues addressed during the revision process, and the new and consistent recommendations made in the revised TGs for: (1) demonstration of laboratory proficiency; (2) generation and use of robust historical control data; (3) improvement of the statistical power of the tests; (4) selection of top concentration for in vitro assays; (5) consistent data interpretation and determination of whether the result is clearly positive, clearly negative or needs closer consideration; and, (6) consideration of 3R's for in vivo assay design. The revision process resulted in improved consistency among OECD TGs (including the newly developed ones) and more comprehensive recommendations for the conduct and the interpretation of the assays. Altogether, the recommendations made during the revision process should improve the efficiency, by which the data are generated, and the quality and reliability of test results. Environ. Mol. Mutagen. 58:284-295, 2017. © 2017 Wiley Periodicals, Inc.

The HESI-led RISK21 effort has developed a framework supporting the use of twenty-first century technology in obtaining and using information for chemical risk assessment. This framework represents a problem formulation-based, exposure-driven, tiered data acquisition approach that leads to an informed decision on human health safety to be made when sufficient evidence is available. It provides a transparent and consistent approach to evaluate information in order to maximize the ability of assessments to inform decisions and to optimize the use of resources. To demonstrate the application of the framework’s roadmap and matrix, this case study evaluates a large number of chemicals that could be present in drinking water. The focus is to prioritize which of these should be considered for human health risk as individual contaminants. The example evaluates 20 potential drinking water contaminants, using the tiered RISK21 approach in combination with graphical representation of information at each step, using the RISK21 matrix. Utilizing the framework, 11 of the 20 chemicals were assigned low priority based on available exposure data alone, which demonstrated that exposure was extremely low. The remaining nine chemicals were further evaluated, using refined estimates of toxicity based on readily available data, with three deemed high priority for further evaluation. In the present case study, it was determined that the greatest value of additional information would be from improved exposure models and not from additional hazard characterization.

Classification schemes for carcinogenicity based solely on hazard-identification such as the IARC monograph process and the UN system adopted in the EU have become outmoded. They are based on a concept developed in the 1970s that chemicals could be divided into two classes: carcinogens and non-carcinogens. Categorization in this way places into the same category chemicals and agents with widely differing potencies and modes of action. This is how eating processed meat can fall into the same category as sulfur mustard gas. Approaches based on hazard and risk characterization present an integrated and balanced picture of hazard, dose response and exposure and allow informed risk management decisions to be taken. Because a risk-based decision framework fully considers hazard in the context of dose, potency, and exposure the unintended downsides of a hazard only approach are avoided, e.g., health scares, unnecessary economic costs, loss of beneficial products, adoption of strategies with greater health costs, and the diversion of public funds into unnecessary research. An initiative to agree upon a standardized, internationally acceptable methodology for carcinogen assessment is needed now. The approach should incorporate principles and concepts of existing international consensus-based frameworks including the WHO IPCS mode of action framework.

Background: Methylmercury (MeHg) is a known neuro-toxicant. Emerging evidence indicates it may have adverse effects on the neuro-logic and other body systems at common low levels of exposure. Impacts of MeHg exposure could vary by individual susceptibility or be confounded by bene-ficial nutrients in fish containing MeHg. Despite its global relevance, synthesis of the available literature on low-level MeHg exposure has been limited. Objectives: We undertook a synthesis of the current knowledge on the human health effects of low-level MeHg exposure to provide a basis for future research efforts, risk assessment, and exposure remediation policies worldwide. Data sources and extraction: We reviewed the published literature for original human epidemio-logic research articles that reported a direct biomarker of mercury exposure. To focus on high-quality studies and those specifically on low mercury exposure, we excluded case series, as well as studies of populations with unusually high fish consumption (e.g., the Seychelles), marine mammal consumption (e.g., the Faroe Islands, circumpolar, and other indigenous populations), or consumption of highly contaminated fish (e.g., gold-mining regions in the Amazon). Data synthesis: Recent evidence raises the possibility of effects of low-level MeHg exposure on fetal growth among susceptible subgroups and on infant growth in the first 2 years of life. Low-level effects of MeHg on neuro-logic outcomes may differ by age, sex, and timing of exposure. No clear pattern has been observed for cardio-vascular disease (CVD) risk across populations or for specific CVD end points. For the few studies evaluating immunologic effects associated with MeHg, results have been inconsistent. Conclusions: Studies targeted at identifying potential mechanisms of low-level MeHg effects and characterizing individual susceptibility, sexual dimorphism, and non-linearity in dose response would help guide future prevention, policy, and regulatory efforts surrounding MeHg exposure.

Fish and shellfish are widely available foods that provide important nutrients, particularly n-3 polyunsaturated fatty acids (n-3 PUFAs), to many populations globally. These nutrients, especially docosahexaenoic acid, confer benefits to brain and visual system development in infants and reduce risks of certain forms of heart disease in adults. However, fish and shellfish can also be a major source of methylmercury (MeHg), a known neurotoxicant that is particularly harmful to fetal brain development. This review documents the latest knowledge on the risks and benefits of seafood consumption for perinatal development of infants. It is possible to choose fish species that are both high in n-3 PUFAs and low in MeHg. A framework for providing dietary advice for women of childbearing age on how to maximize the dietary intake of n-3 PUFAs while minimizing MeHg exposures is suggested.

