New aspects in deriving health-based guidance values for bromate in swimming pool water.

Bromate, classified as a EU CLP 1B carcinogen, is a typical by-product of the disinfection of drinking and swimming pool water. The aim of this study was (a) to provide data on the occurrence of bromate in pool water, (b) to re-evaluate the carcinogenic MOA of bromate in the light of existing data, (c) to assess the possible exposure to bromate via swimming pool water and (d) to inform the derivation of cancer risk-related bromate concentrations in swimming pool water. Measurements from monitoring analysis of 229 samples showed bromate concentrations in seawater pools up to 34 mg/L. A comprehensive non-systematic literature search was done and the quality of the studies on genotoxicity and carcinogenicity was assessed by Klimisch criteria (Klimisch et al., Regul Toxicol Pharmacol 25:1-5, 1997) and SciRAP tool (Beronius et al., J Appl Toxicol, 38:1460-1470, 2018) respectively. Benchmark dose (BMD) modeling was performed using the modeling average mode in BMDS 3.1 and PROAST 66.40, 67 and 69 (human cancer BMDL10; EFSA 2017). For exposure assessment, data from a wide range of sources were evaluated for their reliability. Different target groups (infants/toddlers, children and adults) and exposure scenarios (recreational, sport-active swimmers, top athletes) were considered for oral, inhalation and dermal exposure. Exposure was calculated according to the frequency of swimming events and duration in water. For illustration, cancer risk-related bromate concentrations in pool water were calculated for different target groups, taking into account their exposure using the hBMDL10 and a cancer risk of 1 in 100,000. Convincing evidence was obtained from a multitude of studies that bromate induces oxidative DNA damage and acts as a clastogen in vitro and in vivo. Since statistical modeling of the available genotoxicity data is compatible with both linear as well as non-linear dose-response relationships, bromate should be conservatively considered to be a non-threshold carcinogen. BMD modeling with model averaging for renal cancer studies (Kurokawa et al., J Natl. Cancer Inst, 1983 and 1986a; DeAngelo et al., Toxicol Pathol 26:587-594, 1998) resulted in a median hBMDL10 of 0.65 mg bromate/kg body weight (bw) per day. Evaluation of different age and activity groups revealed that top athletes had the highest exposure, followed by sport-active children, sport-active adults, infants and toddlers, children and adults. The predominant route of exposure was oral (73-98%) by swallowing water, followed by the dermal route (2-27%), while the inhalation route was insignificant (< 0.5%). Accepting the same risk level for all population groups resulted in different guidance values due to the large variation in exposure. For example, for an additional risk of 1 in 100,000, the bromate concentrations would range between 0.011 for top athletes, 0.015 for sport-active children and 2.1 mg/L for adults. In conclusion, the present study shows that health risks due to bromate exposure by swimming pool water cannot be excluded and that large differences in risk exist depending on the individual swimming habits and water concentrations.

Time extrapolation in regulatory risk assessment: The impact of study differences on the extrapolation factors.

In human risk assessment, time extrapolation factors (EFs) account for differences in exposure duration of experimental studies. We calculated EFs based on N(L)OEL (no (lowest) observed effect level) ratios, dividing shorter-term by longer-term values. The 'oral' datasets comprised 302 EFs (subacute-subchronic) and 1059 EFs (subchronic-chronic). The 'inhalation' datasets contained 67 EFs (subacute-subchronic) and 226 EFs (subchronic-chronic). The experimental EF distribution oral:subchronic-chronic showed that study parameters like deviation in dose selection and spacing influence mainly the data variance. Exclusion of these influences led to a dataset representing more realistically the difference of N(L)OELs with prolonged treatment. This dataset showed a GM of 1.5, indicating that the impact of a longer treatment period on the study N(L)OEL is on average not high. A factor of 1.5 seemed to be also sufficiently conservative for subacute-subchronic and subchronic-chronic extrapolation (inhalation or oral exposure). EFs for groups of similar compounds did not differ, but for compounds with low and high NOEL values. Relatively toxic compounds (GM 1) might thus not require time extrapolation. Within and between chemical variance was analysed in the dataset oral:subchronic-chronic (GSD 4.8). The variance between chemicals should be considered within extrapolation by selecting an appropriate percentile for which a chemical variance factor is suggested. In risk assessment, often a combination of EFs is required. Our analysis indicates that such a combination will result in an accumulation of non-toxicological variance and therefore unrealistically high EFs. Further evaluations are needed to identify appropriate chemical variance factors for these situations.

