Emiel Rorije

Evaluation and application of models for the prediction of ready biodegradability in the MITI-I test

Three existing models and one newly developed model for the prediction of ready biodegradability of organic compounds are evaluated by comparing the descriptors they use, and the consistency of the models when applied to the set of High Production Volume Chemicals (HPVC) in the European Union. Linear regression models developed for the OECD showed the best performance in the external validation (84.7% correct), although comparison with the other three models is flawed because of the class specificity of these models. With these models 567 of the 894 compounds could be predicted in the validation. The multivariate statistical model showed the best performance in the external validation (82.7% correct) combined with the broadest applicability of the model. The evaluation of the predictions of the models for the HPVC shows that all models are highly consistent in their prediction of not-ready biodegradability, but much less consistency is seen in the prediction of ready biodegradability. This complies with the observation that all 4 models show better performance in their predictions of not-ready biodegradability.

Combined retrospective analysis of 498 rat multi-generation reproductive toxicity studies: On the impact of parameters related to F1 mating and F2 offspring

The multi-generation reproductive toxicity study (OECD TG 416 and USEPA 870.3800) has been extensively used internationally to assess the adverse effects of substances on reproduction. Recently the necessity of producing a second generation to assess the potential for human health risks has been questioned. The present standardized retrospective analysis of the impact of the second generation on overall study outcome combines earlier analyses and includes 498 rat multi-generation studies representing 438 different tested substances. Detailed assessment of study reports revealed no critical differences in sensitivities between the generations on the basis of a consideration of all endpoints evaluated. This analysis indicates that the second generation mating and offspring will very rarely provide critical information. These findings are consistent with the conclusions of previous retrospective analyses conducted by RIVM, USEPA and PMRA and support adoption of the proposed OECD extended one-generation reproductive toxicity study protocol in regulatory risk assessment testing strategies.

On the Usefulness and Reliability of Existing QSBRs for Risk Assessment and Priority Setting

Abstract The results of a survey of quantitative structure-biodegradability relationships (QSBRs) are presented. The survey was made to evaluate the use of QSBRs for risk assessment and priority setting. It appears that few models can actually be used for legislative purposes. The major reason for this is that many models are either based on biodegradation end-points that are inconvenient for legislative purposes, or are not reproducible, or are based on too few data. It is concluded that single descriptor models cannot accurately predict the biodegradability of a broad range of chemicals. Most of these models therefore apply to narrow subclasses of chemicals only. The development of multiple descriptor models is still rather modest. More generally applicable models are based on molecular fragment contributions to biodegradability. However, for most of these models the chemical domain is uncertain. Despite the fact that none of the models in the survey meet the criteria set for judging a model to be usefu...

On the impact of second generation mating and offspring in multi-generation reproductive toxicity studies on classification and labelling of substances in Europe

The possible impact on classification and labelling decisions of effects observed in second generation parental (P1) and offspring (F2) parameters in multi-generation studies was investigated. This was done for 50 substances classified as reproductive toxicants in Europe, for which a multi-generation study was available. The P1 and F2 effects were compared to parental (P0) and first generation offspring (F1) effects with regard to type of effect as well as incidence, magnitude and severity (IMS), at any dose level. For every study with unique P1/F2 effects, or differences in IMS, the influence of the P1/F2 findings on the classification decision was investigated. Unique P1/F2 generation findings did not play a crucial role in the classification decision of any of the 50 classified substances, except for fenarimol. This substance however provided abundant alerts on the basis of its endocrine activity and developmental neurotoxicity and would therefore also be expected to be identified as a developmental neurotoxicant in an Extended One Generation Reproductive Toxicity Study (EOGRTS). These findings, in addition to the increased number of parameters analysed, increased statistical power and reduced animal use, provide strong further support for replacement of the classical two-generation reproductive toxicity study by the EOGRTS in regulatory reproductive toxicity assessment.

Evaluation of an alternative in vitro test battery for detecting reproductive toxicants in a grouping context.

Previously we showed a battery consisting of CALUX transcriptional activation assays, the ReProGlo assay, and the embryonic stem cell test, and zebrafish embryotoxicity assay as apical tests to correctly predict developmental toxicity for 11 out of 12 compounds, and to explain the one false negative [7]. Here we report on applying this battery within the context of grouping and read across, put forward as a potential tool to fill data gaps and avoid animal testing, to distinguish in vivo non- or weak developmental toxicants from potent developmental toxicants within groups of structural analogs. The battery correctly distinguished 2-methylhexanoic acid, monomethyl phthalate, and monobutyltin trichloride as non- or weak developmental toxicants from structurally related developmental toxicants valproic acid, mono-ethylhexyl phthalate, and tributyltin chloride, respectively, and, therefore, holds promise as a biological verification model in grouping and read across approaches. The relevance of toxicokinetic information is indicated.