Disinfection by-products (DBPs) are formed when disinfectants (chlorine, ozone, chlorine dioxide, or chloramines) react with naturally occurring organic matter, anthropogenic contaminants, bromide, and iodide during the production of drinking water. Here we review 30 years of research on the occurrence, genotoxicity, and carcinogenicity of 85 DBPs, 11 of which are currently regulated by the U.S., and 74 of which are considered emerging DBPs due to their moderate occurrence levels and/or toxicological properties. These 74 include halonitromethanes, iodo-acids and other unregulated halo-acids, iodo-trihalomethanes (THMs), and other unregulated halomethanes, halofuranones (MX [3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone] and brominated MX DBPs), haloamides, haloacetonitriles, tribromopyrrole, aldehydes, and N-nitrosodimethylamine (NDMA) and other nitrosamines. Alternative disinfection practices result in drinking water from which extracted organic material is less mutagenic than extracts of chlorinated water. However, the levels of many emerging DBPs are increased by alternative disinfectants (primarily ozone or chloramines) compared to chlorination, and many emerging DBPs are more genotoxic than some of the regulated DBPs. Our analysis identified three categories of DBPs of particular interest. Category 1 contains eight DBPs with some or all of the toxicologic characteristics of human carcinogens: four regulated (bromodichloromethane, dichloroacetic acid, dibromoacetic acid, and bromate) and four unregulated DBPs (formaldehyde, acetaldehyde, MX, and NDMA). Categories 2 and 3 contain 43 emerging DBPs that are present at moderate levels (sub- to low-mug/L): category 2 contains 29 of these that are genotoxic (including chloral hydrate and chloroacetaldehyde, which are also a rodent carcinogens); category 3 contains the remaining 14 for which little or no toxicological data are available. In general, the brominated DBPs are both more genotoxic and carcinogenic than are chlorinated compounds, and iodinated DBPs were the most genotoxic of all but have not been tested for carcinogenicity. There were toxicological data gaps for even some of the 11 regulated DBPs, as well as for most of the 74 emerging DBPs. A systematic assessment of DBPs for genotoxicity has been performed for approximately 60 DBPs for DNA damage in mammalian cells and 16 for mutagenicity in Salmonella. A recent epidemiologic study found that much of the risk for bladder cancer associated with drinking water was associated with three factors: THM levels, showering/bathing/swimming (i.e., dermal/inhalation exposure), and genotype (having the GSTT1-1 gene). This finding, along with mechanistic studies, highlights the emerging importance of dermal/inhalation exposure to the THMs, or possibly other DBPs, and the role of genotype for risk for drinking-water-associated bladder cancer. More than 50% of the total organic halogen (TOX) formed by chlorination and more than 50% of the assimilable organic carbon (AOC) formed by ozonation has not been identified chemically. The potential interactions among the 600 identified DBPs in the complex mixture of drinking water to which we are exposed by various routes is not reflected in any of the toxicology studies of individual DBPs. The categories of DBPs described here, the identified data gaps, and the emerging role of dermal/inhalation exposure provide guidance for drinking water and public health research.

Copper (Cu) and its alloys are used extensively in domestic and industrial applications. Cu is also an essential element in mammalian nutrition. Since both copper deficiency and copper excess produce adverse health effects, the dose-response curve is U-shaped, although the precise form has not yet been well characterized. Many animal and human studies were conducted on copper to provide a rich database from which data suitable for modeling the dose-response relationship for copper may be extracted. Possible dose-response modeling strategies are considered in this review, including those based on the benchmark dose and categorical regression. The usefulness of biologically based dose-response modeling techniques in understanding copper toxicity was difficult to assess at this time since the mechanisms underlying copper-induced toxicity have yet to be fully elucidated. A dose-response modeling strategy for copper toxicity was proposed associated with both deficiency and excess. This modeling strategy was applied to multiple studies of copper-induced toxicity, standardized with respect to severity of adverse health outcomes and selected on the basis of criteria reflecting the quality and relevance of individual studies. The use of a comprehensive database on copper-induced toxicity is essential for dose-response modeling since there is insufficient information in any single study to adequately characterize copper dose-response relationships. The dose-response modeling strategy envisioned here is designed to determine whether the existing toxicity data for copper excess or deficiency may be effectively utilized in defining the limits of the homeostatic range in humans and other species. By considering alternative techniques for determining a point of departure and low-dose extrapolation (including categorical regression, the benchmark dose, and identification of observed no-effect levels) this strategy will identify which techniques are most suitable for this purpose. This analysis also serves to identify areas in which additional data are needed to better define the characteristics of dose-response relationships for copper-induced toxicity in relation to excess or deficiency.

