industrial and construction sites, and railways and railway embankments, as they kill
all plant material with which they come into contact. Apart from selective/
nonselective herbicides, other important distinctions among these chemicals include
their persistence (i.e., their residual action or how long the product stays in place and
remains active), means of uptake (whether it is absorbed by aboveground foliage
only, through roots, or by other means), and the mechanism of action. Historically,
products such as common salt and other metal salts were used as herbicides;
however, these have gradually fallen out of favor, and in some countries, a number
of these are banned due to their persistence in soils and toxicity and due to concerns
regarding groundwater contamination. Herbicides have also been used in warfare
and armed conflicts. Modern herbicides are often synthetic mimics of natural plant
hormones, which interfere with the growth of target plants. The term “organic
herbicide” has come to mean herbicides intended for organic farming. Some plants
also produce their own natural herbicides, such as the genus Juglans (walnuts) or the
tree of heaven; the actions of natural herbicides and other related chemical interactions are termed allelopathy. Due to herbicide resistance, a major concern in agriculture, a number of products combine herbicides with different means of action.
Integrated pest management may use herbicides alongside other pest control
methods.
Though herbicides are known to exhibit high toxicity in the aquatic ecosystems
that contain biological interactions, material circulation, and energy flow, the environmental risk associated with the use of herbicides remains poorly understood. The
microcosm, which is a model microbial ecosystem consisting of a producer, consumers, and decomposers, is useful for evaluating the environmental risk to an
ecosystem, and positioning of this model ecosystem as the standard docimasy is
thus important.
7.3.1 Linuron
The addition concentration of Linuron was adjusted to 0.01, 0.05, 0.1, 1.0, and
3.0 mg/L, and it was added on the 16th day of the stable state into the microcosm.
The endpoints were abundance (structural parameter) and the DO concentration
(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, and 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 onward, and the P/R
ratio was calculated from the amounts of production (P) and respiration (R).
The m-NOEC of Linuron as a herbicide was determined to be 0.1 mg/L using the
functional parameter (Fig. 7.8), but no effect was observed in the time series of biotic
succession. It was also determined that the m-NOEC of Linuron as herbicide was in
the range of 1–10 mg/L by the structural parameter. The activity of the microcosm
increased with the addition of 1 mg/L and decreased with the addition of 10 mg/L of
Linuron. The strength of Linuron loading (i.e., the influence concentration) was
7 Example Assessments of the Microcosm N-System
83
all plant material with which they come into contact. Apart from selective/
nonselective herbicides, other important distinctions among these chemicals include
their persistence (i.e., their residual action or how long the product stays in place and
remains active), means of uptake (whether it is absorbed by aboveground foliage
only, through roots, or by other means), and the mechanism of action. Historically,
products such as common salt and other metal salts were used as herbicides;
however, these have gradually fallen out of favor, and in some countries, a number
of these are banned due to their persistence in soils and toxicity and due to concerns
regarding groundwater contamination. Herbicides have also been used in warfare
and armed conflicts. Modern herbicides are often synthetic mimics of natural plant
hormones, which interfere with the growth of target plants. The term “organic
herbicide” has come to mean herbicides intended for organic farming. Some plants
also produce their own natural herbicides, such as the genus Juglans (walnuts) or the
tree of heaven; the actions of natural herbicides and other related chemical interactions are termed allelopathy. Due to herbicide resistance, a major concern in agriculture, a number of products combine herbicides with different means of action.
Integrated pest management may use herbicides alongside other pest control
methods.
Though herbicides are known to exhibit high toxicity in the aquatic ecosystems
that contain biological interactions, material circulation, and energy flow, the environmental risk associated with the use of herbicides remains poorly understood. The
microcosm, which is a model microbial ecosystem consisting of a producer, consumers, and decomposers, is useful for evaluating the environmental risk to an
ecosystem, and positioning of this model ecosystem as the standard docimasy is
thus important.
7.3.1 Linuron
The addition concentration of Linuron was adjusted to 0.01, 0.05, 0.1, 1.0, and
3.0 mg/L, and it was added on the 16th day of the stable state into the microcosm.
The endpoints were abundance (structural parameter) and the DO concentration
(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, and 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 onward, and the P/R
ratio was calculated from the amounts of production (P) and respiration (R).
The m-NOEC of Linuron as a herbicide was determined to be 0.1 mg/L using the
functional parameter (Fig. 7.8), but no effect was observed in the time series of biotic
succession. It was also determined that the m-NOEC of Linuron as herbicide was in
the range of 1–10 mg/L by the structural parameter. The activity of the microcosm
increased with the addition of 1 mg/L and decreased with the addition of 10 mg/L of
Linuron. The strength of Linuron loading (i.e., the influence concentration) was
7 Example Assessments of the Microcosm N-System
83