Guest ▼Comment Ecotoxicology—A multidisciplinary, problem-driven science his special issue of ES&T is focused on ecotoxicology. What is ecotoxicology? It is a multidisciplinary scientific endeavor that, unlike some areas of science, is most often problem-driven. Ecotoxicological research seeks to assist society by providing knowledge and understanding of the adverse effects of chemicals on our environment. Aspects of ecotoxicology encompass a daunting array of chemicals, species (and associated end points), and systems. The ultimate goal is to understand how chemical stressor(s) might affect organisms (and assemblages) at individual, population, community, and even ecosystem levels. This is, of course, complicated by the fact that chemicals don’t act in isolation but interact with a host of other physical and biological stressors (e.g., UV radiation, temperature, pathogens, exotic species), as well as changes in habitat, in contributing to small-scale and global ecosystem effects. Mechanism- and process-oriented studies are critical to ecotoxicology, providing detailed insights (e.g., at the molecular level) that form the basis for extrapolation across chemicals, species, and, ultimately, ecosystems. Although important, mechanistic studies themselves do not suffice. For example, Alexander Zehnder concluded in his Comment on ecotoxicology that “to fully understand a given system and its responses to disturbances, the different levels combined with their intraspecies interactions need to be studied” (1). We can draw an analogy with the more chemistry-oriented topic of chemical sorption to soil particles—studying the interactions of chemicals with mineral surfaces or organic matter is not sufficient, because we also need to know something about the interactions between the mineral and organic matter to fully understand the chemical’s connection with a soil particle. In ecotoxicology, numerous types of interactions may occur. Therefore, there is a need for a better understanding of the interactions, not only among different organisms (2), but also among the various stressors and other conditions in the environment that may influence chemical effects (e.g., alterations in bioavailability). At the other end of the size spectrum, field studies are also critical to ecotoxicology. Standard laboratory studies are not always sufficient to identify and quantify the potential ecological risk of chemical stressors. The no-observed-effect concentration (NOEC) is a frequently used measure derived from lab studies designed to support ecological risk assessments. The term “observed” is an essential element in the NOEC, in that we cannot predict effects if we don’t know to look for them. The present attention given to xenoestrogens is a case in point. The discovery of these compounds arose from observations of sexual disruption of wild fish (3). As a re-
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sult, test protocols have been designed and implemented to define NOECs in terms of estrogenicity. But it is a virtual certainty that other effects are occurring in the field that we are presently overlooking in the lab. Hence, a challenge for ecotoxicologists is the development of explorative methods and approaches that enable broader screening for adverse responses. Emerging developments in gene and protein expression profiling may serve as a foundation for this type of exploration. Nico van Straalen recently introduced the term “stress ecology” and predicted that ecotoxicogenomics would provide the basis for new insights into ecological risk assessments for chemicals (4). A major challenge in this area will be linking changes in gene and protein expression to adverse outcomes in individuals and, subsequently, populations exposed to combinations of stressors (5). However, ecotoxicologists face an even more demanding challenge: How can all biodiversity be protected from the myriad of chemicals they are now exposed to, when we know relatively little about real-world exposures and even less about the flora and fauna we want to protect? If we do not even know what is there—and in many parts of the world we know very little (6)—how can we possibly know what we need to protect, let alone actually protect it from the many chemicals that now pollute the earth? To us, this is the ultimate challenge in ecotoxicology. Protecting fish in English, Dutch, or American rivers is one thing (albeit not an easy task!), but protecting all those unidentified species of fish, frogs, and everything else in less well studied locations is quite another level of challenge. Yet, it is one we must all rise to. Ecotoxicology is not a “luxury” research area, undertaken only in rich countries. It is relevant and important to all countries and all habitats, and it is vital if we are to protect our living heritage from the cocktail of chemicals present in all environments. In this issue, we bring together a series of articles on challenging issues in ecotoxicology. A key element is a focus on a mechanistic understanding of toxic effects as well as interactions among stressors at multiple biological levels of organization. These papers also serve to highlight the multidisciplinary nature of ecotoxicology. We have grouped the publications around the following themes: mechanisms of effect, exposure and bioaccumulation, multiple stressors, and field-oriented studies. The mechanism-oriented articles present detailed insights into how effects of different classes of chemicals are initiated at the molecular level, resulting in adverse outcomes in the whole animal. Several papers describe novel pathways through which reproduction and development in animals can be affected. Other papers illustrate how an understanding of mechanism serves as the © 2004 American Chemical Society
basis for test design and validation as well as for extrapolation across species, and, through the use of modeling approaches, across chemical structures. This special ES&T issue also focuses on exposure to chemical contaminants. Quantifying exposure is an essential aspect of (eco)toxicology; to achieve this, it is critical to understand chemical interactions. As described in several papers, bioavailability and accumulation of contaminants are influenced by interactions with abiotic as well as biotic components of the environment. Modeling these phenomena is essential for developing sound ecological risk assessments. Other manuscripts describe the development of better testing systems from an exposure perspective and tools to more accurately measure exposure in toxicity tests. Another area where interactions are of great importance is multiple stressors, chemical as well as nonchemical. We are almost always exposed to complex chemical mixtures in the environment, yet most risk assessments are based on single-chemical approaches. Further, the situation is even more complex when the effects of chemicals
are modified or enhanced by the presence of other, nonchemical stressors. Several papers address mixtures of stressors, from both a modeling and an experimental perspective. The last group of publications deals with studies in the field (including mesocosms) or with effects of samples taken directly from the field. Because of the difficulty and expense of high-quality field-oriented studies, this type of research is often neglected. Yet, field studies are the ultimate “ground truthing” for predictions made from laboratory experiments and models. Field-oriented studies are also crucial when they point to unanticipated adverse effects and/or classes of contaminants. We realize that it is impossible to adequately cover the whole field of ecotoxicology in one issue of a journal, but we feel that these various papers highlight several critical and new areas of research as well as recent advances in the field. We also hope that the studies described in this issue serve to highlight the importance of interactions between multiple disciplines, including environmental chemistry and toxicology, when ecotoxicology
research is conducted. In closing, we would like to thank the authors and reviewers for their efforts and timely responses. Finally, we would like to acknowledge the very efficient assistance of Anke Schaefer, Marie-Jeanne Weyrich, and Barbara Booth (ES&T office staff) and Rachel Petkewich and Alan Newman (magazine staff).
References (1) Zehnder, A. J. B. Environ. Sci. Technol. 2003, 37, 199A. (2) Calow, P.; Forbes, V. E. Environ. Sci. Technol. 2003, 37, 146A–151A. (3) Jobling, S.; Nolan, M.; Tyler, C. R.; Brighty, G.; Sumpter, J. P. Environ. Sci. Technol. 1998, 32, 2498–2506. (4) van Straalen, N. Environ. Sci. Technol. 2003, 37, 324A–330A. (5) Renner, R. Environ. Sci. Technol. 2004, 38, 303A–304A. (6) Editorial, Nature 2004, 430, 385.
Joop L. M. Hermens, Utrecht University, The Netherlands Gerald T. Ankley, U.S. EPA MidContinent Ecology Division, Duluth, Minn., United States John P. Sumpter, Brunel University, United Kingdom
Guest editors for the Ecotoxicology Special Issue Three editors selected manuscripts for consideration and managed the review process for the papers in this issue of ES&T.
Joop L. M. Hermens Utrecht University (The Netherlands) Special Issue Editor
Gerald T. Ankley U.S. EPA Mid-Continent Ecology Division
John P. Sumpter Brunel University (U.K.)
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