The use of assumptions is a part of all human conceptual thinking, as is the use of standard thought procedures that become default approaches. In most discourse, assumptions and defaults are uncon...

a Novartis Institutes for BioMedical Research, Preclinical Safety, 4002 Basel, Switzerland b Public Interest Incorporated Foundation BioSafety Research Center, Iwata, Japan c National Institute of Health Sciences, Division of Genetics & Mutagenesis, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan d Federal Institute for Drugs and Medical Devices (BfArM), Bonn, Germany e Exponent, Inc., Center for Toxicology & Mechanistic Biology, Midland, MI 48640, USA f Pharmaceutical Sciences, Roche Innovation Center, F Hoffmann-La Roche AG, CH 4070 Basel, Switzerland g Office of Science Policy, Office of Research and Development, U.S. Environmental Protection Agency, Room 51134 RRB, 1200 Pennsylvania Avenue NW (8104R), Washington DC 20460-0001, USA h Safety Research Laboratories, Mitsubishi Tanabe Pharma Co., Chiba 292-0818, Japan i Kirkland Consulting, PO Box 79, Tadcaster LS24 0AS, UK

This is the second of two reports from the International Workshops on Genotoxicity Testing (IWGT) Working Group on Quantitative Approaches to Genetic Toxicology Risk Assessment (the QWG). The first report summarized the discussions and recommendations of the QWG related to the need for quantitative dose–response analysis of genetic toxicology data, the existence and appropriate evaluation of threshold responses, and methods to analyze exposure-response relationships and derive points of departure (PoDs) from which acceptable exposure levels could be determined. This report summarizes the QWG discussions and recommendations regarding appropriate approaches to evaluate exposure-related risks of genotoxic damage, including extrapolation below identified PoDs and across test systems and species. Recommendations include the selection of appropriate genetic endpoints and target tissues, uncertainty factors and extrapolation methods to be considered, the importance and use of information on mode of action, toxicokinetics, metabolism, and exposure biomarkers when using quantitative exposure-response data to determine acceptable exposure levels in human populations or to assess the risk associated with known or anticipated exposures. The empirical relationship between genetic damage (mutation and chromosomal aberration) and cancer in animal models was also examined. It was concluded that there is a general correlation between cancer induction and mutagenic and/or clastogenic damage for agents thought to act via a genotoxic mechanism, but that the correlation is limited due to an inadequate number of cases in which mutation and cancer can be compared at a sufficient number of doses in the same target tissues of the same species and strain exposed under directly comparable routes and experimental protocols.

There are several pieces of legislation based on human health assessment that set the framework for U.S. EPA's regulation of water contaminants, such as bromate. The Safe Drinking Water Act, for example, specifies that the best available science be used in support of regulation of drinking water contaminants, and highlights that regulations must provide protection to sensitive human populations. Recent EPA guidance, including the 2005 Cancer Guidelines, emphasize analyzing data, and using defaults only in the absence of adequate data. This represents a major shift from the former practice of invoking default methodologies or values unless it was judged that there were sufficient data to depart from them. The Guidelines further present a framework for assessing data in order to determine if a mode of action (MOA) can be established, based on a modification of the Bradford-Hill criteria for causality. A similar approach is used by the International Programme on Chemical Safety (IPCS). To illustrate the application of the framework for evaluating animal tumors, three case studies are considered here. In the first example (chloroform carcinogenicity), sufficient data exist to identify the MOA in animals, and the data are used to illustrate the evaluation of the plausibility of the animal MOA in humans, taking into account toxicokinetics and toxicodynamics. In this case, the MOA was judged to be relevant to humans, and was used to determine the approach for the cancer quantitation. In the second example (naphthalene inhalation carcinogenicity), the key question is whether the weight of evidence (WOE) is sufficient to establish the MOA in animals. Atrazine-induced mammary tumors form the final example, illustrating the reasoning used to determine that the tumor MOA in animals was not considered relevant to humans; atrazine is therefore considered not likely to be a human carcinogen.

The United States Environmental Protection Agency (USEPA) has pursued the estimation of risk of adverse health effects from exposure to chemical mixtures since the early 1980s. Methods used to calculate risk estimates of mixtures were often based on single chemical information that required assumptions of dose-addition or response-addition and did not consider possible changes in response due to interaction effects among chemicals. Full factorial designs for laboratory studies can produce interactions information, but these are expensive to perform and may not provide the information needed to evaluate specific environmentally relevant mixtures. In this research, groups of Japanese medaka (Oryzias latipes) embryos were exposed to binary mixtures of benzene and toluene as well as to each of these chemicals alone. Endpoint specific dose-response models were built for the hydrocarbon mixture under an assumption of dose-additivity, using the single chemical dose-response information on benzene and toluene. The endpoints included heart rate, heart rate progression, and lethality. Results included a synergistic response for heart rate at 72 h of development, and either additivity or antagonism for all other endpoints at 96 h of development. This work uses an established statistical method to evaluate the toxicity of an environmentally relevant mixture to ascertain whether interaction effects are occurring, thus providing additional information on toxicity.

The US Environmental Protection Agency (EPA) has developed a framework for human health risk assessment to inform decision making. The National Research Council, in Science and Decisions, recommended that EPA adopt a framework for risk-based decision making, which maximises the utility of risk assessment. The framework considers the NRC's recommendations and builds upon existing agency guidance by emphasising the need to design risk assessments to provide information most applicable to the decision-making process. The framework ties together existing human health guidance, is flexible to accommodate the range of assessments conducted across the agency as well as future advances in risk assessment science, and considers overarching themes including environmental justice and susceptible lifestage risk. The framework integrates the concepts of planning and scoping and problem formulation and provides for incorporation of stakeholder involvement and peer review.

