Overview and Evaluation of Soil Semi-Field (Higher-Tier) Methods
The use of semi-field (higher-tier) methods aims to implement ecological realism into risk assessment methodologies (for a definition, see Figure 1.1 and Section 4.2). First, Odum (1984) described mesocosms as “bounded systems, partly permeable to their surroundings” and gave therewith the most basic definition of a semi-field approach. He proposed them for use in both ecological and ecotoxicological research. Historically, they are based on approaches developed for ecological questions (e.g., Verhoef 1996; Fraser and Keddy 1997), but as early as the in the mid-1980s a terrestrial model ecosystem was proposed as an ecotoxicological test (Van Voris et al. 1985; Sheppard 1997). These systems can provide improved effect data to evaluate single-species test results and can help to measure ecosystem functions under controlled conditions. They can be used to determine indirect as well as synergistic or compensatory effects of chemicals at ecosystem level and allow for significantly improved assessment of the fate of contaminants in terrestrial ecosystems. Semifield (higher-tier) methods are designed in a way that the advantages of laboratory tests (e.g., standardization, controlled conditions) are combined with the advantages of field studies (natural variability, complex interactions), while at the same time avoiding their disadvantages, like focus on single species or high amount of man power, respectively. In short, while these tests focus on the biological organization level of the population and community, they cover a very wide range of methodological approaches (Figure 4.1).