Environmental Engineering Reference
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Field personnel found 14 dead birds in the carbofuran-treated fi elds and in the edges of those fi elds
over the 14 day period comprising the two applications. By contrast, personnel found fi ve dead birds
in the edges of the control fi elds. Those fi elds had been treated with pyrethroid insecticides (which
are of low acute toxicity to birds). The authors speculated that this 'control' mortality may have been
due to exposure to pesticides used on adjacent fi elds not under experimental control. Interestingly, at
least one of the fi ve control carcasses was from a fi eld edge where the adjoining cornfi eld had been
treated with carbofuran, at 75% of the experimental rate. An immobilised but living warbler was also
associated with the same control plot. Furthermore, edge vegetation from all fi elds where carcasses
were found contained detectable carbofuran residues. Therefore, all carcasses found post-treatment
in this study were associated with some carbofuran use, either experimentally or incidentally.
The investigators analysed the gastrointestinal tracts and/or brains of 11 birds found dead on
carbofuran-treated plots for presence of the compound. All but two birds had detectable residues.
However, since fi eld personnel collected these two birds at fi ve and six days post-spray, chemical
degradation likely accounts for the lack of detectable residues in these carcasses (further expanded
on in Chapter 2).
Poor analytical recovery made detecting carbofuran residues in any carcass even more improb-
able. The authors looked at the persistence of residues injected into the gastrointestinal tracts of
carcasses left to age in the fi elds and others spiked in the laboratory. Recovery of carbofuran from
the gastrointestinal tracts of four birds analysed immediately (0.5 hour) after laboratory spiking
ranged from 0.5 to 1.3 ppm (7.3 to 19% of that expected). Birds spiked in the fi eld and then taken
to the laboratory rarely had levels that were quantifi able (above 0.10 ppm) and levels were usually
below the detection limit (less than 0.05 ppm). One may therefore conclude that fi nding carbofuran
residues in fi eld-recovered carcasses is a signifi cant event (again, refer to Chapter 2). This is in sharp
contrast to the long persistence of carbofuran in acid soils (on the order of months) as documented
in Section 8.2.2.2.
The researchers made several observations of 'defi cit behaviour', that is to say any behaviour
judged to be abnormal. However, it seems that some fi eld personnel had diffi culty judging whether
individuals were behaving abnormally, and certain reports lacked good descriptions of the abnormal
behaviours observed. Only one type of abnormal behaviour, immobilisation of the bird, is unequivo-
cal. This effect is typical of cholinesterase-inhibiting insecticides and less likely to be misinterpreted
by a fi eld observer. The researchers found four birds immobilsed on the Nebraska fi elds. Of these,
one was the aforementioned warbler associated with a 'control' edge next to carbofuran use, and the
other three were on carbofuran-treated plots.
Field personnel found carcasses of other animals, mostly mammals and amphibians. These car-
casses were associated with both treated and control fi elds but were found primarily in fi eld edges,
making an interpretation diffi cult for reasons mentioned above. Four of seven non-bird carcasses
found post-treatment and analysed had measurable quantities of carbofuran in their gastrointesti-
nal tracts. Study authors suggested an association between carbofuran treatment and amphibian
mortality after fi nding four southern leopard frogs (
Rana sphenocephala
) at the edge of a carbofuran-
treated plot between two and six hours after application.
In all, fi eld personnel searched an area of approximately 32 hectares, divided equally between
fi eld and edge, for carcasses in the carbofuran-treated fi elds. This represents an uncorrected kill rate
of 0.43 birds per hectare.
8.4.1.4 FMC 1989a Texas/New Mexico pivot-irrigated fi eld
Despite the different outward appearance of these fi elds (i.e., perfect circles, 800 metres in diam-
eter) and the nature of the fi eld edge habitat (which was concentrated in the non-cropped corners
of the square fi elds), the methods used in this study were very similar to the methods used in the
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