The WET test is a method that evaluates toxicity, including multiple effects,
because it is targeted at test waters containing multiple chemical substances rather
than being used for evaluations of the toxicity of individual chemical substances.
However, although we use individual species (fish, crustaceans, and algae) located in
different niches in the food chain for the assay, it is a single-species test only. It is not
a test method that accounts for material cycles, energy flow, or biological interactions, which are the basic elements of natural ecosystems. The microcosm is a
system that includes multiple species in coexistence and contains material circulation, energy flow, and biological interactions. Therefore, the microcosm makes it
possible to evaluate the risks associated with added chemical substances at the
ecosystem level. The safety factors for the ecological effects of chemical substances
obtained by the microcosm test were supported by the high correlation observed
between the microcosm test and mesocosm (natural ecosystem) test obtained from
the Environmental Research Comprehensive Promotion Fund (2009–2011) and the
New LRI (2012–2014). Therefore, we determined that it is possible to use the
microcosm test to evaluate the effects of chemical substances in an ecosystem with
higher precision and with less dispersion than in the conventional single-species
tests, such as the HC5 method. Consequently, it is possible to calculate more realistic
values of the PNOEC for natural ecosystems using the microcosm.
Microcosms are highly correlated with natural ecosystems and can be regarded as
models containing the basic components and characterized by the basic principles of
natural ecosystems. From this fact, it is considered that a more realistic estimate of
the NOEC can be obtained using a microcosm as compared with the current singlespecies test that does not account for material cycling, energy flow, or biological
interactions. In the ecosystem impact assessment of wastewater containing various
chemical substances, comprehensive tests were conducted to introduce the ecosystem model, a multiple-species test with a food chain and energy flow, simultaneously
with the single-species test. A series of test methods were constructed, making it
possible to evaluate the degradability and persistence of chemical substances
contained in wastewater and the collapse and restoration of ecosystem functions.
The microcosm test can be performed at a lower cost than the WET test with
commonly used single species (fishes, crustaceans, and algae). The microcosm has
already been subcultured for nearly 40 years and is easy to use by researchers
accustomed to environmental microorganism testing who can master the microbial
culturing procedures. It is also easy to use after short-term training. Additionally, a
series of tests are possible without using expensive culturing tools or measurement
instruments.
The position of the microcosm test within the WET test is shown in Fig. 9.1. The
foundation of a certain ECETOC method and the HC5 method conventionally
includes the evaluation of independent chemical substances in toxicity tests using
single species, and the current WET test also uses single species for toxicity tests on
the composition of chemical substances. The interactions between species constitute
the ecosystem and drive the cycling of materials and energy flow; no single species is
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because it is targeted at test waters containing multiple chemical substances rather
than being used for evaluations of the toxicity of individual chemical substances.
However, although we use individual species (fish, crustaceans, and algae) located in
different niches in the food chain for the assay, it is a single-species test only. It is not
a test method that accounts for material cycles, energy flow, or biological interactions, which are the basic elements of natural ecosystems. The microcosm is a
system that includes multiple species in coexistence and contains material circulation, energy flow, and biological interactions. Therefore, the microcosm makes it
possible to evaluate the risks associated with added chemical substances at the
ecosystem level. The safety factors for the ecological effects of chemical substances
obtained by the microcosm test were supported by the high correlation observed
between the microcosm test and mesocosm (natural ecosystem) test obtained from
the Environmental Research Comprehensive Promotion Fund (2009–2011) and the
New LRI (2012–2014). Therefore, we determined that it is possible to use the
microcosm test to evaluate the effects of chemical substances in an ecosystem with
higher precision and with less dispersion than in the conventional single-species
tests, such as the HC5 method. Consequently, it is possible to calculate more realistic
values of the PNOEC for natural ecosystems using the microcosm.
Microcosms are highly correlated with natural ecosystems and can be regarded as
models containing the basic components and characterized by the basic principles of
natural ecosystems. From this fact, it is considered that a more realistic estimate of
the NOEC can be obtained using a microcosm as compared with the current singlespecies test that does not account for material cycling, energy flow, or biological
interactions. In the ecosystem impact assessment of wastewater containing various
chemical substances, comprehensive tests were conducted to introduce the ecosystem model, a multiple-species test with a food chain and energy flow, simultaneously
with the single-species test. A series of test methods were constructed, making it
possible to evaluate the degradability and persistence of chemical substances
contained in wastewater and the collapse and restoration of ecosystem functions.
The microcosm test can be performed at a lower cost than the WET test with
commonly used single species (fishes, crustaceans, and algae). The microcosm has
already been subcultured for nearly 40 years and is easy to use by researchers
accustomed to environmental microorganism testing who can master the microbial
culturing procedures. It is also easy to use after short-term training. Additionally, a
series of tests are possible without using expensive culturing tools or measurement
instruments.
The position of the microcosm test within the WET test is shown in Fig. 9.1. The
foundation of a certain ECETOC method and the HC5 method conventionally
includes the evaluation of independent chemical substances in toxicity tests using
single species, and the current WET test also uses single species for toxicity tests on
the composition of chemical substances. The interactions between species constitute
the ecosystem and drive the cycling of materials and energy flow; no single species is
168
Y. Inamori et al.