Environmental Engineering Reference
In-Depth Information
median lethal doses in half, we can estimate how many individuals, on average, could be killed from a
single tablet-sized amount of the pesticide. We have used this concept in the tables that follow.
Carbofuran is classifi ed by the World Health Organisation (WHO) as extremely hazardous to
humans (WHO 1A) based on acute oral rat LD
50
values as low as 8 mg/kg (Health and Welfare
Canada 1987). This same value (a few drops only) is potentially lethal to a mammal of average sen-
sitivity (Table 2.1). In comparison, this value of 8 mg/kg represents the approximate LD
50
known for
the
least
sensitive bird species tested to date (the European starling,
Sturnus vulgaris
). The average
toxicity of several carbamate insecticides to the rat, the 'average' mammal and the average bird is
given in Table 2.1. Note that it is not unusual for birds to be far more susceptible than mammals to
cholinesterase-inhibiting insecticides. This is the case for carbofuran, methiocarb and propoxur -
although the trend is reversed for carbaryl (and to a lesser extent aldicarb). Note also that the LD
50
values given for carbofuran in Table 2.2 are below 1 mg/kg for the two species of waterfowl tested,
for half of the songbirds, and for one of the two birds of prey. A single aspirin-sized tablet of techni-
cal grade carbofuran contains enough toxicant to kill more than 20 000 red-billed quelea (
Quelea
quelea
). In comparison with other pesticides, carbofuran has one of the highest recorded toxicities to
birds of any insecticide registered worldwide.
All of these data are for the unformulated technical grade material. The gavage liquid that is used
in experiments (unless the material is given neat in a gelatine capsule) can vary from test to test, and
this is an important source of variance in the test results. The fl owable formulation (Furadan 480F
or Furadan 4F in the United States - see Chapter 8) may also be approximately 1.7 times as toxic as
the technical grade active ingredient to the same species (E.F. Hill, U.S. Fish and Wildlife Service
Bulletin). However, Hill and Camardese (1984) found no signifi cant difference in toxicity between
technical grade carbofuran and the 10% sand core granule formulation (Furadan 10G) toward north-
ern bobwhite (a species of quail commonly used for pesticide testing in North America).
Using species sensitivity distributions, Mineau and colleagues (2001) calculated that
the LD
50
value at the 5% species sensitivity tail (a common benchmark amongst pesticide
Table 2.1
Rat LD
50
values and median mammal and bird values for all species tested. Data from a
database compiled by Environment Canada
Average
(geometric)
rat LD
50
Aspirin®
index
a
for the
average rat
Median mammal
LD
50
(no. of
species tested)
Median avian
LD
50
(no. of
species tested)
Compound
WHO listing
Carbofuran
1B
Highly hazardous
8.7
64
8.9 (6)
1.65 (18)
Aldicarb
1A
Extremely hazardous
0.79
709
1.15 (6)
2.82 (10)
Carbaryl
II
Moderately hazardous
449
1.2
424 (8)
1870 (7)
Methiocarb
1B
68.7
8.1
40.9 (5)
7.5 (33)
Methomyl
1B
25.4
22
24.5 (7)
23.7 (13)
Propoxur
II
80.3
7.0
146 (6)
11.8 (23)
Number of rats that would be killed by a tablet-sized quantity of carbofuran. Necessary inputs into the calculation:
each tablet weighs approximately 392 mg, and a rat weighs 350g (the geometric average of typical male and female
weights). Thus, an LD
50
of 8.7 mg/kg bw means that 8.7 mg would be needed to kill a 1 kg rat (if such existed).
Therefore, an estimated 3.05 mg (8.7
0.35) is needed to kill a 350 g (average) rat. Since a tablet weighs 392 mg, it
contains 128 'potentially' lethal doses (392
3.05). And, since only half those doses will actually be lethal (LD
50
),
1 tablet-sized quantity of carbofuran is suffi cient to kill 64 rats.
a
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