Inhalation TTC values: A new integrative grouping approach considering structural, toxicological and mechanistic features.

The present publication describes an integrative grouping concept to derive threshold values for inhalation exposure. The classification scheme starts with differences in toxicological potency and develops criteria to group compounds into two potency classes, namely toxic (T-group) or low toxic (L-group). The TTC concept for inhalation exposure is based on the TTC RepDose data set, consisting of 296 organic compounds with 608 repeated-dose inhalation studies. Initially, 21 structural features (SFs) were identified as being characteristic for compounds of either high or low NOEC values (Schüürmann et al., 2016). In subsequent analyses these SF groups were further refined by taking into account structural homogeneity, type of toxicological effect observed, differences in absorption, metabolism and mechanism of action (MoA), to better define their structural and toxicological boundaries. Differentiation of a local or systemic mode of action did not improve the classification scheme. Finally, 28 groups were discriminated: 19 T-groups and 9 L-groups. Clearly distinct thresholds were derived for the T- and L-toxicity groups, being 2 × 10(-5) ppm (2 µg/person/day) and 0.05 ppm (4260 µg/person/day), respectively. The derived thresholds and the classification are compared to the initial mainly structure driven grouping (Schüürmann et al., 2016) and to the Cramer classification.

Incorporating potency into EU classification for carcinogenicity and reproductive toxicity.

Although risk assessment, assessing the potential harm of each particular exposure of a substance, is desirable, it is not feasible in many situations. Risk assessment uses a process of hazard identification, hazard characterisation, and exposure assessment as its components. In the absence of risk assessment, the purpose of classification is to give broad guidance (through the label) on the suitability of a chemical in a range of use situations. Hazard classification in the EU is a process involving identification of the hazards of a substance, followed by comparison of those hazards (including degree of hazard) with defined criteria. Classification should therefore give guidance on degree of hazard as well as hazard identification. Potency is the most important indicator of degree of hazard and should therefore be included in classification. This is done for acute lethality and general toxicity by classifying on dose required to cause the effect. The classification in the EU for carcinogenicity and reproductive toxicity does not discriminate across the wide range of potencies seen (6 orders of magnitude) for carcinogenicity and for developmental toxicity and fertility. Therefore potency should be included in the classification process. The methodology in the EU guidelines for classification for deriving specific concentration limits is a rigorous process for assigning substances which cause tumours or developmental toxicity and infertility in experimental animals to high, medium or low degree of hazard categories by incorporating potency. Methods are suggested on how the degree of hazard so derived could be used in the EU classification process to improve hazard communication and in downstream risk management.

Sensitivity of different generations and developmental stages in studies on reproductive toxicity.

Numerous studies on reproductive toxicity are expected to be necessary under the EU program on Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH). Therefore, it is important to analyse existing testing strategies including also the recently implemented extended one-generation reproduction toxicity study (EOGRTS, OECD guideline 443). For this purpose the responsiveness of the different generations and developmental stages in studies on reproductive toxicity is analysed and critical targets of reproductive toxicity are identified by using the Fraunhofer FeDTex database. The F1 generation is identified as most responsive generation in more than 50% of one-generation and multi-generation reproduction studies. Within the F1 generation the adult stage is mostly affected compared to the prenatal or postnatal stage. The target analysis in F1 has revealed alterations in body weight as highly sensitive for all developmental stages. Other important targets are the liver, kidney, testes, prostate, sperm parameters as well as developmental landmarks. The findings in the F2 generation have shown a higher responsiveness than F1 only in 3% of the studies. Although in 29 studies new effects are observed in F2 offspring compared to F1 irrespective of dose levels, overall no severe new effects have emerged that would change classification and labelling and justify an F1 mating. The presented data support the importance of F1 for risk assessment and demonstrate that the study design of the EOGRTS is a suitable alternative to two-generation studies. However, compared to a conventional one-generation study the EOGRTS may identify additional effects but will change risk assessment with respect to NOELs only in rare cases.

Relevance of non-guideline studies for risk assessment: the coverage model based on most frequent targets in repeated dose toxicity studies.

