outbreaks of algae—if discharged carelessly. In this section, the WET test was used
to investigate the influence of rice-washed effluent on the microcosm (i.e., the model
of the natural ecosystem). Additionally, the influence of rice-washed effluent on the
ecosystem in which it was discharged was determined based on the toxicity units
(TUs) of the m-NOEC.
Rice-washed wastewater that was suction filtered using a 0.45 μm diameter
membrane (ADVANTEC, GS-45) was added at a stable stage 16 days after microcosm cultivation began, and the addition concentrations were set to 0%, 5%, 10%,
20%, 40%, and 80% of the microcosm medium. The impact of rice-washed effluent
was estimated from both the P/R ratio (Sugiura 2010) as the functional parameter
and the abundance of microbiota (Murakami et al. 2016) as the structural parameter
in the microcosm. The environmental impact and ecological risk were estimated by
comparing the microcosm with the no-addition system (i.e., the control system)
using both assessment methods.
As the addition concentration increased in comparison with the control system,
the amplitude of the DO increased, and the rice-washed effluent raised the bioactivity in the microcosm. The time series of the P/R ratio was stable, and both phytoplankton (producers) and zooplankton (consumers) were assumed to multiply
together with all addition concentrations (i.e., 0%, 5%, 10%, 20%, 40%, and 80%)
in the microcosm. Because Æ34.13% of the control system values of the slope a in
the regression equation were 0.0025 ≦ a ≦ 0.0051, it was determined that there was
no influence in the 10% addition system. Because Æ34.13% of the control system
values of the coefficient of variation cv exhibited amplitudes wherein 0.099 ≦ cv ≦
0.20, it was determined that all addition concentrations of rice-washed effluent had
an impact on the ecosystem. Based on the functional parameter (P/R ratio), all
addition concentrations also had an influence on the ecosystem. However, there
was no influence noted for any addition concentrations based upon the structural
parameter because no population declines or extinctions were observed.
A microcosm-WET test for rice-washed effluent was conducted, and the influence of the rice-washed effluent on the m-NOEC was less than 5% in both the
functional and the structural parameters. Furthermore, the toxicity unit (TU) was
determined to be 20, so dilution by more than 20 times was necessary. It is also
necessary to examine the consistency using statistical analyses, and a branching-type
analysis of variance was used to validate these findings; this simple statistical
technique is described in the microcosm test method manual.
9.3.4 Paddy Field Effluent
Paddy field effluent, after pesticide spraying, was suction filtered using a 0.45 μm
diameter membrane (ADVANTEC, GS-45) and added at a stable stage on the 16th
day after microcosm cultivation began. The addition concentrations were set to 0%,
25%, 50%, and 100% of the microcosm medium. The abundance of Cyclidium
glaucoma decreased in the 50% addition system, as shown in Figs. 9.6 and 9.7, and
became extinct in the 100% addition system. Therefore, it was determined that a
9 Application to the Whole Effluent Toxicity Test
175
to investigate the influence of rice-washed effluent on the microcosm (i.e., the model
of the natural ecosystem). Additionally, the influence of rice-washed effluent on the
ecosystem in which it was discharged was determined based on the toxicity units
(TUs) of the m-NOEC.
Rice-washed wastewater that was suction filtered using a 0.45 μm diameter
membrane (ADVANTEC, GS-45) was added at a stable stage 16 days after microcosm cultivation began, and the addition concentrations were set to 0%, 5%, 10%,
20%, 40%, and 80% of the microcosm medium. The impact of rice-washed effluent
was estimated from both the P/R ratio (Sugiura 2010) as the functional parameter
and the abundance of microbiota (Murakami et al. 2016) as the structural parameter
in the microcosm. The environmental impact and ecological risk were estimated by
comparing the microcosm with the no-addition system (i.e., the control system)
using both assessment methods.
As the addition concentration increased in comparison with the control system,
the amplitude of the DO increased, and the rice-washed effluent raised the bioactivity in the microcosm. The time series of the P/R ratio was stable, and both phytoplankton (producers) and zooplankton (consumers) were assumed to multiply
together with all addition concentrations (i.e., 0%, 5%, 10%, 20%, 40%, and 80%)
in the microcosm. Because Æ34.13% of the control system values of the slope a in
the regression equation were 0.0025 ≦ a ≦ 0.0051, it was determined that there was
no influence in the 10% addition system. Because Æ34.13% of the control system
values of the coefficient of variation cv exhibited amplitudes wherein 0.099 ≦ cv ≦
0.20, it was determined that all addition concentrations of rice-washed effluent had
an impact on the ecosystem. Based on the functional parameter (P/R ratio), all
addition concentrations also had an influence on the ecosystem. However, there
was no influence noted for any addition concentrations based upon the structural
parameter because no population declines or extinctions were observed.
A microcosm-WET test for rice-washed effluent was conducted, and the influence of the rice-washed effluent on the m-NOEC was less than 5% in both the
functional and the structural parameters. Furthermore, the toxicity unit (TU) was
determined to be 20, so dilution by more than 20 times was necessary. It is also
necessary to examine the consistency using statistical analyses, and a branching-type
analysis of variance was used to validate these findings; this simple statistical
technique is described in the microcosm test method manual.
9.3.4 Paddy Field Effluent
Paddy field effluent, after pesticide spraying, was suction filtered using a 0.45 μm
diameter membrane (ADVANTEC, GS-45) and added at a stable stage on the 16th
day after microcosm cultivation began. The addition concentrations were set to 0%,
25%, 50%, and 100% of the microcosm medium. The abundance of Cyclidium
glaucoma decreased in the 50% addition system, as shown in Figs. 9.6 and 9.7, and
became extinct in the 100% addition system. Therefore, it was determined that a
9 Application to the Whole Effluent Toxicity Test
175