cultivation period were 10% or less (50 independent experiments). This value is
almost the same as previously reported values (e.g., Inamori et al. 1992; Kurihara
1978a, b).
From these outcomes, the effects of Mg and Ca on the aquatic ecosystem as
sediment remediation materials both indicate powerful nutrient removal (especially
for phosphorus) by bonding with PO 4 -P through chemisorption in the water eluted
from the eutrophied sediment (Murakami et al. 2000), differing in both influential
concentrations and target microorganisms. The impact risk to the aquatic ecosystem of
Mg was estimated as half that of Ca from the viewpoint of the concentration that had
any influence on the microorganisms in the microcosm. The m-NOEC was estimated
to be less than or equal to 10.0 mg/L for Mg and as less than or equal to 5.0 mg/L for
Ca, from the viewpoint of changes in the P/R ratio, which is considered to be the
functional parameter of the microcosm. From the biotic succession, as the structural
parameter, the m-NOEC was considered to be less than or equal to 5.0 mg/L for Mg
and much lower than 5.0 mg/L for Ca, with the abundance of protozoans, rotifers, and
oligochaetes obviously decreasing and not recovering. However, the P/R ratio of the
microcosm was maintained at the value of 1, notwithstanding the different biota,
which consisted of producers, consumers, and decomposers, as the basic components
of the ecosystem. Considering that the P/R ratio of the natural ecosystem in the stable
state converges to almost 1 (Odum 1983), the m-NOEC should be estimated by the
P/R ratio (functional parameter) rather than by the biotic succession (structural
parameter). Further discussion and experimental data are necessary to better understand this estimation method.
7.10.8 Ni
Nickel is used for alloying and plating, and it may become mixed with tap water by
elution from mine wastewater and nickel plating. The toxicity of Ni is different from
a chemical form in the properties of matter; the oral toxicity is relatively low and is at
the same level as the requisiteness of other metals, such as Cu, Co, and Zn, but the
toxicity of inhaled nickel carbonyl is high, and the fatal dose for Homo sapiens has
been estimated as 30 ppm/30 min. For Ni and its compounds, the targeted value for
water quality management is less than 0.01 mg/L (temporarily).
Nickel was supplied for assessment, and the no-addition system (control) and
addition systems (0.1, 1.0, 5.0, and 10 mg/L) were adjusted and added 16 days after
culturing began. 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).
120
K. Murakami et al.
almost the same as previously reported values (e.g., Inamori et al. 1992; Kurihara
1978a, b).
From these outcomes, the effects of Mg and Ca on the aquatic ecosystem as
sediment remediation materials both indicate powerful nutrient removal (especially
for phosphorus) by bonding with PO 4 -P through chemisorption in the water eluted
from the eutrophied sediment (Murakami et al. 2000), differing in both influential
concentrations and target microorganisms. The impact risk to the aquatic ecosystem of
Mg was estimated as half that of Ca from the viewpoint of the concentration that had
any influence on the microorganisms in the microcosm. The m-NOEC was estimated
to be less than or equal to 10.0 mg/L for Mg and as less than or equal to 5.0 mg/L for
Ca, from the viewpoint of changes in the P/R ratio, which is considered to be the
functional parameter of the microcosm. From the biotic succession, as the structural
parameter, the m-NOEC was considered to be less than or equal to 5.0 mg/L for Mg
and much lower than 5.0 mg/L for Ca, with the abundance of protozoans, rotifers, and
oligochaetes obviously decreasing and not recovering. However, the P/R ratio of the
microcosm was maintained at the value of 1, notwithstanding the different biota,
which consisted of producers, consumers, and decomposers, as the basic components
of the ecosystem. Considering that the P/R ratio of the natural ecosystem in the stable
state converges to almost 1 (Odum 1983), the m-NOEC should be estimated by the
P/R ratio (functional parameter) rather than by the biotic succession (structural
parameter). Further discussion and experimental data are necessary to better understand this estimation method.
7.10.8 Ni
Nickel is used for alloying and plating, and it may become mixed with tap water by
elution from mine wastewater and nickel plating. The toxicity of Ni is different from
a chemical form in the properties of matter; the oral toxicity is relatively low and is at
the same level as the requisiteness of other metals, such as Cu, Co, and Zn, but the
toxicity of inhaled nickel carbonyl is high, and the fatal dose for Homo sapiens has
been estimated as 30 ppm/30 min. For Ni and its compounds, the targeted value for
water quality management is less than 0.01 mg/L (temporarily).
Nickel was supplied for assessment, and the no-addition system (control) and
addition systems (0.1, 1.0, 5.0, and 10 mg/L) were adjusted and added 16 days after
culturing began. 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).
120
K. Murakami et al.