Comparison of chemical-induced transcriptional activation of fish and human estrogen receptors: Regulatory implications

Under the current EU chemical regulation REACH (Registration, Evaluation, Authorization and Restriction of Chemicals), revised plant protection products and biocides directives, evaluation of endocrine disrupting properties of chemicals becomes a regulatory need. Transcriptional activation (TA) testing of estrogen receptors (ERs) could be one important first step in the screening and testing of endocrine disrupting chemicals (EDCs) for regulatory purposes. However up to now there is no consensus on which species or subtype of ERs should be used for TA testing. This study collected data from publications on TA testing with fish and human ERs for 90 chemicals, covering strong, moderate, and weak or non-ER binders. Each chemical has been reported at least twice, with differential ER TA values that result from different cellular contexts, from intra-/inter-species and subtypes of ERs and from intra-/inter-laboratory differences. All assays could distinguish the differential transcriptional activity induced by chemicals of strong, moderate, and weak or non-ER binders. It is concluded that transactivation of ERs in one vertebrate species or one subtype of ERs could be extrapolated to other species or subtypes of ERs for the purpose of chemical screening. It is emphasized that results from ER TA assays can only be used in a weight-of-evidence approach for further testing in regulatory programs. These results are of importance for regulatory testing strategies and decision making for EDCs.

The OSIRIS Weight of Evidence approach: ITS for skin sensitisation

Within the EU FP6 project OSIRIS approaches to Integrated Testing Strategies (ITSs) were developed, with the aim to facilitate the use of non-test and non-animal testing information in regulatory risk assessment of chemicals. This paper describes an analytical Weight-of-Evidence (WoE) approach to an ITS for the endpoint of skin sensitisation. It specifically addresses the European chemicals legislation REACH, but the concept is readily applicable to ITS and WoE procedures in other regulatory frameworks, and for other toxicological endpoints. Bayesian statistics are applied to estimate the reliability of a conclusion on the sensitisation potential of a chemical, combining evidence from different information sources such as QSAR model predictions, in vitro and in vivo test results. The methodology allows for adaptation of the weight of individual information sources to account for the different levels of reliability of the individual ITS components. The calculated reliability of the WoE conclusion gives an objective, transparent and reproducible measure to decide if the information requirements for data evaluation are satisfied. Furthermore, in case the WoE is not sufficient, it gives the possibility to evaluate a priori if and how it will be possible to fulfil the information requirements with additional tests and/or model predictions.

COMPUTER-ASSISTED EVALUATION OF ANAEROBIC BIODEGRADATION PRODUCTS

Our objective in this study was to create a computer package which, when challenged by the structure of an organic molecule, will be able to predict the mechanism of its biodegradation in presence of anaerobic bacteria. A series of mechanistic models based on previous studies of the anaerobic biodegradation of organic molecules have been encoded into targetkransform pairs. A total of 384 rules have been coded into a dictionary and made available to our META program. Endowed with this dictionary, the META program accurately predicts the mechanism of anaerobic degradation of molecules. Examples of the results obtained with the program are presented for benzoic acid, and polychlorinated nitrobenzenes. This program complements our previous derivation of equivalent mammal metabolism and aerobic biodegradation simulators.

QSARs for oxidation of phenols in the aqueous environment, suitable for risk assessment

To assess the contribution of oxidation to the overall degradation of compounds in the environment, it would be helpful to have QSAR models which cover a large range of chemicals and/or degradation processes. At present QSAR models for oxidation in the aqueous environment mainly deal with phenols and are restricted to a specific reaction with one oxidant present in the aqueous environment. In this paper we have gathered data on oxidation of phenols with various aqueous phase oxidants to compare the different processes. It is sh own that existing models for oxidation can be extended by using the energy of the highest occupied molecular orbital calculated with semiempirical molecular orbital methods as a descriptor. The results from correlating reaction rate constants with this theoretical descriptor are equal to results using experimentally measured half‐wave potentials. By using PLS analysis on those compounds having multiple response data, a single model comprising all oxidation rate constants with different oxidants is created. This analysis shows that for four out of five oxidants the electronic properties of the compound determine the reaction rate constants. These oxidants are thought to react by the same mechanism, namely outer‐sphere one‐electron oxidation. The fifth oxidant, potassium dichromate, shows a different dependence on the descriptor variables, indicating a different reaction mechanism.

The OSIRIS Weight of Evidence approach: ITS mutagenicity and ITS carcinogenicity

Risk assessment of chemicals usually implies data evaluation of in vivo tests in rodents to conclude on their hazards. The FP7 European project OSIRIS has developed integrated testing strategies (ITS) for relevant toxicological endpoints to avoid unnecessary animal testing and thus to reduce time and costs. This paper describes the implementation of ITS mutagenicity and carcinogenicity in the public OSIRIS webtool. The data requirements of REACH formed the basis for these ITS. The main goal was to implement procedures to reach a conclusion on the adequacy and validity of available data. For the mutagenicity ITS a quantitative Weight of Evidence approach based on Bayesian statistics was developed and implemented. The approach allows an overall quality assessment of all available data for the five types of mutagenicity data requirements: in vitro bacterial mutagenicity, in vitro and in vivo chromosome aberration, in vitro and in vivo mammalian mutagenicity. For the carcinogenicity ITS a tool was developed to evaluate the quality of studies not conforming (entirely) to guidelines. In a tiered approach three quality aspects are assessed: documentation (reliability), study design (adequacy) and scope of examination (validity). The quality assessment is based on expert and data driven quantitative Weight of Evidence.