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Abstract: In an age when vector-borne diseases are emerging worldwide, personal protective measures are essential for shielding soldiers and other exposed persons from arthropod attack. The development of permethrin-impregnated clothing has been one recent advance in protecting persons at-risk. However, to date risk assessment has not been performed related to wearing permethrin-impregnated clothing over longer time periods. Therefore, this paper describes relevant toxicological aspects of permethrin and estimates the extent of dermal permethrin uptake by soldiers wearing impregnated uniforms by determining urine metabolites of permethrin. The exposure monitoring conducted in wearers of untreated uniforms did not show any signs of increased permethrin uptake and was similar to that of the general population in Germany. By contrast, studies involving the soldiers wearing permethrin-impregnated uniforms identified far higher internal exposure, the amounts of urine metabolites clearly above the reference value for the background exposure of the German population at large. Comparing the median excretion values, an approximately 200 times higher exposure can be assumed. The excretion levels of the subject with the maximum amount of metabolites correspond to an internal exposure of around 5–6μg/kg body weight and day thereby considering that biomonitoring could not take all urine metabolites and other elimination routes into account. Based on an oral absorption rate of 50%, the internal dose of 5–6μg/kg body weight and day would correspond to an oral uptake of permethrin which is around 20% of the ADI value of 50μg/kg body weight and day. In addition, based on these data and using a dermal absorption rate of 2% the permethrin dose reaching the skin was estimated to be 250μg/kg body weight and day. Considering a standard body weight and the area covered by the uniform, an exposure level of about 1.25μgpermethrin/cm2 skin and day can be calculated. Clinical subjective symptoms were recorded by means of a self-reporting questionnaire which has been developed and used for this specific purpose in environmental outpatient departments in both groups (wearers of impregnated versus non-impregnated uniforms). Only minor sensory impairments were identified in one of the studies (Kabul/Afghanistan) which may represent skin paraesthesiae. Based on these results, it can be assumed that the normal use of permethrin-treated uniforms does not affect human health to a clinical relevant extent. We recommend that the release rate of permethrin from the textile material should be strictly monitored by means of a quality assurance method. It should comply with standards to which the results of this study may contribute. [Copyright &y& Elsevier]

Provides an international perspective on the use of toxicokinetic and toxicodynamic data in risk assessment of chemicals. Guidance for the use of data in development of chemical-specific adjustment factors; Kinetics of a chemical encompassing absorption, distribution, metabolism and excretion on animal and human testing; Identification of the active chemical moiety.

In the absence of toxicological data, as it is the case for, e.g. naturally occurring substances and chemicals underlying the new European chemicals legislation, distinct tools to derive quantitative toxicological data are of particular interest with regard to risk assessment of substances humans are repeatedly exposed. The software package TOPKAT 6.2 version 3.1 (Accelrys Inc., San Diego, USA) is a commercially available tool containing a (sub)chronic oral low observed adverse level (LOAEL) prediction model constructed by using structures and LOAELs of 393 chemicals contained in publicly accessible data banks. Applying this tool, we tested the prediction of (sub)chronic LOAELS for 807 industrial chemicals (purity ≥ 95%) by comparing the predicted values with their experimental LOAELs derived from repeated dose animal experiments performed according to standard guidelines. For 460 chemicals, a prediction could not be performed because of exclusion criteria defined in the system. They had either a lower LD50 as the predicted LOAEL ( n = 214) were outside the optimum prediction space which defines the domain of applicability ( n = 175), were used in the training data set ( n = 155), were not known to the system ( n = 50) or fulfilled other criteria for data exclusion ( n = 21). Of the remaining 347 substances, 34 to 62% LOAELs were predicted within a range of 1/5 and fivefold of the experimental LOAEL (factor 5), whereas 84 and 99% of the predicted LOAELs were within a range of 1/100 and 100-fold indicating high uncertainty of the prediction. Hence, a refined prediction tool is highly warranted. However, the uncertainty of the prediction could be accounted for if an additional factor of 100 is applied in addition to standard default adjustment factor of 100 which would result in an adjustment factor of 10,000 to be able to use a predicted NOAEL for risk assessment.. [ABSTRACT FROM AUTHOR]

Clearly, given values for renal plasma clearance (CLren) and unbound fraction (Fr), deductions from CLren = Fr × GFR + CLsec - CLre with respect to tubular secretion (CLsec) and reabsorption (CLre) critically depend on the GFR. As long as secretion, in particular secretion with the involvement of OAT2 and OAT3 cannot be ruled out, sex differences in rats have to be interpreted with highest caution with respect to extrapolating the results to humans. 7 Kim S-J, Choi E-J, Choi G-W, Lee Y-B, Cho H-Y. Exploring sex differences in human health risk assessment for PFNA and PFDA using a PBPK model. [Extracted from the article]

