Title:	Quality Assurance of Exposure Models for Environmental Risk Assessment of Substances
Other Titles:	Qualitätssicherung von Expositionsmodellen zur Umweltrisikoabschätzung von Substanzen
Authors:	Schwartz, Stefan
Thesis advisor:	Prof. Dr. rer. nat. Michael Matthies
Thesis referee:	Prof. Dr. rer. nat. Stefan Trapp
Abstract:	Environmental risk assessment of chemical substances in the European Union is based on a harmonised scheme. The required models and parameters are laid down in the Technical Guidance Document (TGD) and are implemented in the EUSES software. An evaluation study of the TGD exposure models was carried out. In particular, the models for estimating chemical intake by humans were investigated. The objective of this study was two-fold: firstly, to develop an evaluation methodology, since no appropriate approach is available in the scientific literature. Secondly, to elaborate applicability and limitations of the models and to provide proposals for their improvement. The principles of model evaluation in terms of quality assurance, model validation and software evaluation were elaborated and a suitable evaluation protocol for chemical risk assessment models was developed. Quality assurance of a model includes internal (e.g. an investigation of the underlying theory) and external (e.g. a comparison of the results with experimental data) validation, and addresses the evaluation of the respective software. It should focus not only on the predictive capability of a model, but also on the strength of the theoretical underpinnings, evidence supporting the model?s conceptualisation, the database and the software. The external validation was performed using a set of reference substances with different physico-chemical properties and use patterns. Additionally, sensitivity and uncertainty analyses were carried out, and alternative models were discussed. Recommendations for improvements and maintenance of the risk assessment methodology were presented. To perform the software evaluation quality criteria for risk assessment software were developed. From a theoretical point of view, it was shown that the models strongly depend on the lipophilicity of the substance, that the underlying assumptions drastically limit the applicability, and that realistic concentrations may seldom be expected. If the models are applied without adjustment, high uncertainties must inevitably be expected. However, many cases were found in which the models deliver highly valuable results. The overall system was classified as a good compromise between complexity and practicability. But several chemicals and classes of chemicals, respectively, with several restrictions were revealed: The investigated models used to assess indirect exposure to humans are in parts currently not applicable for dissociating compounds, very polar compounds, very lipophilic compounds, ions, some surfactants, and compounds in which metabolites provide the problems and mixtures. In a strict sense, the method is only applicable for persistent, non-dissociating chemicals of intermediate lipophilicity. Further limitations may exist. Regarding the software, it was found that EUSES basically fulfils the postulated criteria but is highly complex and non-transparent. To overcome the inadequacies a more modular design is proposed.
URL:	https://osnadocs.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2000090413
Subject Keywords:	Risk assessment; TGD; EUSES; quality assurance; model validation; software evaluation; fate and exposure models; uncertainty analysis; sensitivity analysis; scenario analysis; assumptions; limitations
Issue Date:	4-Sep-2000
Submission date:	4-Sep-2000
Type of publication:	Dissertation oder Habilitation [doctoralThesis]
Appears in Collections:	FB06 - E-Dissertationen

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