toxicity. In order to quantify and characterize the toxicity of a pesticide, critical
concentrations (C crit ) such as the median lethal concentration (LC 50 ), the median
effect concentration (EC 50 ) or the no-effect concentration (NOEC) are experimentally determined and used in an eco-toxicological risk assessment (Palma et al.
2004). The LC 50 of a pollutant is the concentration at which 50 % of individuals of a
test population are killed due to exposure to the pollutant. The EC 50 has the same
statistical meaning as the LC 50 , but is related to sub-lethal effects. In the case of
fish, the number of eggs per female affected by the concentration of a contaminant
is a good way to establish the presence or not of such sub-lethal effects. The NOEC
is the concentration of a pollutant that does not harm a test species with regard to the
effect under study.
Table 4.3 shows the LC 50 , EC 50 and NOEC for seven pesticides used in the Mae
Sa watershed area in Thailand. In toxicological studies, toxicity is typically determined for species of the three main trophic levels: algae (producers), zooplankton
(consumers I) and fish (consumers II). A herbicide such as atrazine, that is, a
compound that was designed for weed control, has a low EC 50 with regard to
algae but a very high EC 50 with regard to zooplankton. For insecticides such as
cypermethrin; however, the opposite is true; it has a high EC 50 for algae but a very
low EC 50 for zooplankton.
In order to assess the potential risk to aquatic ecosystems of using pesticides, a
frequently used approach is the so-called risk quotient (RQ) (Commission of
European Communities 2003; Palma et al. 2004; Vryzas et al. 2009). The RQ is
computed as a function of environmental exposure and eco-toxicological effects,
and is the ratio between the predicted environmental concentration (PEC) and the
predicted no-effect concentration (PNEC).
RQ ¼
PEC
PNEC
(4.1)
Table 4.3 Toxicity (in water) of the seven selected pesticides under study
Pesticide
Algae
Zooplankton
Fish
EC 50
(mg L
À1
)
NOEC
(mg L
À1
)
EC 50
(mg L
À1
)
NOEC
(mg L
À1
)
LC 50
(mg L
À1
)
NOEC
(mg L
À1
)
Dichlorvos
52,800
4,730
0.19
–
550
110
Atrazine
59
100
85,000
250
4,500
2,000
Dimethoate
90,400
3,200
2,000
40
30,200
400
Chlorothalonil 210
33
84
9
38
3
Chlorpyrifos 480
43
0.1
4,6
1.3
0.14
Endosulfan
2,150
–
440
–
2
0.0001
Cypermethrin >100
1,300
0.3
0.04
2.8
0.03
Notes: Toxicity data for the three trophic organisms obtained from PPDB 2009. A bold number
indicates that this concentration was used as a critical concentration for the calculation of the risk
quotient (see Table 4.4)
LC 50 median lethal concentration, EC 50 median effect concentration, NOEC no observed effect
concentration
160
M. Lamers et al.
concentrations (C crit ) such as the median lethal concentration (LC 50 ), the median
effect concentration (EC 50 ) or the no-effect concentration (NOEC) are experimentally determined and used in an eco-toxicological risk assessment (Palma et al.
2004). The LC 50 of a pollutant is the concentration at which 50 % of individuals of a
test population are killed due to exposure to the pollutant. The EC 50 has the same
statistical meaning as the LC 50 , but is related to sub-lethal effects. In the case of
fish, the number of eggs per female affected by the concentration of a contaminant
is a good way to establish the presence or not of such sub-lethal effects. The NOEC
is the concentration of a pollutant that does not harm a test species with regard to the
effect under study.
Table 4.3 shows the LC 50 , EC 50 and NOEC for seven pesticides used in the Mae
Sa watershed area in Thailand. In toxicological studies, toxicity is typically determined for species of the three main trophic levels: algae (producers), zooplankton
(consumers I) and fish (consumers II). A herbicide such as atrazine, that is, a
compound that was designed for weed control, has a low EC 50 with regard to
algae but a very high EC 50 with regard to zooplankton. For insecticides such as
cypermethrin; however, the opposite is true; it has a high EC 50 for algae but a very
low EC 50 for zooplankton.
In order to assess the potential risk to aquatic ecosystems of using pesticides, a
frequently used approach is the so-called risk quotient (RQ) (Commission of
European Communities 2003; Palma et al. 2004; Vryzas et al. 2009). The RQ is
computed as a function of environmental exposure and eco-toxicological effects,
and is the ratio between the predicted environmental concentration (PEC) and the
predicted no-effect concentration (PNEC).
RQ ¼
PEC
PNEC
(4.1)
Table 4.3 Toxicity (in water) of the seven selected pesticides under study
Pesticide
Algae
Zooplankton
Fish
EC 50
(mg L
À1
)
NOEC
(mg L
À1
)
EC 50
(mg L
À1
)
NOEC
(mg L
À1
)
LC 50
(mg L
À1
)
NOEC
(mg L
À1
)
Dichlorvos
52,800
4,730
0.19
–
550
110
Atrazine
59
100
85,000
250
4,500
2,000
Dimethoate
90,400
3,200
2,000
40
30,200
400
Chlorothalonil 210
33
84
9
38
3
Chlorpyrifos 480
43
0.1
4,6
1.3
0.14
Endosulfan
2,150
–
440
–
2
0.0001
Cypermethrin >100
1,300
0.3
0.04
2.8
0.03
Notes: Toxicity data for the three trophic organisms obtained from PPDB 2009. A bold number
indicates that this concentration was used as a critical concentration for the calculation of the risk
quotient (see Table 4.4)
LC 50 median lethal concentration, EC 50 median effect concentration, NOEC no observed effect
concentration
160
M. Lamers et al.