The evolution of skin notations for occupational risk assessment: a new NIOSH strategy

This article presents an overview of a strategy for assignment of hazard-specific skin notations (SK), developed by the National Institute for Occupational Safety and Health (NIOSH). This health hazard characterization strategy relies on multiple SKs capable of delineating systemic (SYS), direct (DIR), and immune-mediated (SEN) adverse effects caused by dermal exposures to chemicals. One advantage of the NIOSH strategy is the ability to combine SKs when it is determined that a chemical may cause multiple adverse effects following dermal contact (e.g., SK: SYS-DIR-SEN). Assignment of the SKs is based on a weight-of-evidence (WOE) approach, which refers to the critical examination of all available data from diverse lines of evidence and the derivation of a scientific interpretation based on the collective body of data including its relevance, quality, and reported results. Numeric cutoff values, based on indices of toxic potency, serve as guidelines to aid in consistently determining a chemical’s relative toxicity and hazard potential. The NIOSH strategy documents the scientific rationale for determination of the hazard potential of a chemical and the subsequent assignment of SKs. A case study of acrylamide is presented as an application of the NIOSH strategy.     

About hazard and risk assessment: Regulatory approaches in assessing safety in the European Union chemicals legislation

Hazard classification and labelling is the main and basic requirement for all industrial and consumer chemicals in the European Union, if they are not regulated under more specific legislation such as drugs, food ingredients or cosmetics. The first approach in hazard classification is hazard identification describing the hazardous properties of chemicals. Refinements in the classification criteria include the assessment of toxic potency (hazard characterisation) where feasible and the possibility to set higher or lower specific concentration limits for classification. In the past only a minor portion of the classified chemicals underwent a risk assessment including exposure assessment and risk characterisation. Risk assessment will become more frequent with the implementation of REACH. However, as risk assessment is rather labour-intensive even under REACH risk assessment will be performed in a targeted approach for a selected number of chemical substances while hazard classification and labelling will remain the basic approach for all chemicals.     

Binary test battery with KeratinoSens™ and h-CLAT as part of a bottom-up approach for skin sensitization hazard prediction

Skin sensitization is one of the key safety endpoints for chemicals applied directly to the skin. Several integrated testing strategies (ITS) using multiple non-animal test methods have been developed to accurately evaluate the sensitizing potential of chemicals, but there is no regulatory-accepted ITS to classify a chemical as a non-sensitizer. In this study, the predictive performance of a binary test battery with KeratinoSens™ and h-CLAT compared to the local lymph node assay (LLNA) and human data was examined using comprehensive dataset of 203 chemicals. When two negative results indicate a non-sensitizer, the binary test battery provided sensitivity of 93.4% or 94.4% compared with the LLNA or human data. Taking into account the predictive limitations (i.e. high log Kow, pre-/pro-haptens and acyl transfer agents (or amine-reactive)), the binary test battery had extremely high sensitivity comparable to that of the 3 out of 3 ITS where three negative results of the DPRA, KeratinoSens™ and h-CLAT indicate a non-sensitizer. Therefore, the data from KeratinoSens™ or h-CLAT may provide partly redundant information on the molecular initiating event derived from DPRA. Taken together, the binary test battery of KeratinoSens™ and h-CLAT could be used as part of a bottom-up approach for skin sensitization hazard prediction.     

Assessing the safety of cosmetic chemicals: Consideration of a flux decision tree to predict dermally delivered systemic dose for comparison with oral TTC (Threshold of Toxicological Concern)

Threshold of Toxicological Concern (TTC) aids assessment of human health risks from exposure to low levels of chemicals when toxicity data are limited. The objective here was to explore the potential refinement of exposure for applying the oral TTC to chemicals found in cosmetic products, for which there are limited dermal absorption data. A decision tree was constructed to estimate the dermally absorbed amount of chemical, based on typical skin exposure scenarios. Dermal absorption was calculated using an established predictive algorithm to derive the maximum skin flux adjusted to the actual ‘dose’ applied. The predicted systemic availability (assuming no local metabolism), can then be ranked against the oral TTC for the relevant structural class. The predictive approach has been evaluated by deriving the experimental/prediction ratio for systemic availability for 22 cosmetic chemical exposure scenarios. These emphasise that estimation of skin penetration may be challenging for penetration enhancing formulations, short application times with incomplete rinse-off, or significant metabolism. While there were a few exceptions, the experiment-to-prediction ratios mostly fell within a factor of 10 of the ideal value of 1. It can be concluded therefore, that the approach is fit-for-purpose when used as a screening and prioritisation tool.     

