The theory of microcosm and its application in ecotoxicology

Microcosms,generally including mesocosms,are small experimental ecosystems or model e- cosystems.In recent years,microcosms have been widely used in ecological field.“Biosphere2”,a huge microcosm even including human within,was constructed in 1 986 in USA for study of the Earth ecosys- tem.Microcosms have played an important role in protecting the Earth eco- environment.Microcosms are also useful methods in ecotoxicological research because they provide a possibility to study the effects of pollutants on the ecosystems under artificially controlled conditions.This paper emphasized the application of microcosms in ecotoxicology. The concept of microcosm originated from philosophic field in ancient Greeks.Itmeans that portions varying in size of the world exhibit similarities in structures and functions,and one portion imitates anoth- er or others atdifferentlevels. Such analogy extrapolation was refereed in philosophy as microcosm theo- ry.Although in the middle of nineteenth century Warrington published the first scientific paper on micro- cosms,until the first of century 2 0 microcosmic thought did not shifted really from philosophy to natural sciences,especially ecological science.In1 970 ' s microcosms drew attention in ecotoxicology as its develop- ment. Metcalf was the first to use microcosms in the studies of the fate of insecticides and some toxic sub- stances in ecosystems.In1 980 ,Giesy and Odum introduced the microcosmology.Recently,the Chinese scientists have widely applied microcosms into ecotoxicological research. Microcosms are generally divided into three kinds,namely terrestrial,wetland and aquatic micro- cosms.Relatively satisfactory terrestrial microcosms were‘farm pond' used by Metcalf to testthe toxicity of pesticides,food additives and industrial chemicals. However,since terrestrial microcosms have limited test animals and longer turnover period,itis difficult to get statistic data of toxicity,such as L D50 value. Wetland microcosms are suitable for studies of pesticide residues in wetland systems and treatment of pol- lutants by wetland systems.Aquatic microcosms have been studied popularly much and developed more perfectly.Various types of microcosms simulating river,lake,estuary and marine ecosystems have been developed.Aquaria are the firstof microcosms,and they can be simply constructed and controlled.Proba- bly millions of these microcosms have been setup around the world,however few were seriously studied. Stream microcosms include channel and circulating microcosms. In particular,circulating microcosms have compact structures and they occupied small area,they are useful for the environmental hazard assessment of chemicals though they have poorreality.Pond and pool microcosms have been widely used to investigate the processes of silf- organization including eutrophication and ecotoxicological effects of pollutants.Thy may be useful facilities for the tests of the environmental risk assessment at middle or higher levels.En- closed column microcosms include enclosures in lakes and oceans.They are realistic,but cost expensive and they are difficultto operate fora long time.Land- based marine microcosms simulate marine orestuary ecosystems. They can operate for a longer time than enclosures in oceans (e.g. pelagic marine microcosms) ,but they need a longer turnover time to reach a stable state.Reef and benthic microcosms are significant for protecting biodiversity. Ecological microcosms provide an important tool to research on ecological effects of toxic pollutants and the response of ecosystems to pollutants atecosystem levels.They have been used to trace the distri- bution in space and time,the transfers and the transformations of pollutants labeled with radioactive trac- ers and their metabolites.Institute of Zoology,Chinese Academy of Sciences(CAS) set up pond micro- cosms in theirlaboratory and pond mesocosms forresearch ofthe effects of pesticides on the structures and functions of ecosystems.They drew the conclusions as following:All these microcosm