As the result of the gnotobiotic-type microcosm test (N-system), after evaluating
the ecosystem risk from the change in the P/R ratio as the functional parameter, no
influence was observed at 0.1 mg/L of Ni addition, but respiration increased with
1.0 mg/L of addition, and the P/R ratio was greater than 1. From this, it was thought
that Ni acted to increase the amount of respiration in the system. Microbiota in the
microcosm were divided into two groups, those of increased abundance (microalgae)
and those of decreased abundance (microanimals) in comparison with the control
system, using the abundance as the structural parameter. The respiration activity per
microanimal population rose, and the production activity per microalgae decreased
with an increasing concentration of Ni, based on the evaluation of changes in the DO
concentration per individual, because B 16–30 revealed a decrease in the microanimal
population with the addition of Ni.
From these outcomes, the m-NOEC of Ni was estimated to be between 0.1 and
1.0 mg/L. Additionally, as the result of the naturally derived microcosm test, the P/R
ratio (functional parameter) converged to approximately 1, but the microbiota in the
control (no-addition system) were not stable, and the abundance of organisms
(structural parameter) also differed. Reproducibility was not maintained in all of
the systems. During the culture period, Chlorella sp., Nitzschia sp., Monoraphidium
contortum, and Aulacoseira granulata ordinarily appeared, but no characteristic
behavior linked to Ni addition was observed. As the result of the stress-selectedtype microcosm test, only 7 stable systems out of the 40 total systems were
established. Even in the control system, the reproducible stability was insufficient.
No remarkable change was observed, regardless of the concentration of the Ni
addition, and the P/R ratio varied near 1 and was stable. However, a clear decrease
in population occurred at a 1.0 mg/L concentration of Ni, and it was shown that
Nitzschia sp. and Monoraphidium contortum were particularly affected. It was
predicted that diatomaceans were affected more than chlorophyceans.
7.10.9 Co
Cobalt was supplied for impact assessment to the no-addition system (control) and
addition systems (1, 1.5, 2, 4, 6, 8, and 10 mg/L concentrations) and was added
16 days after the start of culturing. The endpoints were abundance (structural
parameter) and the concentration of DO (functional parameter), and the population
was measured using an optical microscope and counted from the start of culturing on
days 0, 2, 4, 7, 14, 16, 18, 20, 23, and 30; it was evaluated from the results of B 16–30
(days 16–30), which was the ratio of abundance and population density (N 30 ) on the
30th day. The DO concentration was measured continuously from the 16th day, and
the P/R ratio was calculated from the amounts of production (P) and respiration (R).
As a structural parameter, the acute influence B 16–20 (0–4 days after loading),
subacute influence B 20–23 (5–7 days after loading), chronic influence B 23–30
(8–14 days after loading), and B 16–30 as abundance were estimated. As a result,
microorganisms did not perish during the period of acute influence, but extinction
7 Example Assessments of the Microcosm N-System
121
the ecosystem risk from the change in the P/R ratio as the functional parameter, no
influence was observed at 0.1 mg/L of Ni addition, but respiration increased with
1.0 mg/L of addition, and the P/R ratio was greater than 1. From this, it was thought
that Ni acted to increase the amount of respiration in the system. Microbiota in the
microcosm were divided into two groups, those of increased abundance (microalgae)
and those of decreased abundance (microanimals) in comparison with the control
system, using the abundance as the structural parameter. The respiration activity per
microanimal population rose, and the production activity per microalgae decreased
with an increasing concentration of Ni, based on the evaluation of changes in the DO
concentration per individual, because B 16–30 revealed a decrease in the microanimal
population with the addition of Ni.
From these outcomes, the m-NOEC of Ni was estimated to be between 0.1 and
1.0 mg/L. Additionally, as the result of the naturally derived microcosm test, the P/R
ratio (functional parameter) converged to approximately 1, but the microbiota in the
control (no-addition system) were not stable, and the abundance of organisms
(structural parameter) also differed. Reproducibility was not maintained in all of
the systems. During the culture period, Chlorella sp., Nitzschia sp., Monoraphidium
contortum, and Aulacoseira granulata ordinarily appeared, but no characteristic
behavior linked to Ni addition was observed. As the result of the stress-selectedtype microcosm test, only 7 stable systems out of the 40 total systems were
established. Even in the control system, the reproducible stability was insufficient.
No remarkable change was observed, regardless of the concentration of the Ni
addition, and the P/R ratio varied near 1 and was stable. However, a clear decrease
in population occurred at a 1.0 mg/L concentration of Ni, and it was shown that
Nitzschia sp. and Monoraphidium contortum were particularly affected. It was
predicted that diatomaceans were affected more than chlorophyceans.
7.10.9 Co
Cobalt was supplied for impact assessment to the no-addition system (control) and
addition systems (1, 1.5, 2, 4, 6, 8, and 10 mg/L concentrations) and was added
16 days after the start of culturing. The endpoints were abundance (structural
parameter) and the concentration of DO (functional parameter), and the population
was measured using an optical microscope and counted from the start of culturing on
days 0, 2, 4, 7, 14, 16, 18, 20, 23, and 30; it was evaluated from the results of B 16–30
(days 16–30), which was the ratio of abundance and population density (N 30 ) on the
30th day. The DO concentration was measured continuously from the 16th day, and
the P/R ratio was calculated from the amounts of production (P) and respiration (R).
As a structural parameter, the acute influence B 16–20 (0–4 days after loading),
subacute influence B 20–23 (5–7 days after loading), chronic influence B 23–30
(8–14 days after loading), and B 16–30 as abundance were estimated. As a result,
microorganisms did not perish during the period of acute influence, but extinction
7 Example Assessments of the Microcosm N-System
121