Drug excipients,food additives,and cosmetic ingredients probably not carcinogenic to humans reveal a functional specificity for the 2-year rodent bioassay

Regarding carcinogenicity testing, the long-term rodent bioassay (RCB) has been the test required by most regulatory agencies across the world. Nonetheless, due to the lack of knowledge about its specificity, it has been argued that the RCB is unspecific or even invalid. Because of the substantial limitations of epidemiology to identify chemicals probably not carcinogenic to humans (PNCH), it has been very difficult to address the specificity of the RCB. Nevertheless, because mechanistic/pharmacological data are currently recognized as a valid stream of evidence for the identification of chemical hazards, the road is now open to gain insight into the specificity of the RCB. Based on sound mechanistic/pharmacological data that support the classification of chemicals as PNCH, 100 PNCH substances were gathered in this investigation. Contrary to what was previously forecast, in this study, the RCB exhibited a functional specificity that ranged from 83% to 91%, depending on the settings of the testing (2-species vs. rats only, and the nominal maximum tolerated dose). Other contributions of this work were: (a) enabling the comparison, in terms of specificity, between the RCB and the alternative methods that could replace it (eg, Tg.AC mouse, rasH2 mouse); (b) disclosing what the specificity is for alternative methods that were developed using the RCB as the reference standard; and (c) expanding the previous narrow (only seven substances) set of chemicals identified as not likely to be carcinogenic to humans by hazard identification programs.     

Screening of chemicals for human bioaccumulative potential with a physiologically based toxicokinetic model

Human bioaccumulative potential is an important element in the risk assessment of chemicals. Due to the high number of synthetic chemicals, there exists the need to develop prioritisation strategies. The purpose of this study was to develop a predictive tool for human bioaccumulation risk assessment that incorporates not only the chemical properties of the compounds, but also the processes that tend to decrease the concentration of the compound such as metabolisation. We used a generic physiologically based toxicokinetic model that based on in vitro human liver metabolism data, minimal renal excretion and a constant exposure was able to assess the bioaccumulative potential of a chemical. The approach has been analysed using literature data on well-known bioaccumulative compounds and liver metabolism data from the ECVAM database and a subset of the ToxCast phase I chemical library—in total 94 compounds covering pharmaceuticals, plant protection products and industrial chemicals. Our results provide further evidence that partitioning properties do not allow for a reliable screening criteria for human chemical hazard. Our model, based on a 100% intestinal absorption assumption, suggests that metabolic clearance, plasma protein-binding properties and renal excretion are the main factors in determining whether bioaccumulation will occur and its amount. It is essential that in vitro metabolic clearance tests with metabolic competent cell lines as well as plasma protein-binding assays be performed for suspected bioaccumulative compounds.     

Household products: a review

Household products include detergents, cleaners and polishes, bleaches, disinfectants and sterilizers, dust removers, antistatics and deodorizers, office materials, removers, and products for clothing. Many of these contain chemicals that present a risk to those who come into contact with them. This contact may be through inhalation or dermal exposure for human adults, or by ingestion for children. Pets are exposed through ingestion, dermal contact, and inhalation. An emerging class of household products is the fabric refreshers, which may pose a hazard to humans and pets. This review explores the major chemicals expected in typical fabric refreshers, "and their potential hazards to household pets.     

