94
N. W. MOORE
toxic organophosphorus insecticides TEPP and malathion. The same
pesticide may have very different effects on different species. Even in
a group of closely related species the pattern of sensitivity varies from
one chemical to another. For example the partridge, the red-legged
partridge, the pheasant and the bantam have a similar response to
BHC; but the red-legged partridge is far more sensitive to heptachlor
than the bantam, while the partridge and the pheasant are intermediate, the pheasant being the less sensitive of the two (Grolleau and
Giban, 1966). In general there is least difference among mammals,
rather more among birds and fish and a very wide range of difference
among invertebrates. But even among mammals there may be considerable differences. For example DDT is four times as toxic to rats
as it is to sheep and goats. Within a species there may be a difference
in response between members of different sexes, for example in the
laboratory population of mice studied by Ozburn and Morrison (1962)
the LD50 of DDT was 500 mg/kg for males and 550 mg/kg for females.
Further there may be considerable differences between age groups.
For example Lu et al. (1965) found that the LD50 of malathion
for new born rats is 124 mg/kg but for adults is 925 mg/kg. However,
they found that adult rats were more sensitive than new born rats
to DDT and dieldrin. Individual response to a given amount of
pesticide can be considerable; variation is implicit in toxicological
testing. Even if we know the exact amount of pesticide consumed by
an animal of a species subjected to extensive toxicological study, we
are often unable to predict whether it will die or survive under natural
conditions.
The most obvious effect of a pesticide is death. It is easily perceived
in vertebrate species and its ecological effects can be assessed more
readily than others. When considering one species the mechanism by
which the pesticide causes death is often unimportant, but it may be
of significance to other species which feed upon it (see 1). 98). Animals
may take up the pesticide through their body surface, through respiratory organs or the alimentary canal. It appears that land vertebrates
mainly obtain pesticides orally, fish mainly through their gills and
arthropods both percutaneously and orally. For warm-blooded vertebrates the most used test is that for acute oral toxicity, particularly
the LD50 test which measures the amount of pesticide administered
in a single dose which is needed to kill half the members of an experimental population. The LD50 is usually expressed in terms of milligrams of pesticide to kilograms of experimental animal. In using any
toxicity test it is essential to define the time over which the dose is
given. In chronic toxicity studies the time element is introduced into
the term. By using a fixed length of dosage and observation time a
N. W. MOORE
toxic organophosphorus insecticides TEPP and malathion. The same
pesticide may have very different effects on different species. Even in
a group of closely related species the pattern of sensitivity varies from
one chemical to another. For example the partridge, the red-legged
partridge, the pheasant and the bantam have a similar response to
BHC; but the red-legged partridge is far more sensitive to heptachlor
than the bantam, while the partridge and the pheasant are intermediate, the pheasant being the less sensitive of the two (Grolleau and
Giban, 1966). In general there is least difference among mammals,
rather more among birds and fish and a very wide range of difference
among invertebrates. But even among mammals there may be considerable differences. For example DDT is four times as toxic to rats
as it is to sheep and goats. Within a species there may be a difference
in response between members of different sexes, for example in the
laboratory population of mice studied by Ozburn and Morrison (1962)
the LD50 of DDT was 500 mg/kg for males and 550 mg/kg for females.
Further there may be considerable differences between age groups.
For example Lu et al. (1965) found that the LD50 of malathion
for new born rats is 124 mg/kg but for adults is 925 mg/kg. However,
they found that adult rats were more sensitive than new born rats
to DDT and dieldrin. Individual response to a given amount of
pesticide can be considerable; variation is implicit in toxicological
testing. Even if we know the exact amount of pesticide consumed by
an animal of a species subjected to extensive toxicological study, we
are often unable to predict whether it will die or survive under natural
conditions.
The most obvious effect of a pesticide is death. It is easily perceived
in vertebrate species and its ecological effects can be assessed more
readily than others. When considering one species the mechanism by
which the pesticide causes death is often unimportant, but it may be
of significance to other species which feed upon it (see 1). 98). Animals
may take up the pesticide through their body surface, through respiratory organs or the alimentary canal. It appears that land vertebrates
mainly obtain pesticides orally, fish mainly through their gills and
arthropods both percutaneously and orally. For warm-blooded vertebrates the most used test is that for acute oral toxicity, particularly
the LD50 test which measures the amount of pesticide administered
in a single dose which is needed to kill half the members of an experimental population. The LD50 is usually expressed in terms of milligrams of pesticide to kilograms of experimental animal. In using any
toxicity test it is essential to define the time over which the dose is
given. In chronic toxicity studies the time element is introduced into
the term. By using a fixed length of dosage and observation time a