The present scientific opinion deals with the evaluation of the safety of nisin (E 234) in the light of new toxicological data and with the proposed extension of use in unripened cheese and heat-treated meat products. Nisin (E 234) is currently an authorised food additive in the EU under Annex II of Regulation (EC) 1333/2008 for use in several food categories. The safety of nisin (E 234) as a food additive has been evaluated in 2006 by the EFSA Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food, where an acceptable daily intake (ADI) of 0.13 mg/kg body weight (bw) was confirmed as previously established by Scientific Committee on Food (SCF). In addition to the studies previously evaluated by EFSA in 2006, the Panel considered in the present opinion, data from a new subchronic toxicity study. No adverse effects were observed in a repeated dose oral toxicity study in which rats were administered nisin A for 90 days. A no observed adverse effect level (NOAEL) of 225 mg nisin A/kg bw per day, the highest dose tested, was identified for this study. Using this NOAEL, an ADI of 1 mg nisin A/kg bw per day for nisin (E 234) was calculated applying a default uncertainty factor of 200 for extrapolation of subchronic to chronic exposure and inter- and intraspecies variability. The Panel calculated exposure estimates for both the current and the proposed uses based on the data available in the EFSA Comprehensive Database. The Panel considered that the overall exposure estimate was below the new ADI for nisin A for all population groups. The Panel concluded that the proposed extension of use of nisin (E 234) as a food additive in unripened cheese (at maximum level of 12 mg/kg) and in heat-treated meat products (at maximum level of 25 mg/kg) would not be of safety concern. [ABSTRACT FROM AUTHOR]

The TTC concept uses toxicological data from animal testing to derive generic human exposure threshold values (TTC values), below which the risk of adverse effects on human health is considered to be low. It uses distributions of no-observed-adverse-effect levels (NOAELs) for substances. The 5th percentile value is divided by an uncertainty factor (100) to give a TTC value. As the toxicological data underpinning the TTC concept are from tests with oral exposure, the exposure is to be understood as an external oral exposure. For risk assessment of substances with a low absorption (by the oral route, or through skin), the internal exposure is more relevant than the external exposure. European legislation allows that tests might not be necessary for substances with negligible absorption with low internal exposure. The aim of this work is to derive internal TTC values to allow the TTC concept to be applied to situations of low internal exposure. The external NOAEL of each chemical of three databases (Munro, ELINCS, Food Contact Materials) was multiplied by the bioavailability of the individual chemical. Oral bioavailability was predicted using an in silico prediction tool (ACD Percepta). After applying a reduced uncertainty factor of 25, we derived internal TTC values. For Cramer class I, the internal TTC values are 6.9 μg/kg bw/d (90 % confidence interval: 3.8-11.5 mg/kg bw/d); for Cramer class II/III 0.1 μg/kg bw/d (90 % confidence interval: 0.08-0.14 μg/kg bw/d). [ABSTRACT FROM AUTHOR]

There is a need of guidance on how local irritancy data should be incorporated into risk assessment procedures, particularly with respect to the derivation of occupational exposure limits (OELs). Therefore, a board of experts from German committees in charge of the derivation of OELs discussed the major challenges of this particular end point for regulatory toxicology. As a result, this overview deals with the question of integrating results of local toxicity at the eyes and the upper respiratory tract (URT). Part 1 describes the morphology and physiology of the relevant target sites, i.e., the outer eye, nasal cavity, and larynx/pharynx in humans. Special emphasis is placed on sensory innervation, species differences between humans and rodents, and possible effects of obnoxious odor in humans. Based on this physiological basis, Part 2 describes a conceptual model for the causation of adverse health effects at these targets that is composed of two pathways. The first, 'sensory irritation' pathway is initiated by the interaction of local irritants with receptors of the nervous system (e.g., trigeminal nerve endings) and a downstream cascade of reflexes and defense mechanisms (e.g., eyeblinks, coughing). While the first stages of this pathway are thought to be completely reversible, high or prolonged exposure can lead to neurogenic inflammation and subsequently tissue damage. The second, 'tissue irritation' pathway starts with the interaction of the local irritant with the epithelial cell layers of the eyes and the URT. Adaptive changes are the first response on that pathway followed by inflammation and irreversible damages. Regardless of these initial steps, at high concentrations and prolonged exposures, the two pathways converge to the adverse effect of morphologically and biochemically ascertainable changes. Experimental exposure studies with human volunteers provide the empirical basis for effects along the sensory irritation pathway and thus, 'sensory NOAEC' can be derived. In contrast, inhalation studies with rodents investigate the second pathway that yields an 'irritative NOAEC.' Usually the data for both pathways is not available and extrapolation across species is necessary. Part 3 comprises an empirical approach for the derivation of a default factor for interspecies differences. Therefore, from those substances under discussion in German scientific and regulatory bodies, 19 substances were identified known to be human irritants with available human and animal data. The evaluation started with three substances: ethyl acrylate, formaldehyde, and methyl methacrylate. For these substances, appropriate chronic animal and a controlled human exposure studies were available. The comparison of the sensory NOAEC with the irritative NOAEC (chronic) resulted in an interspecies extrapolation factor (iEF) of 3 for extrapolating animal data concerning local sensory irritating effects. The adequacy of this iEF was confirmed by its application to additional substances with lower data density (acetaldehyde, ammonia, n-butyl acetate, hydrogen sulfide, and 2-ethylhexanol). Thus, extrapolating from animal studies, an iEF of 3 should be applied for local sensory irritants without reliable human data, unless individual data argue for a substance-specific approach. [ABSTRACT FROM AUTHOR]

