Effects of Chemicals and Metal Ions on Microcosms: Comparison of Community Metabolism to Single-Species Responses to Toxicants

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Eleven organic compounds, including insecticides, herbicides, surfactants, and general organic compounds, and three metal ions were added to an aquatic model ecosystem (microcosm) comprising two photosynthetic organisms (Chlorella and Schizothrix), a protozoan (Cyclidium), two rotifers (Philodina and Lepadella), a worm (Aeolosoma), and at least 5 types of bacteria. The observed maximum concentrations of the substances having no effects on the respiration rate and the production rate in the microcosm at the mature stage (m-NOAECs) were determined. The m-NOAECs were compared with the predicted no-effect concentrations in the ecosystems (PNECs) that were estimated from the no-observed-effect concentrations of the substances in a single-species. There were significant differences in some of substances between the PNECs and the m-NOAECs. When the sensitivities to the substances were compared between the consumers and the producers, in the cases of the substances having higher sensitivity to the producers, the differences between the PNECs and the m-NOAECs were small; however, in the cases of the substances having higher sensitivity to the consumers, the PNECs were consistently lower than the m-NOAECs. The reason for the differences was discussed based on the calculated results using a mathematical model.