IC 50 À IC stands for inhibitory concentration; IC 50 causes a 50% decrease of
the normal response of a test organism, estimated by graphical or
computational means. IC 50 is often used to measure effects such as the
growth rate of seedlings, algae, and other organisms.
The toxicity of a compound is usually cited as the midpoint value, reported
as a mass, per unit mass (mg/kg) or volume (mg/l). This practice is misleading
and can lead to a misunderstanding or the true hazard of a compound to a
particular xenobiotic. Conversely, compounds may have different LC 50 , but the
slopes may be the same. Similar slopes may imply a similar mode of action.
Toxicity is not generated by the unit mass of xenobiotic, but by the
molecule. Therefore, molar concentration or dosage provides a more accurate
assessment of the toxicity of a particular compound. Another weakness of
LC 50 , EC 50 , and IC 50 is that they reflect the environmental concentration of the
toxicant over the specified time of the test. Compounds that move into tissues
slowly may have a lower toxicity in a 96-hour test simply because the
concentration in the target tissue has not reached toxic levels within the
specified testing time.
4
Other terminology is used to describe concentrations that have a minimal
or nonexistent effect. Those that are commonly used include:
NOEC À No observed effects concentration determined by hypothesis testing.
NOEL À No observed effects level determined by statistical hypothesis testing
methods. This parameter is reported as a dose.
NOAEC À No observed adverse effects concentration determined by
statistical hypothesis testing methods. The effect is usually chosen for its
impact on the species tested.
NOAE À No observed adverse effects level, determined by statistical
hypothesis-testing methods.
LOEC À Lowest observed effects concentration, determined by statistical
hypothesis-testing methods.
Introduction
9
[16:55 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-001.3d]
Ref: 4365 MING-HO YU Chap-001 Page: 9 1-12
FIGURE 1.4 Plot of cumulative mortality vs. environmental concentration or dose. The data are
plotted as cumulative number of deaths by each dose based on the data presented in Table 1.1.
the normal response of a test organism, estimated by graphical or
computational means. IC 50 is often used to measure effects such as the
growth rate of seedlings, algae, and other organisms.
The toxicity of a compound is usually cited as the midpoint value, reported
as a mass, per unit mass (mg/kg) or volume (mg/l). This practice is misleading
and can lead to a misunderstanding or the true hazard of a compound to a
particular xenobiotic. Conversely, compounds may have different LC 50 , but the
slopes may be the same. Similar slopes may imply a similar mode of action.
Toxicity is not generated by the unit mass of xenobiotic, but by the
molecule. Therefore, molar concentration or dosage provides a more accurate
assessment of the toxicity of a particular compound. Another weakness of
LC 50 , EC 50 , and IC 50 is that they reflect the environmental concentration of the
toxicant over the specified time of the test. Compounds that move into tissues
slowly may have a lower toxicity in a 96-hour test simply because the
concentration in the target tissue has not reached toxic levels within the
specified testing time.
4
Other terminology is used to describe concentrations that have a minimal
or nonexistent effect. Those that are commonly used include:
NOEC À No observed effects concentration determined by hypothesis testing.
NOEL À No observed effects level determined by statistical hypothesis testing
methods. This parameter is reported as a dose.
NOAEC À No observed adverse effects concentration determined by
statistical hypothesis testing methods. The effect is usually chosen for its
impact on the species tested.
NOAE À No observed adverse effects level, determined by statistical
hypothesis-testing methods.
LOEC À Lowest observed effects concentration, determined by statistical
hypothesis-testing methods.
Introduction
9
[16:55 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-001.3d]
Ref: 4365 MING-HO YU Chap-001 Page: 9 1-12
FIGURE 1.4 Plot of cumulative mortality vs. environmental concentration or dose. The data are
plotted as cumulative number of deaths by each dose based on the data presented in Table 1.1.