Urinary dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) are among the commonly used biomarkers for inorganic arsenic (iAs) exposure, but may also arise from seafood consumption and organoarsenical pesticide applications. We examined speciated urinary arsenic data from National Health and Nutrition Examination Survey (NHANES) 2009-2010 cycle to assess potential correlations among urinary DMA, MMA, and the organic arsenic species arsenobetaine. Urinary DMA and MMA were positively associated with urinary arsenobetaine, suggesting direct exposure to these species in seafood or metabolism of organic arsenicals to these species, although the biomonitoring data do not directly identify the sources of exposure. The magnitude of association was much larger for DMA than for MMA. The secondary methylation index (SMI, ratio of urinary DMA to MMA) observed in the NHANES program likewise is much higher in persons with detected arsenobetaine than in those without, again suggesting that direct DMA exposure is co-occurring with exposure to arsenobetaine. Urinary MMA was less correlated with organic arsenic exposures than DMA and, therefore, may be a more reliable biomarker for iAs exposure in the general US population. However, given the associations between both MMA and DMA and organic arsenic species in urine, interpretations of the urinary arsenic concentrations observed in the NHANES in the context of potential arsenic exposure should be made cautiously.

The constitutive androstane receptor (CAR) and pregnane X receptor (PXR) are important nuclear receptors involved in the regulation of cellular responses from exposure to many xenobiotics and various physiological processes. Phenobarbital (PB) is a non-genotoxic indirect CAR activator, which induces cytochrome P450 (CYP) and other xenobiotic metabolizing enzymes and is known to produce liver foci/tumors in mice and rats. From literature data, a mode of action (MOA) for PB-induced rodent liver tumor formation was developed. A MOA for PXR activators was not established owing to a lack of suitable data. The key events in the PB-induced liver tumor MOA comprise activation of CAR followed by altered gene expression specific to CAR activation, increased cell proliferation, formation of altered hepatic foci and ultimately the development of liver tumors. Associative events in the MOA include altered epigenetic changes, induction of hepatic CYP2B enzymes, liver hypertrophy and decreased apoptosis; with inhibition of gap junctional intercellular communication being an associative event or modulating factor. The MOA was evaluated using the modified Bradford Hill criteria for causality and other possible MOAs were excluded. While PB produces liver tumors in rodents, important species differences were identified including a lack of cell proliferation in cultured human hepatocytes. The MOA for PB-induced rodent liver tumor formation was considered to be qualitatively not plausible for humans. This conclusion is supported by data from a number of epidemiological studies conducted in human populations chronically exposed to PB in which there is no clear evidence for increased liver tumor risk.

International audience; BACKGROUND: Diverse perspectives have influenced fish consumption choices. OBJECTIVES: We summarized the issue of fish consumption choice from toxicological, nutritional, ecological, and economic points of view; identified areas of overlap and disagreement among these viewpoints; and reviewed effects of previous fish consumption advisories. METHODS: We reviewed published scientific literature, public health guidelines, and advisories related to fish consumption, focusing on advisories targeted at U. S. populations. However, our conclusions apply to groups having similar fish consumption patterns. DISCUSSION: There are many possible combinations of matters related to fish consumption, but few, if any, fish consumption patterns optimize all domains. Fish provides a rich source of protein and other nutrients, but because of contamination by methylmercury and other toxicants, higher fish intake often leads to greater toxicant exposure. Furthermore, stocks of wild fish are not adequate to meet the nutrient demands of the growing world population, and fish consumption choices also have a broad economic impact on the fishing industry. Most guidance does not account for ecological and economic impacts of different fish consumption choices. CONCLUSION: Despite the relative lack of information integrating the health, ecological, and economic impacts of different fish choices, clear and simple guidance is necessary to effect desired changes. Thus, more comprehensive advice can be developed to describe the multiple impacts of fish consumption. In addition, policy and fishery management interventions will be necessary to ensure long-term availability of fish as an important source of human nutrition.

There are often several data sets that may be used in developing a quantitative risk estimate for a carcinogen. These estimates are usually based, however, on the dose-response data for tumor incidences from a single sex/strain/species of animal. When appropriate, the use of more data should result in a higher level of confidence in the risk estimate. The decision to use more than one data set (e.g., representing different animal sexes, strains, species, or tumor sites) can be made following biological and statistical analyses of the compatibility of the these data sets. Biological analysis involves consideration of factors such as the relevance of the animal models, study design and execution, dose selection and route of administration, the mechanism of action of the agent, its pharmacokinetics, any species- and/or sex-specific effects, and tumor site specificity. If the biological analysis does not prohibit combining data sets, statistical compatibility of the data sets is then investigated. A generalized likelihood ratio test is proposed for determining the compatibility of different data sets with respect to a common dose-response model, such as the linearized multistage model. The biological and statistical factors influencing the decision to combine data sets are described, followed by a case study of bromodichloromethane.

People handling anticancer drugs or their wastes may absorb these potent genotoxic agents. The aim of this study was to determine the utility of some general urinary markers among 24 female oncology nurses handling these drugs in comparison with 25 "unexposed" nurses. The markers were the Salmonella typhimurium reverse and forward mutation assays, total thioethers, and D-glucaric acid. The reverse mutation assay was the most specific and sensitive marker for anti-cancer drug exposure. Use of the marker battery was no great advantage as a screening tool relative to use of the reverse mutation assay alone. Better recording of work practices in nurse work logs would have improved interpretation of results.

