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Establishing Causal Relationships between Environmental Stressors and Biological Effects in Field Studies

This series of papers is largely derived from presentations at two sessions of the annual Society of Environmental Toxicology and Chemistry (SETAC) meetings in 2000 and 2001 related to establishing causality between stressors and biological effects. These sessions addressed a wide range of studies focused on the difficult problem of demonstrating causal relationships between environmental stressors and effects on biological components of natural ecosystems. The sessions were designed along the lines of increasing biological complexity, and the papers in this series are basically presented in this same order of increasing complexity. The series begins with a review of the processes that have been used to establish causality, including a discussion of various approaches that have been used to attempt to establish causal relationships in field studies including the weight-of-evidence approach. At the end of the first paper, seven standard weightof-evidence criteria are provided which each subsequent author has used to present their argument for causality in a variety of case history studies. Eight case study papers are presented in series including biomolecular and biochemical alterations, impairments in organ structure and function, effects on populations, and finally altered community metrics, all presumably resulting from exposure to chemical contaminants in the habitat of the affected species. Each of these case study papers evaluates the strength of possible causal relationships using the same seven standard criteria. Following the case study papers, the next two presentations represent efforts by a Canadian and an American group to expand our thinking on causal relationships by setting up a tiered approach for focusing down on causality, and pointing out possible sources of errors in establishing causality. As an alternative approach to establishing possible causal relationships in field situations, the next to last paper in this series presents the use of nested models and how they can be used to extrapolate laboratory studies to effects at the population level. Finally, an overview paper provides an integration relative to how the seven causal criteria were used by the different research groups, and makes recommendations for further modifications to criteria and approaches for establishing causality in terrestrial and aquatic ecosystems.