A common challenge for human risk assessment is the quality of the available animal studies. Non-guideline studies are often limited for different aspects of study design and documentation. Within this publication the relevance of a limited scope of examination is discussed. Preliminary analyses of the RepDose database have shown that liver, body weight, kidney and clinical symptoms are frequently affected in oral repeated dose toxicity in rats and mice (Bitsch et al., 2006), while many other targets are seldom affected. As most of these targets are investigated frequently also in non-guideline studies, it is likely that they provide a reliable NOEL, although the full spectrum of endpoints has not been covered. Based on RepDose data we investigate the relevance of individual targets for determining the LOEL and the consequences for risk assessment. The resulting coverage model for subchronic oral rat studies includes up to six targets and an additional assessment factor for LOEL extrapolation. It can be applied to assess the reliability of non-guideline studies with respect to the scope of examination. Furthermore the application of the coverage model to other databases will increase and/or specify the chemical domain and reveal respective targets as well as effects.

Evaluation of time extrapolation factors based on the database RepDose.

In chemical risk assessment for many substances only short-term animal studies are available for the evaluation of long-term human exposure. Therefore usually extrapolation factors (EF) are used to extrapolate NOAELs from existing short-term studies to NOAELs for long term exposure. In this report time EFs are derived, based on NOEL/C or LOEL/C ratios (short term N(L)OEL/long term N(L)OEL) from the large datasets of the database RepDose (www.fraunhofer-repdose.de) on repeated dose toxicity for oral or inhalation administration. Within a tiered approach several sources of variability, e.g. use of LOEL/C ratios or differences in dose spacing were analyzed and if needed subsequently excluded. The reduction of data variability resulted in "final" EFs datasets, which are as far as possible based on compound-specific, time-dependent differences in toxicity. For distribution functions of oral repeated dose toxicity studies characterised by GM, GSD and 90th percentiles the following data are obtained: subacute-to-subchronic - GM 1.3, GSD 2.4, 90th 4.0, subacute-to-chronic - GM 3.4, GSD 3.7, 90th 18.2, and subchronic-to-chronic - GM 1.4, GSD 2.1, 90th 3.6. The number of data for inhalation exposure is limited, but with regard to systemic toxicity the derived EFs confirm the respective oral EFs.

Evaluation of inhalation TTC values with the database RepDose.

The thresholds of toxicological concern (TTCs) define limit values for substances of unknown toxicity below which dietary intake is considered to be of no concern to human health. The TTC concept has already been used for risk assessment of e.g. food contaminants or flavoring substances and is in discussion to be applied to other classes of compounds such as cosmetic ingredients, household products, non-relevant metabolites in drinking water, and impurities in pharmaceuticals. The present publication aimed to evaluate whether the current TTC concept can also be applied to define limit values for inhalation exposure, using a data set of 203 industrial chemicals from the database RepDose. It has been shown, that the NOEC values in classes 1, 2, and 3 are distributed over six orders of magnitude resulting in a considerable overlap between the distribution curves for the three classes. Inhalation thresholds for Cramer classes 1 (compounds likely to be of low-toxicity), 2 (compounds likely to be of moderate toxicity), and 3 (compounds suspect for high toxicity) were analyzed close to the approach described by Munro for oral TTCs. The 5th percentiles NOEC of Cramer classes 1-3 result in thresholds of 1.5×10(-3) ppm for Cramer class 1 and 2.2×10(-5) ppm for Cramer class 3. A threshold could not be derived for class 2 because of the small number of compounds available. If calculated as body doses, the inhalation thresholds for classes 1 and 3 (71 and 4 µg/person/d, respectively) are considerably lower than the oral thresholds derived by Munro (1800 and 90 µg/person/d). It has been shown that one reason for this difference is the high sensitivity of the respiratory tract to local effects. In a next step, the values obtained were further refined. If organophosphates or compounds with structural alerts for genotoxicity are excluded, the TTC in Cramer class 1 increases, whereas the TTC in Cramer class 3 remains the same. Based on these analyses two inhalation TTCs for non-genotoxic compounds are proposed: 3.6×10(-3) ppm (180 µg/person/d) for Cramer class 1 and 2.4×10(-5)ppm (4 µg/person/d) for Cramer class 3.

Case of fulminant leptospirosis in a renal transplant patient.

We present a case of fulminant leptospirosis that was acquired in the suburban area by a 48-year-old male renal transplant recipient. He developed acute renal and hepatic failure with profound jaundice. Spirochetes were identified on liver biopsy. Weil's disease was suspected, and the diagnosis was further supported by a positive serum Leptospira interrogans icterohaemorrhagiae antibody titer. Unfortunately, he suffered from recurrent lower gastrointestinal bleeding, had a prolonged hospital course, and eventually succumbed to overwhelming sepsis. This case is the third report to our knowledge of leptospirosis in a renal transplant recipient in the English literature.