By all accounts, disinfection of drinking water is one of the major public health triumphs of the 20th century. No human endeavor, however, is without risk; more than 30 years ago it was determined that chlorination of water resulted in formation of disinfection by-products (DBPs). Several of these, such as the trihalomethanes (THMs) and haloacetic acids (HAAs), were subsequently observed to produce cancer in animal models and to have other toxic end points, such as reproductive and developmental effects. Moreover, some of these end points have been associated with consumption of disinfected water in human populations; in particular, an elevated risk for bladder cancer has been observed in published epidemiology studies. Many governments have set limits on the amount of DBPs that may be present in drinking water produced by public systems. The U.S. Environmental Protection Agency (EPA), for example, has regulatory limits of 80 μg total THMs and 60 μg total HAA per liter of water (Richardson et al. 2007). However, regulations must also ensure that efforts to reduce DBPs do not result in water that is impaired due to microbial contamination: This is the microbe–DBP balancing act of minimizing risk while maximizing beneficial effects. In this issue of EHP, a suite of four articles builds upon the hundreds of studies (see Richardson et al. 2007) reported since the first report of the genotoxicity of disinfected water (Loper et al 1978). These articles include a case–control study of gene–environment interaction in bladder cancer and three studies of DBP exposures in swimming pool water and biomarkers of their potential effects among swimmers. In the case–control study, Cantor et al. (2010) estimated associations between bladder cancer and individual DBP exposure estimates based on THM measurements in municipal water sources that were linked to residential history. The authors report that participants who carried a glutathione S-transferase zeta-1 (GSTZ1) rs1046428 polymorphism and were missing one or both copies of GSTT1 appeared to be particularly susceptible to bladder cancer when exposed to relatively high levels of THMs in water [odds ratio = 5.9 (95% confidence interval, 1.8–19.0) for > 49 μg versus ≤ 8 μg THMs/L]. The two susceptibility alleles occurred together in 29% of the Spanish study population (Cantor et al. 2010). Richardson et al. (2010) identified > 100 DBPs in water samples from two indoor pools in Barcelona, Spain (one chlorinated and one brominated). The samples included some nitrogen-containing DBPs that had not been found previously in drinking water, which the authors suggest may have formed due to the presence of nitrogen sources in pool water, such as urine or sweat. Nonetheless, they report that mutagenic potencies of the pool water (based on the Salmonella assay) were similar to that of typical drinking water. Kogevinas et al. (2010) report that bathers in the chlorinated Barcelona pool had an increased frequency of micronuclei in peripheral blood cells (a marker of DNA damage) and evidence of increased systemic exposure to mutagens (based on urinary mutagenicity using the Salmonella assay) after a 40-min swim. Both end points were also associated with the concentrations of brominated THMs—but not chloroform—in the exhaled breath of the swimmers. In addition, Font-Ribera et al. (2010) report that Clara cell secretor protein (CC16), an indicator of increased lung epithelium permeability, was increased after swimming in the same chlorinated pool. As noted by the authors, alterations in Clara cell permeability are thought to play a role in the development of asthma, which has been linked to indoor swimming pool exposure. However, both exercise and DBP exposure could have contributed to the increase in CC16 after swimming. Collectively, these studies provide the clearest evidence to date that disinfected water might be genotoxic and carcinogenic to humans, and that genotype may be a critical factor in susceptibility to bladder cancer in individuals exposed to DBPs. However, these researchers emphasize that their results need to be replicated and note that another case–control bladder cancer study is currently under way by the U.S. National Cancer Institute (National Institutes of Health). How can these data be used by regulators? I suggest again that it is a matter of balance. Swimming is generally considered to be a health-enhancing activity; it can be a good aerobic exercise, contribute to flexibility and muscle strength, and can have positive social aspects. However, after water leaves a public water system and enters a pool, its quality is not regulated at the national level in the United States as it is in some countries, and the Safe Drinking Water Act makes no stipulation that tap water meet any additional requirements for use in pools or spas. Instead, pool water quality is managed at the most local level in the United States, usually by state or local public health departments, and sometimes by pool managers or lifeguards. In the pool balancing act, one must weigh immediate hazards that might result from exposure to microbial pathogens if adequate disinfection levels are not maintained against potential long-term hazards associated with exposure to DBPs. In addition, regulators must also consider the cost of delivering high-quality water to the consumer. One option to decrease the responsibility and expense incurred by public drinking water systems is to improve the quality of source water through pollution prevention and precursor removal. However, a source reduction approach is challenging for swimming pools, because the swimmers themselves are the largest source of nitrogenous substrates and a substantial source of organic matter necessary for DBP formation. What is next for regulatory groups? It may be time to consider the feasibility of a population-based risk assessment for DBPs based on the evolving knowledge of genetic susceptibility to DBP-associated cancer. Any risk management approach for DBPs must be balanced against risk of waterborne disease, without exquisite information on genetic or life-stage susceptibility for these diseases. In addition, increased emphasis on DBPs, or any class of contaminants, will be balanced against the need for research and risk assessment for chemicals not currently addressed by regulations. Tools are available to help in sorting priorities for risk assessment in support of risk management. Also in this issue of EHP, Claxton et al. (2010) review the 40-year history of the Salmonella mutagenicity assay and discuss that history informs the development of 21st century toxicology. The Salmonella mutagenicity assay was used > 30 years ago in the first report of the mutagenic potential of drinking water (Loper et al. 1978), and it continues to be used in hazard identification, as evidenced by the current swimmer studies. In this century, we need to use all of the tools available to us—advanced analytical methods, genomic end points, and engineering approaches—to guarantee the delivery to all of water that is safe for drinking, bathing, and swimming.