Methods for Assessing Risks of Dermal Exposures in the Workplace

The skin as a route of entry for toxic chemicals has caused increasing concern over the last decade. The assessment of systemic hazards from dermal exposures has evolved over time, often limited by the amount of experimental data available. The result is that there are many methods being used to assess safety of chemicals in the workplace. The process of assessing hazards of skin contact includes estimating the amount of substance that may end up on the skin and estimating the amount that might reach internal organs. Most times, toxicology studies by the dermal route are not available and extrapolations from other exposure routes are necessary. The hazards of particular chemicals can be expressed as “skin notations”, actual exposure levels, or safe exposure times. Characterizing the risk of a specific procedure in the workplace involves determining the ratio of exposure standards to an expected exposure. The purpose of this review is to address each of the steps in the process and describe the assumptions that are part of the process. Methods are compared by describing their strengths and weaknesses. Recommendations for research in this area are also included.     

Methods for assessing risks of dermal exposures in the workplace

The skin as a route of entry for toxic chemicals has caused increasing concern over the last decade. The assessment of systemic hazards from dermal exposures has evolved over time, often limited by the amount of experimental data available. The result is that there are many methods being used to assess safety of chemicals in the workplace. The process of assessing hazards of skin contact includes estimating the amount of substance that may end up on the skin and estimating the amount that might reach internal organs. Most times, toxicology studies by the dermal route are not available and extrapolations from other exposure routes are necessary. The hazards of particular chemicals can be expressed as "skin notations", actual exposure levels, or safe exposure times. Characterizing the risk of a specific procedure in the workplace involves determining the ratio of exposure standards to an expected exposure. The purpose of this review is to address each of the steps in the process and describe the assumptions that are part of the process. Methods are compared by describing their strengths and weaknesses. Recommendations for research in this area are also included.     

Tiered toxicity testing: Evaluation of toxicity-based decision triggers for human health hazard characterization

A set of biologically-based toxicity testing decision triggers was developed and analyzed within a tiered testing and decision-making framework for evaluating potential human health hazards and risks associated with chemical exposures. The proposed three-tiered toxicity testing approach starts from a base set of toxicity studies (acute toxicity, in vitro genetic toxicity, in vitro cytogenetics, repeat dose/subchronic toxicity, developmental toxicity, reproductive toxicity) and then uses the toxicity triggers to identify which specific additional tests are needed to adequately characterize a substance’s hazard potential. The toxicity triggers were initially evaluated using published information for eight chemicals, representing diverse classes. A retrospective validation study was then conducted using seven chemicals which had completed the USEPA’s Voluntary Children’s Chemical Evaluation Program (VCCEP). The toxicity triggers were shown to identify appropriate higher tier tests and to be reasonably predictive of the results expected in higher tiered tests. Employing these toxicity triggers within a tiered testing framework could lead to a reduction in the number of laboratory animals without diminishing the degree of scientific certainty necessary for hazard evaluations. The toxicity triggers appear to be suitable for identifying which specific endpoints and tests warrant further evaluation, and which do not, and for documenting the scientific basis for such decisions.     

A murine model for low molecular weight chemicals: differentiation of respiratory sensitizers (TMA) from contact sensitizers (DNFB)

Exposure to low molecular weight (LMW) chemicals contributes to both dermal and respiratory sensitization and is an important occupational health problem. Our goal was to establish an in vivo murine model for hazard identification of LMW chemicals that have the potential to induce respiratory hypersensitivity (RH). We used a dermal sensitization protocol followed by a respiratory challenge with the evaluation of endpoints typically associated with RH in human disease. Trimellitic anhydride (TMA) was used as a prototype respiratory sensitizer and was compared to the dermal sensitizer; 2,4-dinitrofluorobenzene (DNFB), along with vehicle controls. BALB/c mice were dermally sensitized using two exposure protocols. Mice in both protocols were dermally exposed on experimental days; D-18 and D-17 (abdomen), and D-13 (ear). On D 0 mice received an intratracheal (IT) challenge. The mice in Protocol 2 were abdominally exposed twice with the addition of exposures on D-25 and D-24. Results indicate that mice required the additional dermal sensitization and the IT challenge (Protocol 2) to significantly elevate total IgE in serum and bronchoalveolar lavage fluid (BALF). Additional responses suggestive of RH were seen following Protocol 2, including increases in BALF cell numbers and neutrophils post IT with TMA (but not DNFB). These data suggest that the dermal sensitization and IT challenge followed by evaluation of serum antibodies and lung parameters are a reasonable and logistically feasible approach towards the development of a model for RH responses to LMW chemicals.     

