Assessing the Ecological Risk of Chemicals in the Japanese Aquatic Environment. K. Miyamoto and S. Masunaga, National Institute of Materials and Chemical Research, 1-1 Higashi, Tsukuba, Ibaraki 305, Japan; J. Nakanishi, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240, Japan; and S. M. Bartell, SENES Oak Ridge, Inc., 102 Donner Drive, Oak Ridge, TN 37830
In an attempt to quantify the potential dangers of chemicals to ecosystems, numerous toxicity tests have been developed. The majority of these tests are performed using a single species under fixed conditions. This paper presents a method for evaluating the potential risk posed by chemicals to aquatic ecosystems in Japan and applications of this method. The Comprehensive Aquatic Simulation Model (CASM) is used to simulate population dynamics, including predator-prey interactions, under time-varying environmental conditions from the results of laboratory toxicity tests using a single species. The epilimnion of the modeled ecosystem in the CASM includes one bacterial population, 10 phytoplankton populations, 5 zooplankton populations, 3 populations of forage fish, and a single piscivorous fish population. The hypolimnion includes one bacterial population, 2 populations of benthic insects, 3 populations of benthic invertebrates, 3 populations of omnivorous fish and a single piscivorous fish population. The littoral subsystem includes 5 macrophyte populations and 5 periphyton populations. The biomass of primary producers is calculated using equations describing physiological processes such as photosynthesis, grazing, non-predatory death, respiration, and so on. For consumer populations, consumption, egestion, non-predatory death, respiration, et. are considered. Changes in such processes due to exposure to toxic chemical are calculated by simulating bioassay results using similar equations to describe the above physiological processes. The risks posed by chemicals are calculated as probabilities of the decrease in biomass using Monte Carlo simulations. The simulated biomass under no toxic stress was compared with the field observed biomass for species in Lake Biwa and relatively good agreement was observed between the two. One of the important results obtained using this method was that certain chemicals, such as pentachlorophenol, might decrease the biomass of insensitive species when their prey populations decrease in number, or their predator populations increase as a result of the effects of the chemicals.
Work supported by CREST (Core Research for Evolutional Science and Technology) of Japan Science and Technology Corporation (JST).