The Mouse Lymphoma Expert Workgroup of the International Workshop for Genotoxicity Tests (IWGT) met in Basel, Switzerland in August of 2009. The Workgroup (WG) was tasked with discussing the appropriate top concentration for non-pharmaceuticals that would be required for the conduct of the mouse lymphoma assay (MLA) when sufficient cytotoxicity [to between 10 and 20% relative total growth (RTG)] has not been attained. The WG approached this task by (1) enumerating the various regulatory decisions/use for MLA data, (2) discussing the appropriate assays to which MLA data and assay performance should be compared and (3) discussing all the proposals put forth concerning the top concentration for non-pharmaceuticals. In addition, one of the members presented a summary of a re-evaluation of the National Toxicology Program MLA data using the IWGT harmonized guidance that was underway as a separate (non IWGT) activity, being conducted by two members of the Expert WG. The WG was asked to vote on each of the various proposals for top concentration for when cytotoxicity is not concentration limiting. While there was general agreement that the top concentration for non-pharmaceuticals should be re-evaluated and likely lowered from the current recommended levels, there was no agreement on a specific new recommendation.

There is a need to define exposure-response curves for both Cu excess and deficiency to assist in determining the acceptable range of oral intake. A comprehensive database has been developed where different health outcomes from elevated and deficient Cu intakes were assigned ordinal severity scores to create common measures of response. A generalized linear model for ordinal data was used to estimate the probability of response associated with dose, duration and severity. The model can account for differences in animal species, the exposure medium (drinking water and feed), age, sex, and solubility. Using this model, an optimal intake level of 2.6 mg Cu/d was determined. This value is higher than the current U.S. recommended dietary intake (RDI; 0.9 mg/d) that protects against toxicity from Cu deficiency. It is also lower than the current tolerable upper intake level (UL; 10 mg/d) that protects against toxicity from Cu excess. Compared to traditional risk assessment approaches, categorical regression can provide risk managers with more information, including a range of intake levels associated with different levels of severity and probability of response. To weigh the relative harms of deficiency and excess, it is important that the results be interpreted along with the available information on the nature of the responses that were assigned to each severity score.

The assessment of human cancer risk from chemical exposure requires the integration of diverse types of data. Such data involve effects at the cell and tissue levels. This report focuses on the specific utility of one type of data, namely DNA adducts. Emphasis is placed on the appreciation that such DNA adduct data cannot be used in isolation in the risk assessment process but must be used in an integrated fashion with other information. As emerging technologies provide even more sensitive quantitative measurements of DNA adducts, integration that establishes links between DNA adducts and accepted outcome measures becomes critical for risk assessment. The present report proposes an organizational approach for the assessment of DNA adduct data (e.g., type of adduct, frequency, persistence, type of repair process) in concert with other relevant data, such as dosimetry, toxicity, mutagenicity, genotoxicity, and tumor incidence, to inform characterization of the mode of action. DNA adducts are considered biomarkers of exposure, whereas gene mutations and chromosomal alterations are often biomarkers of early biological effects and also can be bioindicators of the carcinogenic process.

In response to the 2005 revised US Environmental Protection Agency (EPA) Cancer Guidelines, a Risk Assessment Forum's Technical Panel has devised a strategy in which genetic toxicology data combined with other information are assessed to determine whether a carcinogen operates through a mutagenic mode of action (MOA). This information is necessary for EPA to decide whether age-dependent adjustment factors (ADAFs) should be applied to the cancer risk assessment. A decision tree has been developed as a part of this approach and outlines the critical steps for analyzing a compound for carcinogenicity through a mutagenic MOA (e.g., data analysis, determination of mutagenicity in animals and in humans). Agents, showing mutagenicity in animals and humans, proceed through the Agency's framework analysis for MOAs. Cyclophosphamide (CP), an antineoplastic agent, which is carcinogenic in animals and humans and mutagenic in vitro and in vivo, was selected as a case study to illustrate how the framework analysis would be applied to prove that a carcinogen operates through a mutagenic MOA. Consistent positive results have been seen for mutagenic activity in numerous in vitro assays, in animals (mice, rats, and hamsters) and in humans. Accordingly, CP was processed through the framework analysis and key steps leading to tumor formation were identified as follows: metabolism of the parent compound to alkylating metabolites, DNA damage followed by induction of multiple adverse genetic events, cell proliferation, and bladder tumors. Genetic changes in rats (sister chromatid exchanges at 0.62 mg/kg) can commence within 30 min and in cancer patients, chromosome aberrations at 35 mg/kg are seen by 1 hr, well within the timeframe and tumorigenic dose range for early events. Supporting evidence is also found for cell proliferation, indicating that mutagenicity, associated with cytotoxicity, leads to a proliferative response, which occurs early (48 hr) in the process of tumor induction. Overall, the weight of evidence evaluation supports CP acting through a mutagenic MOA. In addition, no data were found that an alternative MOA might be operative. Therefore, the cancer guidelines recommend a linear extrapolation for the risk assessment. Additionally, data exist showing that CP induces mutagenicity in fetal blood and in the peripheral blood of pediatric patients; thus, the ADAFs would be applied.

