Environmental Engineering Reference
In-Depth Information
kill rate of 0.22 birds per hectare. Of the seven carcasses, searchers found four after the second
(lighter) spray. Searchers also recovered 17 bird carcasses from the control plots treated with chlor-
pyrifos (compared with three in the combined pre-treatment periods). Searchers found two immo-
bilised birds, both on chlorpyrifos-treated plots. Other carcasses, including mammals, reptiles, and
amphibians, were also retrieved from both carbofuran- and chlorpyrifos-treated plots post-spray.
Of nine carcasses found post-spray on the chlorpyrifos search plots and subsequently analysed,
eight contained chlorpyrifos residues in either the gastrointestinal tract or the brain. Similarly, carbo-
furan residues were detected in three of four carcasses analysed from the carbofuran-treated plots
post-treatment.
Industry studies have clearly shown that carbofuran applied by ground or by air, at either 0.55 or
1.1 kg ai/ha onto alfalfa and adjacent fi eld margins, kills birds and other vertebrates. The estimated
bird kill rates corrected for searching and scavenging, were 1.1 and 0.61 birds per hectare for Kansas
and Oklahoma fi elds respectively. Chlorpyrifos, an alternative to carbofuran, applied at 1.1 and
0.55 kg ai/ha, also caused bird mortality. However, the studies were inadequate for evaluating the
effects of chlorpyrifos use. That is, researchers did not monitor the chlorpyrifos applications, and
there is the confounding aspect that all the control fi elds had measurable carbofuran residues at their
fi eld edges, presumably due to spraying in neighbouring fi elds. The researchers did not analyse
carcasses found on chlorpyrifos-treated plots for residues of carbofuran.
8.4.2 Field studies of carbofuran used as a grasshopper insecticide
Grasshopper control was a main registered use pattern of carbofuran in Canada until it was can-
celled by the regulatory authorities following unacceptable impacts and risk to the burrowing owl,
an endangered species. These studies stand out from the industry studies previously reported because
of the extremely low application rate of carbofuran (132 g ai/ha). We believe this is the lowest
rate of the product registered anywhere in the world.
8.4.2.1 Horstman 1985, Horstman and Code 1987
These studies examined the effect on nesting Brewer's blackbirds (
Euphagus cyanocephalus
) and
other passerine species of carbofuran sprayed on roadside verges at the low rate of 132 g ai/ha to con-
trol grasshoppers. About 60% of the spraying was applied aerially and the remaining using ground
equipment. Egg and nestling mortality rates were signifi cantly higher in sprayed nests, principally as
a result of single egg or nestling disappearances. Such a disappearance at the earlier stages of nest-
ing suggests abandonment of the nest and/or loss (i.e., mortality) of the adults. Of eight treated nests
with such disappearances, fi ve had been sprayed with carbofuran, the others with other insecticides.
Total nest abandonment was also higher in treated nests, but sample size was too small for statistical
analysis. Field personnel found some dead nestlings, but these did not contain detectable residues.
Horstman (1985) concluded that nestlings might be at risk from eating carbofuran-treated insects.
However, she also postulated that habitat differences may have led to uneven predation rates, with
untreated nests being in habitats less prone to predation.
Horstman and Code (1987) designed a study to verify Horstman's 1985 work and to add to the
sample size. This was a planned study in which the investigators applied carbofuran themselves by
ground rig for a distance of 0.4 kilometres along the roadside on either side of the nests. Some nests
were exposed to two sprays ten days apart. The researchers only monitored Brewer's blackbirds.
Unlike observations made in the previous study, the researchers noted that adult females foraged
principally in the fi elds adjoining the road verges rather than in the verges themselves. However,
Hostman and Code did not quantify the relative importance of these habitats. This time, they found
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