Use of health hazard criteria for estimating the hazard potential of chemicals to water in case of a spill

Accidental spills resulting in severe pollution can occur during transportation or handling of large volumes of chemicals. To address this problem, chemicals are classified according to the level of hazard to man and the environment in order to then define graduated technical standards. Three regulatory examples (enforced or drafted for transport and industrial installations in Europe) covering aspects of limnic as well as sea water are discussed in regard to health aspects of pollution. Whereas for the safety of seagoing tankships an exposure orientated combination of health and environmental aspects is used, for industrial plants in Germany a scoring system based on the European Union's Risk Phrase system is applied. The health-related parameters primarily used for hazard classification are repeated-dose toxicity and acute oral and dermal toxicity. Acute oral toxicity is most widely used because of the ready availability of data. Carcinogenicity is treated as the most important hazard. The report discusses the importance of dermal exposure, aspiration, and endocrine disruption as parameters as well as the importance of health criteria for the protection of aquatic organisms.     

In vitro dermal absorption rate testing of certain chemicals of interest to the Occupational Safety and Health Administration: summary and evaluation of USEPA's mandated testing

In 2004, the United States Environmental Protection Agency (USEPA) published a final test rule in the US Federal Register requiring in vitro dermal penetration rate testing for selected industrial chemicals. The test rule described procedures for determining a permeability coefficient (Kp) and two short-term dermal absorption rates at 10 and 60min using human cadaver skin mounted in an in vitro diffusion cell model. According to the USEPA announcement, the selected chemicals were to be spiked with their radiolabeled form and tested in either water, isopropyl myristate (IPM) or neat depending on their physical character at room temperature, their aqueous solubility, their potential to damage the skin and their ability to achieve the study endpoints as prescribed. Overall, and for the majority of chemicals, the short-term absorption rates were higher at 10min than at 60min and the portion of applied dose remaining in the skin at the end of the exposure period was greater than the portion of dose that had penetrated through the skin and was detected in the receptor solution. In contrast to this, the amount of chemical in the receptor solution at study termination for the Kp (steady-state) experiments was greater than the amount remaining in the skin. For the Kp experiments, which lasted from 2 to 48h, a majority of skins exposed to neat chemical exhibited a reduced barrier function. However, integrity was mostly unaltered for skins from the short-term experiments and Kp experiments using chemicals applied either in water or IPM. Quantitative structure activity relationship (QSAR) model-predicted Kp values were in fair agreement with experimental data for those chemicals that were applied in a water vehicle when the integrity of the skin was not compromised. However, QSAR-derived Kp values were not predictive for those chemicals when applied in IPM vehicle or neat. Absorption predictions, based on the measured Kp and steady-state flux data for chemicals applied in water or neat, respectively, were comparable to measured values at both 10 and 60min. Kp data for chemicals applied in water and the flux values for neat chemicals will be useful for making estimates of skin absorption in occupational settings. Kp measurements for chemicals applied in IPM vehicle are not envisioned to provide useful data for estimating the risk from dermal exposure to chemicals in the workplace. When available, in vitro dermal flux measurements should be combined with toxicity information in order to improve the utility of chemical skin notations.     

Assessing the prediction accuracy of a cure model for censored survival data with long-term survivors: Application to breast cancer data

The Cox proportional hazards cure model is a survival model incorporating a cure rate with the assumption that the population contains both uncured and cured individuals. It contains a logistic regression for the cure rate, and a Cox regression to estimate the hazard for uncured patients. A single predictive model for both the cure and hazard can be developed by using a cure model that simultaneously predicts the cure rate and hazards for uncured patients; however, model selection is a challenge because of the lack of a measure for quantifying the predictive accuracy of a cure model. Recently, we developed an area under the receiver operating characteristic curve (AUC) for determining the cure rate in a cure model (Asano et al., 2014), but the hazards measure for uncured patients was not resolved. In this article, we propose novel C-statistics that are weighted by the patients’ cure status (i.e., cured, uncured, or censored cases) for the cure model. The operating characteristics of the proposed C-statistics and their confidence interval were examined by simulation analyses. We also illustrate methods for predictive model selection and for further interpretation of variables using the proposed AUCs and C-statistics via application to breast cancer data.     