The XAD-2 resin concentration/elution system for concentration of mutagens contained in urines was optimized for cancer patients who had been administered such antineoplastic agents as adriamycin (ADR; doxorubicin), cyclophosphamide (CP), methotrexate, vincristine, and 5-fluorouracil. In the reverse mutation assay, Salmonella typhimurium strains TA1535 and TA98 differentiated between CP (with S9 fraction) and ADR (without S9), respectively. No dose-response for CP was observed. There was a dose-response to ADR by TM677 in the presence of S9 using a forward mutation assay. However, while the reverse mutation assays successfully detected ADR and CP administration in the presence of each other in terms of urine mutagenicity, the forward mutation assay did not, since unidentified CP metabolites were also detected in the latter. None of these systems detected mutagenic urines from tobacco smokers, although reaction of these urines with beta-glucuronidase allowed this type of source to be detected also.

In 2001, the U.S. Environmental Protection Agency derived a reference dose (RfD) for methylmercury, which is a daily intake that is likely to be without appreciable risk of deleterious effects during a lifetime. This derivation used a series of benchmark dose (BMD) analyses provided by a National Research Council (NRC) panel convened to assess the health effects of methylmercury. Analyses were performed for a number of endpoints from three large longitudinal cohort studies of the neuropsychological consequences of in utero exposure to methylmercury: the Faroe Islands, Seychelles Islands, and New Zealand studies. Adverse effects were identified in the Faroe Islands and New Zealand studies, but not in the Seychelles Islands. The NRC also performed an integrative analysis of all three studies. The EPA applied a total uncertainty factor (UF) of 10 for intrahuman toxicokinetic and toxicodynamic variability and uncertainty. Dose conversion from cord blood mercury concentrations to maternal methylmercury intake was performed using a one-compartment model. Derivation of potential RfDs from a number of endpoints from the Faroe Islands study converged on 0.1 microg/kg/day, as did the integrative analysis of all three studies. EPA identified several areas for which further information or analyses is needed. Perhaps the most immediately relevant is the ratio of cord:maternal blood mercury concentration, as well as the variability around this ratio. EPA assumed in its dose conversion that the ratio was 1.0; however, available data suggest it is perhaps 1.5-2.0. Verification of a deviation from unity presumably would be translated directly into comparable reduction in the RfD. Other areas that EPA identified as significant areas requiring further attention are cardiovascular consequences of methylmercury exposure and delayed neurotoxicity during aging as a result of previous developmental or adult exposure.

Mercury (Hg) cycles in the environment through a series of complex chemical and physical transformations that occur in air, soils, and water bodies. One component of the environmental mercury cycle is the formation of methylmercury (MHg) primarily by aquatic and marine microorganisms and the accumulation of MHg in foodwebs, particularly in piscivorous species. Human consumption of piscivorous fish and other piscivorus animals is the most common pathway of exposure to MHg. For non-carcinogenic toxic endpoints, the U.S. EPA typically develops a Reference Dose (RfD). This is generally interpreted to be a concentration of a chemical which can be consumed on a daily basis over a lifetime without expectation of adverse effect. There is substantial evidence in both animal and humans that MHg is a neurotoxicant in the adult and the child as well as a developmental neurotoxicant for the fetus. Epidemics of MHg poisoning in Japan and Iraq have resulted from high-dose exposures to MHg. In these epidemics adults, children, nursing infants and fetuses were affected by MHg. The epidemics demonstrate that neurotoxicity is the health effect of greatest concern and that effects on the developing human nervous system apparently occur at lower exposures than those affecting the adult nervous system. We describe how the data from the Iraqi MHg epidemic were used to derive the current RfD of 0.1 microgram/Kgbw/day (U.S. EPA, 1995;).

Data from 83 nurses and pharmacists handling antineoplastic drugs and 35 nurse/pharmacist controls who participated in a national study of antineoplastic drug-handling risks were examined to investigate antineoplastic drug exposure. Measures of external exposure included self-completion drug logs and industrial hygiene scans conducted in clinical settings. Internal exposure was measured by urine mutagenicity tests on end-of-week 24-hour urine specimens. To control for potential confounders, the staff was asked to complete food and hobby diaries and to avoid identified mutagenic substances for 1 week before collection of 24-hour urine samples. On the scans of the drug handlers, 13% showed one or more spots of drug contamination on gloved and ungloved hands, gowns, or shoes. Of the 24-hour urine samples, 15% were mutagenic for Salmonella typhimurium: Rates did not differ significantly for drug handlers and controls. Among nurses who both prepared and administered antineoplastics, those with positive mutagenicity tests handled more doses of the drugs, used less skin protection, and had more skin contact with the drugs than those with negative tests. Nurses who only administered the drugs and had positive mutagenicity tests handled fewer doses of drugs than those with negative tests, but they also reported less use of protection and more skin contact. For both groups of nurses, skin contact with antineoplastics was associated with positive mutagenicity test results (p0.01).

(1996). Cancer Risk Assessment: Historical Perspectives, Current Issues, and Future Directions. Drug and Chemical Toxicology: Vol. 19, No. 3, pp. 161-185.

