exposed to unpredictable environmental factors. Instead of working with a natural
ecosystem, it is convenient to use microcosms consisting of biotic and abiotic factors
that originated from a natural ecosystem because they allow for both biological
simplicity and replication (Beyers 1963; Cook 1967; Margalef 1969; Kawabata et al.
1978). In this section, the effects of surfactants on the aquatic ecosystem and the
biodegradability of surfactants are described.
7.1.1 Linear Alkylbenzene Sulfonate (LAS)
A microcosm was used to assess the effects of the anionic surfactant, linear
alkylbenzene sulfonate (LAS), on an aquatic ecosystem. The addition concentration
of LAS was adjusted to 1, 5, and 10 mg/L and was added on the 16th day of the
stable state into the microcosm. Linear alkylbenzene sulfonate supplied to this
experiment was composed of a sodium linear-dodecyl benzene sulfonate standard
(C12) and LAS at a purity of more than 99%.
The endpoints were the population density (structural parameter) and DO (functional parameter), and the population was measured by an optical microscope and
counted from the beginning of culturing on days 0, 2, 4, 7, 14, 16, 18, 20, 23, and
30, and it was evaluated from the results of B16–30 (days 16–30), which was the
ratio of the abundance and population density (N 30 ) on the 30th day. The DO was
measured continuously from the 16th day onward, and the P/R ratio was calculated
from the amounts of production (P) and respiration (R). Using the structural parameter, the impact of LAS was evaluated in comparison with the control system
according to the behaviors of the microorganisms in the microcosm on each of the
14 days after the addition of LAS for which measurements were taken. The population that did not change relative to the control system was maintained at a 1 mg/L
surfactant load and recovered to almost the same population density, while there was
a decrease in the density of microanimals in the microcosm with the 5 mg/L load. In
the microcosm with a 10 mg/L load of LAS, Cyclidium glaucoma and Philodina
erythrophthalma disappeared, and the populations of Lecane sp., Aeolosoma
hemprichi, and Tolypothrix sp. were stable at low densities, and the microcosm
ecosystem did not collapse.
As a result of the observed changes in the structural parameter, the m-NOEC
(microcosm maximum effect-free concentration) of LAS was estimated as 1 mg/L.
While the NOEC of LAS for Daphnia magna in a single-species examination was
1180–3250 μg/L and the NOEC for algae was 400–18,000 μg/L, it was thought that
the m-NOEC exhibited slight unevenness. It was shown that the evaluations of the
microcosm test using the structural parameter (i.e., population density) and the
functional parameter (i.e., the P/R ratio) were consistent. The microcosm test is an
effective tool for assessing the effects of surfactants on ecosystems because it allows
for the evaluation of the effects of surfactants from the viewpoint of the interactions
among microorganisms, material cycling, and energy flow. Based on these characteristics, the microcosm test is a useful method of performing environmental assessments that can reflect the behavior of natural aquatic ecosystems.
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K. Murakami et al.
ecosystem, it is convenient to use microcosms consisting of biotic and abiotic factors
that originated from a natural ecosystem because they allow for both biological
simplicity and replication (Beyers 1963; Cook 1967; Margalef 1969; Kawabata et al.
1978). In this section, the effects of surfactants on the aquatic ecosystem and the
biodegradability of surfactants are described.
7.1.1 Linear Alkylbenzene Sulfonate (LAS)
A microcosm was used to assess the effects of the anionic surfactant, linear
alkylbenzene sulfonate (LAS), on an aquatic ecosystem. The addition concentration
of LAS was adjusted to 1, 5, and 10 mg/L and was added on the 16th day of the
stable state into the microcosm. Linear alkylbenzene sulfonate supplied to this
experiment was composed of a sodium linear-dodecyl benzene sulfonate standard
(C12) and LAS at a purity of more than 99%.
The endpoints were the population density (structural parameter) and DO (functional parameter), and the population was measured by an optical microscope and
counted from the beginning of culturing on days 0, 2, 4, 7, 14, 16, 18, 20, 23, and
30, and it was evaluated from the results of B16–30 (days 16–30), which was the
ratio of the abundance and population density (N 30 ) on the 30th day. The DO was
measured continuously from the 16th day onward, and the P/R ratio was calculated
from the amounts of production (P) and respiration (R). Using the structural parameter, the impact of LAS was evaluated in comparison with the control system
according to the behaviors of the microorganisms in the microcosm on each of the
14 days after the addition of LAS for which measurements were taken. The population that did not change relative to the control system was maintained at a 1 mg/L
surfactant load and recovered to almost the same population density, while there was
a decrease in the density of microanimals in the microcosm with the 5 mg/L load. In
the microcosm with a 10 mg/L load of LAS, Cyclidium glaucoma and Philodina
erythrophthalma disappeared, and the populations of Lecane sp., Aeolosoma
hemprichi, and Tolypothrix sp. were stable at low densities, and the microcosm
ecosystem did not collapse.
As a result of the observed changes in the structural parameter, the m-NOEC
(microcosm maximum effect-free concentration) of LAS was estimated as 1 mg/L.
While the NOEC of LAS for Daphnia magna in a single-species examination was
1180–3250 μg/L and the NOEC for algae was 400–18,000 μg/L, it was thought that
the m-NOEC exhibited slight unevenness. It was shown that the evaluations of the
microcosm test using the structural parameter (i.e., population density) and the
functional parameter (i.e., the P/R ratio) were consistent. The microcosm test is an
effective tool for assessing the effects of surfactants on ecosystems because it allows
for the evaluation of the effects of surfactants from the viewpoint of the interactions
among microorganisms, material cycling, and energy flow. Based on these characteristics, the microcosm test is a useful method of performing environmental assessments that can reflect the behavior of natural aquatic ecosystems.
70
K. Murakami et al.