Impacts of carbofuran on birds in Canada and the United State - Carbofuran and Wildlife Poisoning: Global Perspectives and Forensic Approaches - page 228

Nebraska study, described previously in Section 8.4.1.3. Results were also similar and confi rmed
those obtained previously.
Again, the investigators reported serious problems of chemical accountability. The recoveries
of three spray tank samples ranged from 22 to 41% of the expected amount of carbofuran active
ingredient. Collection cards positioned high in the corn canopy showed mean fi eld deposits rang-
ing from 19 to 70% of nominal rate, with an average of 36%. These applications are somewhat
better than those on the Nebraska plots (with a grand mean of 22%) but still poor from the point
of view of effi cacy and pest management. The report also noted considerable contamination of
fi eld edges.
Researchers found 17 dead birds in the carbofuran fi elds and edges post-treatment, with a roughly
equal proportion in both habitats. Field personnel recorded most of this mortality within two days
of a carbofuran application. This compares with two dead birds found in the control plots (one in a
fi eld, the other in a fi eld edge). The farmer had treated the control fi elds in this study with dimethoate
applied in cottonseed oil and with a 'control application' of a pyrethroid. We reiterate that it is mean-
ingless to look at pre-treatment mortality given the range of pre-treatment sprays made in control
and treated fi elds (again, ethyl parathion was used on some plots). All bird carcasses analysed for
carbofuran had quantifi able residues in their gastrointestinal tracts (ranging from 0.2 to 2.4 ppm).
The researchers reported fi nding three immobilised birds, including one bird of prey (northern
harrier) on the Texas/New Mexico plots. Two birds were found on control fi elds. However, there
were detectable carbofuran residues in these 'control' edges. Residues in the edges of the control
fi eld with the immobilised harrier were identical to those in the edges of treated fi elds four days
post-application (13.3 ppm).
Non-bird mortality was also interesting. Researchers found eight dead amphibians (toads,
frogs, and salamander) and one mouse (Genus Peromyscus ) on carbofuran plots post-treatment. All
had quantifi able carbofuran residues in their gastrointestinal tracts, ranging from 0.1 to 9.4 ppm.
Researchers also found a dead mouse (unspeciated) and a skink (a type of lizard) in the edges of
control fi elds.
The fi nding of dead amphibians with high gut residue levels in these Texas study plots com-
bined with the observation of the four dead leopard frogs associated with a carbofuran spray in the
Nebraska study indicates that amphibians are at risk from carbofuran use. The researchers did not
provide residue analyses for these specimens, and provided no reason for excluding these data from
the report.
Given a similar search area in the Texas/New Mexico plots, about 32 hectare divided equally
between fi eld and edge, yields an uncorrected mortality rate of 0.53 birds per hectare.
Based on carcass search effi ciency (where the ability of search crews to fi nd dead birds is assessed
with planted birds or decoys) and scavenger rate measures (where carcasses are placed in fi elds
and the time it takes for them to be scavenged/removed by scavengers is measured), Mineau (2005)
suggested that the true kill rates for the sprayed cornfi elds in the Nebraska and Texas studies were
2.4 and 2.0 carcasses per hectare respectively.
8.4.1.5 FMC 1989b: alfalfa studies, Kansas
Using the same basic design in alfalfa fi elds as in the corn studies previously reported (see Sections
8.4.1.2 and 8.4.1.3), researchers conducted studies in Kansas and Oklahoma. Collaborating farmers/
applicators treated 16 fi elds (eight in each study area) twice with Furadan 4F by ground (Kansas)
or by air (Oklahoma). They fi rst applied 1.1 kg ai/ha and then half that rate about one or two
months later. The design of these studies was compromised because the farmers also treated the
carbofuran-treated and control fi elds with carbaryl or methomyl as needed and treated control fi elds with
chlorpyrifos. Thus, of the planned eight pairs of treated-control fi elds in Oklahoma, only two pairs