Assessment of human health risks of environmental agents has often been limited to consideration of the potential for the agent to cause cancer or general systemic toxicity after long-term exposure. The U.S. Environmental Protection Agency (U.S. EPA) is increasingly moving toward the development of integrated assessments, which consider all potential health end points including developmental toxicity, neurotoxicity, immunotoxicity, reproductive effects, and germ cell mutagenicity. The U.S. EPA has a responsibility to assess risks to nonhuman species or ecosystems when appropriate data are available. An example of a recent integrated human health and ecological risk assessment can be found in the U.S. EPA Mercury Study Report to Congress. This report covers the following topics in separate volumes: an inventory of anthropogenic mercury emissions in the United States; an exposure assessment using measured and predicted values and including indirect dietary exposure; an evaluation of human health risks; an assessment of ecologic risk wherein water criteria are presented for several wildlife species; an overall integrated characterization of human and nonhuman risk; and a discussion of risk management considerations. In the evaluation of human health risk, genetic toxicology data were considered for three forms of mercury: elemental, inorganic (divalent), and methylmercury. These data were used in judgments of two types of potential health effects (carcinogenicity and germ cell mutagenicity). In assessment of potential carcinogenicity of inorganic and methylmercury, genetic toxicity data were key. Data for clastogenicity in the absence of mutagenicity supported the characterization of inorganic and methylmercury as materials that produce carcinogenic effects only at high, toxic doses. The evidence for clastogenicity, coupled with information on metabolism and distribution, resulted in a judgment of a moderate degree of concern (or weight of evidence) that inorganic mercury can act as a human germ cell mutagen. For methylmercury, the degree of concern for germ cell mutagenicity is high.

4 chlorinated biphenyl and 5 chlorinated dibenzofuran compounds have been evaluated in the reversion assay developed by B.N. Ames using Salmonella typhimurium histidine auxotrophs. All these compounds (2,4,2′,4′-tetrachlorobiphenyl, 3,4,3′,4′-tetrachlorobiphenyl, 4-chlorobiphenyl, 2,4,6,2′,4′,6′-hexachlorobiphenyl, dibenzofuran, 2,9-dichlorodibenzofuran, 3,6-dichlorodibenzofuran, 2,3,7,8-tetrachlorodibenzofuran and octachlorodibenzofuran) were nonmutagenic for strains TA98 and TA100 when tested over a 3-log dose range. They were also not mutagenic whether or not varying concentrations of microsomal extracts (S9) from uninduced rats or from rats induced by several methods were included in the experimental protocol.

The metabolism and growth effects of benzo(a)pyrene (BaP) were studied using a freshwater green alga, Selenastrum capricornutum. Algal cultures were incubated under gold light with BaP added at concentrations of 40, 160, 400, and 1,200 micrograms/liter for the periods of 1-4 days. The metabolites and BaP were identified and quantified from ethyl acetate extracts of both algal cells and incubation medium. The ethyl acetate extracts were evaluated for genotoxicity using a micro-volume Salmonella typhimurium forward mutation assay with resistance to 8-azaguanine for selection. This assay detected the presence of small quantities of BaP and was particularly sensitive to the mutagenicity of BaP diols. Of those extracts prepared from algae and medium from cultures exposed to 400 micrograms BaP/liter (10 micrograms/25 ml culture), only algal cell extracts from one day's growth were mutagenic. In cultures exposed to 1,200 micrograms BaP/liter (30 micrograms/25 ml culture), mutagenic materials were produced or persisted in both algae and media throughout the 4-day incubation. The observed mutagenic response can be attributed in part to the presence of unmetabolized BaP or to BaP diols.

Polycyclic aromatic hydrocarbons (PAH) known to produce carcinogenic and mutagenic effects have been shown to contaminate waters, sediments and soils. While it is accepted that metabolites of these compounds are responsible for most of their biological effects in mammals, their metabolism, and to a large extent their bioactivity, in aquatic plants have not been explored. Cultures of photosynthetic algal species were assayed for their ability to metabolize benzo[a]pyrene (BaP), a carcinogenic PAH under conditions which either permitted (white light) or disallowed (gold light) photooxidation of the compound. Growth of Selenastrum capricornutum, a fresh-water green alga, was completely inhibited when incubated in white light with 160 micrograms BaP/l medium. By contrast concentrations at the upper limit of BaP solubility in aqueous medium had no effect on algal growth when gold light was used. BaP quinones and phenol derivatives were found to inhibit growth of Selenastrum under white light incubation. BaP phototoxicity and metabolism were observed to be species-specific. All 3 tested species of the order Chlorococcales were growth-inhibited by BaP in white light whereas neither the green alga Chlamydomonas reinhardtii nor a blue-green, a yellow-green or an euglenoid alga responded in this fashion. Assays of radiolabeled BaP metabolism in Selenastrum showed that the majority of radioactivity associated with BaP was found in media as opposed to algal cell pellets, that the extent of metabolism was BaP concentration dependent, and that the proportion of various metabolites detected was a function of the light source. After gold light incubation, BaP diols predominated while after white light treatment at equal BaP concentrations, the 3,6-quinone was found in the highest concentration. Extracted material from algal cell pellets and from media was tested for mutagenicity in a forward mutation suspension assay in Salmonella typhimurium using resistance to 8-azaguanine for selection. Direct-acting mutagens were detected in extracted media from incubation of Selenastrum with 400 micrograms BaP/l for 1 day in gold light. Extracts of media from algae incubated in gold light from 1 to 4 days with 1200 micrograms BaP/l were found to have direct-acting mutagens as well as those requiring further metabolism. Media extracts from white light incubations of BaP were mutagenic upon addition of rat liver homogenates. Activity of these materials from white light treatment are largely attributable to unmetabolized BaP.