Limitations of Dose-Response Terms. Several limitations must be recognized when using dose-
response data. First, it is difficult to select a test species that will closely duplicate the human
response to a specific chemical. For example, human data indicates that arsenic is a carcinogen,
while animal studies do not demonstrate these results. Second, most lethal and toxic dose data
are derived from acute (single dose, short-term) exposures rather than chronic (continuous, long-
term) exposures. A third shortcoming is that the LD
50
or LC
50
is a single value and does not
indicate the toxic effects that may occur at different dose levels. For example, in Graph 2 Chemical A is assumed to be more toxic than Chemical B based on LD
50
, but at lower doses the
situation is reversed. At LD
20
, Chemical B is more toxic than Chemical A.
TABLE 1 Summary of Dose-Response Terms Toxic Effects Category Exposure Time Route of Exposure Human Animal TD
LO
Acute or chronic All except inhalation Any nonlethal Reproductive, Tumorigenic
TC
LO
Acute or chronic Inhalation
Any nonlethal Reproductive, Tumorigenic
LD
LO
Acute or chronic All except inhalation Death
Death
LD
50
Acute
All except inhalation
Not
applicable
Death (statistically
determined)
LC
LO
Acute or chronic Inhalation
Death
Death
LC
50
Acute
Inhalation
Not
applicable
Death (statistically
determined)
(Created 12/02) UNL Environmental Health and Safety · (402) 472-4925 · http://ehs.unl.edu