Highlights: [•] Animal-free risk assessment must increasingly use human toxicokinetics predictions. [•] Only human physiologically-based toxicokinetic (PBTK) modelling can serve this need. [•] Freely-available open source PBTK modelling platforms are lacking largely. [•] In vitro and in silico (QSAR) tools to meaure and predict needed parameters are rather scarce. [•] Presented are a state of the art overview and five high priority recommendations. [Copyright &y& Elsevier]

Abstract: Toxicokinetics (TK) is the endpoint that informs about the penetration into and fate within the body of a toxic substance, including the possible emergence of metabolites. Traditionally, the data needed to understand those phenomena have been obtained in vivo. Currently, with a drive towards non-animal testing approaches, TK has been identified as a key element to integrate the results from in silico, in vitro and already available in vivo studies. TK is needed to estimate the range of target organ doses that can be expected from realistic human external exposure scenarios. This information is crucial for determining the dose/concentration range that should be used for in vitro testing. Vice versa, TK is necessary to convert the in vitro results, generated at tissue/cell or sub-cellular level, into dose response or potency information relating to the entire target organism, i.e. the human body (in vitro–in vivo extrapolation, IVIVE). Physiologically based toxicokinetic modelling (PBTK) is currently regarded as the most adequate approach to simulate human TK and extrapolate between in vitro and in vivo contexts. The fact that PBTK models are mechanism-based which allows them to be ‘generic’ to a certain extent (various extrapolations possible) has been critical for their success so far. The need for high-quality in vitro and in silico data on absorption, distribution, metabolism as well as excretion (ADME) as input for PBTK models to predict human dose–response curves is currently a bottleneck for integrative risk assessment. [Copyright &y& Elsevier]

Abstract: Risk assessment for acute airborne exposure to volatile organic compounds (VOCs), including exposure to chemical warfare agents, requires consideration of local and systemic effects at high concentrations. The operating procedure developed by the US Acute Exposure Guideline Level (AEGL) committee has gained special attention, in part because of the international collaboration in the project. The procedure defines three levels (AEGL-1: discomfort; AEGL-2: irreversible or other serious, long-lasting adverse effects; AEGL-3: life-threatening effects or death) for different exposure times (10 and 30min, and 1, 4 and 8h). In this article, the methodology for deriving AEGL values is reported. Extending the areas covered by the existing AEGL methodology, sensitive subpopulations are dealt with in more detail. Sensitive persons are expected to suffer from stronger effects when exposed to a given external concentration. Using a kinetic model with the sample substance dichloromethane (DCM), the higher internal exposure of children is quantified and compared to a healthy, young adult. The difference is shown to depend on age, on dose, and on duration of exposure. Furthermore, several ways are presented to derive AEGL values for exposure times which differ from the exposure duration in animal studies (‘time scaling’). In comparison to the conventional procedure, the alternative approaches are based on mechanistic models of the toxicodynamic effect. Use of these models results in AEGL values which are biologically justified. [Copyright &y& Elsevier]

Describing the toxicological profile of a substance is the first step required for risk assessment. Although a wide range ofin vitromethods are widely used to characterise toxicological properties including toxicokinetics, regulatory acceptance is mainly confined toin vitrotests which investigate genotoxic end-points.In vitrotests have been proposed for the endpoints acute toxicity, repeated dose toxicity and toxicity to reproduction which encompass the minimum requirements in the OECD SIDS programme. However, until now, limitations of the proposed tests preclude their application in a regulatory framework. Presently,in vitrotests play a major role in obtaining information on mechanism of toxicity with the perspective to be able to identify pathways of toxic responses by applying toxicogenomics techniques. Physiologically based toxicokinetic modelling is using data fromin vitrostudies to build up the model for a specific compound. Information from both areas is incorporated into the risk assessment to derive compound-specific safety factors, which account for species differences and for the variability among the human population, including possible sensitive subpopulations. Future developments to further enhance the use ofin vitromethods in regulatory toxicology include the development of (Q)SAR approaches supplemented by mechanisms of toxicity, which can be addressed by developing methods of molecular toxicology. [ABSTRACT FROM AUTHOR]

Discusses the risk of children exposed to volatile organic compounds. Quantification of the age-dependent differences in the internal exposure children during acute inhalation of volatile organic compounds; Influence of the chemical's properties on the calculated ratios of the arterial concentrations; Factors contributing to the increase of arterial concentrations.