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The veterinary parasiticide ivermectin was selected as a case study compound within the project ERAPharm (Environmental Risk Assessment of Pharmaceuticals). Based on experimental data generated within ERAPharm and additional literature data, an environmental risk assessment (ERA) was performed mainly according to international and European guidelines. For the environmental compartments surface water, sediment, and dung, a risk was indicated at all levels of the tiered assessment approach. Only for soil was no risk indicated after the lower tier assessment. However, the use of effects data from additional 2-species and multispecies studies resulted in a risk indication for collembolans. Although previously performed ERAs for ivermectin revealed no concern for the aquatic compartment, and transient effects on dung-insect populations were not considered as relevant, the present ERA clearly demonstrates unacceptable risks for all investigated environmental compartments and hence suggests the necessity of reassessing ivermectin-containing products. Based on this case study, several gaps in the existing guidelines for ERA of pharmaceuticals were shown and improvements have been suggested. The action limit at the start of the ERA, for example, is not protective for substances such as ivermectin when used on intensively reared animals. Furthermore, initial predicted environmental concentrations (PECs) of ivermectin in soil were estimated to be lower than refined PECs, indicating that the currently used tiered approach for exposure assessment is not appropriate for substances with potential for accumulation in soil. In addition, guidance is lacking for the assessment of effects at higher tiers of the ERA, e.g., for field studies or a tiered effects assessment in the dung compartment.

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During spring and summer 1999 a ring-test and field-validation study with an open, intact Terrestrial Model Ecosystem (TME) was conducted at four different European sites (Amsterdam, The Netherlands; Bangor, U.K.; Coimbra, Portugal; Flörsheim, Germany). The objective of the study was to establish a standardised method which allows the impact of chemical stressors on terrestrial compartments at ecosystem level to be investigated and possible uses of such data in existing Environmental Risk Assessments (ERAs) for chemicals to be evaluated. This issue of Ecotoxicology presents in a series of papers the results of the TME ring-test and field-validation study. Additionally, results derived from an open-homogeneous terrestrial microcosm (Integrated Soil Microcosm, ISM) are included in this series as a separate paper. In this first paper of the series background information on the planning and organisation of the study are given. The conceptual approach and the design of the study with TMEs are briefly outlined, based on the scientific discussion on the use of terrestrial microcosms in ecology and applied environmental sciences during the last 25 years. Further, some suggestions are presented on the selection of measurement endpoints to quantify structural and functional aspects of terrestrial ecosystems. Finally, the main results of the TME-study are summarised and conclusions are drawn on the technical feasibility of TMEs, their comparability with field studies and the potential use of TMEs in ERA.