it will be established as a public, fixed method and could have wide utility after
validation by other institutions and peer review (international examination). Furthermore, by following the WET test method and utilizing the results provided by
this project to their maximum, it is expected this technique will provide new
environmental policy information from Japan for development as an international,
standardized OECD test.
In the optimized microcosm, producers, predators, and decomposers are properly
structured, and they can be used for highly accurate environmental impact assessments. It can be said that the optimized microcosm test system is not the current
OECD test method for individual organisms, such as Daphnia or algae, utilized for
the WET test, but a test system that approximates natural ecosystems as closely as
possible. Therefore, more realistic results at the ecosystem level are expected to be
obtained by using the microcosm test method. In order to determine the standard of
treated water quality in wastewater treatment, it is important to consider how the
trace substances in the treated water affect the aquatic ecosystem at the discharge
destination. Also, in promoting environmental impact assessment, it is necessary to
evaluate various chemical substances that may affect aquatic ecosystems. According
to the OECD test method, representative species are selected one by one from each
trophic level of the ecosystem (e.g., Selenastrum (producer), Ceriodaphnia (primary
predator), Danio rerio (higher predator), luminescent bacteria (decomposers), etc.),
toxicity assessments are then performed, and then the ecosystem impact is calculated
based on the toxicity data for the most sensitive species. However, in natural
ecosystems, the biological activity of test organisms is different from that of
single-species tests because there are biological interactions, material circulation,
and energy flows in natural ecosystems. Therefore, toxicity assessments under
different biological active conditions are insufficient, particularly as impact assessments of ecosystem function. For this reason, it has been noted that the OECD
should conduct various biological tests. It is very important to develop an evaluation
tool from aquatic ecosystem models (Takamatsu et al. 1995). To evaluate the
toxicity of chemical substances to ecosystems with complex biological interactions,
microcosms of model ecosystems composed of producers (algae), predators
(microanimals), and decomposers (bacteria) are useful tools. Whole aquatic ecosystems are composed of food webs (i.e., biological interactions, including high-order
predators, such as fish), based on microbial loops that are mainly composed of
microbes. To evaluate the effect of chemical loads on complex ecosystems, it is
important to consider multiple parameters, including the production (P)/respiration
(R) ratio. Establishing risk management methods for ecosystems based on environmental changes and the analyzed relationships between the microbial organisms and
higher predators that constitute aquatic ecosystems becomes very important
(Fig. 10.1). For ecosystem impact assessments, it is effective to comprehensively
utilize the kinetic analysis of microbial communities using the microcosm and other
multi-species mixed model ecosystems (stable model ecosystems).
This research was conducted to establish a standard test method characterized by
both high plasticity and low cost using the microcosm that has been stably
subcultured for more than 40 years. The basic manual that affected the testing
12 Further Perspectives
211
validation by other institutions and peer review (international examination). Furthermore, by following the WET test method and utilizing the results provided by
this project to their maximum, it is expected this technique will provide new
environmental policy information from Japan for development as an international,
standardized OECD test.
In the optimized microcosm, producers, predators, and decomposers are properly
structured, and they can be used for highly accurate environmental impact assessments. It can be said that the optimized microcosm test system is not the current
OECD test method for individual organisms, such as Daphnia or algae, utilized for
the WET test, but a test system that approximates natural ecosystems as closely as
possible. Therefore, more realistic results at the ecosystem level are expected to be
obtained by using the microcosm test method. In order to determine the standard of
treated water quality in wastewater treatment, it is important to consider how the
trace substances in the treated water affect the aquatic ecosystem at the discharge
destination. Also, in promoting environmental impact assessment, it is necessary to
evaluate various chemical substances that may affect aquatic ecosystems. According
to the OECD test method, representative species are selected one by one from each
trophic level of the ecosystem (e.g., Selenastrum (producer), Ceriodaphnia (primary
predator), Danio rerio (higher predator), luminescent bacteria (decomposers), etc.),
toxicity assessments are then performed, and then the ecosystem impact is calculated
based on the toxicity data for the most sensitive species. However, in natural
ecosystems, the biological activity of test organisms is different from that of
single-species tests because there are biological interactions, material circulation,
and energy flows in natural ecosystems. Therefore, toxicity assessments under
different biological active conditions are insufficient, particularly as impact assessments of ecosystem function. For this reason, it has been noted that the OECD
should conduct various biological tests. It is very important to develop an evaluation
tool from aquatic ecosystem models (Takamatsu et al. 1995). To evaluate the
toxicity of chemical substances to ecosystems with complex biological interactions,
microcosms of model ecosystems composed of producers (algae), predators
(microanimals), and decomposers (bacteria) are useful tools. Whole aquatic ecosystems are composed of food webs (i.e., biological interactions, including high-order
predators, such as fish), based on microbial loops that are mainly composed of
microbes. To evaluate the effect of chemical loads on complex ecosystems, it is
important to consider multiple parameters, including the production (P)/respiration
(R) ratio. Establishing risk management methods for ecosystems based on environmental changes and the analyzed relationships between the microbial organisms and
higher predators that constitute aquatic ecosystems becomes very important
(Fig. 10.1). For ecosystem impact assessments, it is effective to comprehensively
utilize the kinetic analysis of microbial communities using the microcosm and other
multi-species mixed model ecosystems (stable model ecosystems).
This research was conducted to establish a standard test method characterized by
both high plasticity and low cost using the microcosm that has been stably
subcultured for more than 40 years. The basic manual that affected the testing
12 Further Perspectives
211