Correlation between chemical suppression of natural killer cell activity in mice and susceptibility to cytomegalovirus: rationale for applying murine cytomegalovirus as a host resistance model and for interpreting immunotoxicity testing in terms of risk of disease.

The purpose of this study was to determine the relationship between chemical suppression of natural killer (NK) cell activity in mice and chemical effects on susceptibility to murine cytomegalovirus (MCMV) infection. The goal was to provide a rational basis for applying MCMV as a host resistance model for immunotoxicity testing and to provide risk assessors some guidance in relating suppression of NK cell activity to enhanced risk of disease. Data from studies with eight chemicals administered in various doses and by various routes were evaluated, and a significant correlation was observed between chemical suppression of virus-augmented NK cell activity and increased mortality due to MCMV infection. In contrast, effects of the same chemical treatments on spontaneous NK cell activity (i.e., basal activity in uninfected mice) did not correlate with effects of these chemicals on mortality due to MCMV. Although chemicals that suppressed spontaneous NK cell activity enhanced infection, the converse was not always true--that is, increased susceptibility to infection and suppression of virus-augmented NK cell activity were observed on three occasions when spontaneous NK cell activity was unaffected. This latter phenomenon plus the fact that for two chemicals spontaneous NK was suppressed at concentrations twofold below that which affected mortality appear to account for the poor statistical correlation. Nevertheless, the data indicate that MCMV is a useful host resistance model to be applied in immunotoxicity testing when suppression of NK cell activity has been demonstrated. However, virus-augmented activity may be a better indicator than spontaneous activity. The data also indicated that suppression of NK cell activity is predictive of increased susceptibility to infection and hence provides qualitative guidance (hazard identification) to risk assessors.     

Relevance of the developmental toxicity of ethanol in the occupational setting: a review

Numerous studies have been conducted investigating the reproductive toxicology of ethanol, the overwhelming majority concerning the adverse effects of consuming alcohol in beverages during pregnancy. Because many of the in vivo studies were designed to model alcoholism, they used comparatively high doses and assessed relatively few endpoints. Outcomes may have been affected by disturbances of metabolism at such high exposures, giving rise to secondary effects on development. The available data on ethanol from "conventional" developmental toxicity study test methods of the type used for regulatory hazard assessment of chemicals are limited. It is in this context, however, i.e. the use of ethanol as an industrial chemical rather than as a component of beverages, that this review is based. Using the usual criteria applied for the purpose of hazard assessment of industrial chemicals, it is concluded that there is no evidence that industrial exposure to ethanol is a developmental toxicity hazard. Developmental toxicity may result from drinking alcoholic beverages, the threshold level for all aspects of which has yet to be de fi ned. This is not, however, considered relevant to the low blood alcohol concentrations resulting from any conceivable inhalation or dermal exposure in the workplace or through the directed use of any consumer product containing ethanol.     

Endocrine effects of chemicals: Aspects of hazard identification and human health risk assessment

Hazard and risk assessment of chemicals with endocrine activity is hotly debated due to claimed non-monotonous dose–response curves in the low-dose region. In hazard identification a clear definition of “endocrine disruptors” (EDs) is required; this should be based on the WHO/IPCS definition of EDs and on adverse effects demonstrated in intact animals or humans. Therefore, endocrine effects are a mode of action potentially resulting in adverse effects; any classification should not be based on a mode of action, but on adverse effects. In addition, when relying on adverse effects, most effects reported in the low-dose region will not qualify for hazard identification since most have little relation to an adverse effect. Non-monotonous dose–response curves that had been postulated from limited, exploratory studies could also not be reproduced in targeted studies with elaborate quality assurance. Therefore, regulatory agencies or advisory bodies continue to apply the safety-factor method or the concept of “margin-of-exposure” based on no observed adverse effect levels (NOAELs) in the risk assessment of chemicals with weak hormonal activity. Consistent with this approach, tolerable levels regarding human exposure have been defined for such chemicals. To conclusively support non-monotonous dose–response curves, targeted experiments with a sufficient number of animals, determination of adverse endpoints, adequate statistics and quality control would be required.