Environmental Engineering Reference
In-Depth Information
Dietricht and colleagues (1995) also reported on a large mortality of buzzards, as well as black and
red kites (
Milvus milvus
and
Milvus migrans
, respectively). These birds were killed via the inges-
tion of earthworms in a beet fi eld that had been treated with granular carbofuran applied in-furrow.
Earthworm residues peaked at 3.2 ppm in one seeded fi eld studied by Dietricht, Schmid, Zweifel
et al. (1995). Stinson, Hayes, Bush et al. (1994) further report the poisoning of American kestrels
following an application of the 15G formulation in-furrow. Stomach contents of two birds affected
contained only insect parts.
The acute LD
50
of technical grade carbofuran in the mouse is approximately 2.0 mg/kg bw
(NRCC 1979). It is therefore likely that small mammals such as moles and shrews, which regularly
consume earthworms, are very much at risk from the use of granular carbofuran. Observed behav-
ioural changes in exposed worms, such as muscle spasms and coiling, are likely to attract predators
(reviewed in NRCC 1979). There is no readily available information regarding carbofuran in (or on)
other soil invertebrates. Any such contamination of invertebrate fauna would certainly add to the
already high risk of exposure.
2.3.3 Contaminated soil/sediments
Carbofuran granules have caused many instances of waterfowl mortality, in fl ooded or partly fl ooded
fi elds (see Chapter 8). When fi elds fl ood (or puddles form), even if this occurs a long time after
application, waterfowl (primarily) are often attracted to those fi elds. They then sift waterlogged
sediments in search of food, and drink the contaminated water. The label for Furadan 10G speci-
fi es that the granules should not be applied to soil subject to fl ooding. Problems have primarily
arisen in acidic soils, where granules have a much longer half-life (Getzin 1973). Root crops are
often grown on soils where there is high water retention. Clearly, it is often diffi cult for growers to
foresee puddle formation or fl ooding which may take place some time after the application of the
pesticide. Wilson and colleagues (2002) found that granulated carbofuran followed a logistic decay
model in both silt loam and muck soils (in the lower Fraser Valley of British Columbia). Very high
initial retention of the active ingredient occurred, and half-lives of 129 and 97 days for the two soil
types were noted, respectively. Further discussion of half-life and fate in tropical soils can be found
in Chapter 3.
2.4 The time course of carbofuran intoxication
Early studies which related cholinesterase levels to acute exposure to carbamates are those of
Bunyan and Jennings (1976) and Westlake, Bunyan, Martin et al. (1981), although these authors did
not test carbofuran specifi cally. One fi nding which emerged was that for a number of carbamates,
birds that died within two hours of exposure did not necessarily demonstrate any inhibition of brain
acetylcholinesterase (AChE). Brain AChE inhibition only became obvious at higher (e.g., 2 x LD
50
)
doses. Westlake and colleagues suggested that this may be because carbamates have a higher affi nity
for neuromuscular junctions (relative to organophosphates). Death from carbamate intoxication is
typically very rapid, e.g., it occurs after just 9 to 18 minutes, for three granular carbamate insecti-
cides (Balcomb, Stevens and Bowen 1984a). Hence, an animal presumably dies of respiratory arrest
long before signifi cant quantities of the insecticide pass into the brain. On the other hand, plasma
cholinesterase (ChE) was much more indicative of exposure at > 2h post dosing, whether the animal
died or survived. At 24h post dosing, the plasma activity of survivors returned to normal, and in
some cases was higher than in controls.
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