Environmental Engineering Reference
In-Depth Information
Table 2.3
Toxicity of fl owable carbofuran (the main liquid formulation) to mallards, expressed as
the number of square centimetres of spray deposit needed to achieve an LD
50
in the test organism
No. of cm
2
per LD
50
Duckling
b
Labeled application rate
in Canada g a.i./ha
a
Crops/pests
Adult
c
Grasshopper, wheat midge, sunfl ower beetle
in cereals, oilseeds
132
9.1
200
Alfalfa
264
4.5
100
Potatoes, corn, peppers, strawberries
528
2.3
50
Sugar beets
1123
1.1
23
Raspberries, B.C. strawberries
1200
1.0
22
Turnip, rutabaga
2520
0.48
11
a
Grams of the active ingredient (i.e., the technical pesticide) per hectare of crop
b
Assuming an LD
50
of 0.397 mg/kg (Hudson et al. 1972) for the technical material and a weight of 51 g (Martin et al.
1991).
c
Assuming an LD
50
of 0.415 mg/kg (Hudson et al. 1972) for the technical material and a weight of 1080 g (Dunning
1993).
2.3 Exposure routes for granular carbofuran formulations
2.3.1 Direct ingestion
Granular insecticides were designed for convenience. They reduce the risk to the person applying
the product, and potentially provide a 'timed', or slow/controlled release of the chemical. Since birds
do not have teeth, many species regularly consume variable quantities of grit (coarse sand, small
pebbles) which then helps them grind their food within their muscular gizzards (part of the digestive
tract). This requirement for grit is particularly high in herbivorous birds who consume vegetation
(foliage, bulbs, tubers, seeds, etc). It is thought that this is a primary reason why birds actively seek
out and consume pesticide granules (mistaking them for grit particles), although they probably also
mistake them for seed. Grit is retained within the gizzard, even when a bird is fasting and once
food has actually passed down the alimentary canal (British Ornithologists' Union 1985). The main
manufacturer of carbofuran reports that at least 45 avian species, from 17 different families, have
been killed during their supervised fi eld trials involving silica granular formulations (FMC 1986,
and see Chapter 8).
Consumption of just one to fi ve granules of Furadan 10G can be fatal to small birds (Balcomb,
Stevens and Bowen 1984a, and see Chapter 3 and Chapter 7). An average 10G granule (based on
a mean weight of 0.320 mg; Hill and Camardese 1984) contains 0.032 mg of active carbofuran,
which represents the approximate LD
50
for a small songbird. A corncob-based granule which was
also marketed in Canada as Furadan CR-10 was larger (2.25 mg; Maze, Atkins, Mineau et al. 1991)
and contained about 0.22 mg of active carbofuran. A single CR-10 granule was therefore capable of
killing even a large-bodied bird, or some of the least sensitive songbirds.
Again, it is useful to consider the application rate of the granular formulations in terms of 'rele-
vant units of poisoning potential'. For granular formulations, where granules are actively sought and
eaten by birds (very much the case with carbofuran), knowing the total number of granules applied
to an area may be useful when considering the potential for effects in wildlife, considering just one
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