Environmental Engineering Reference
In-Depth Information
A pooled sample of gastrointestinal tracts from 20 deer mice contained 2 ppm carbofuran. The
researchers did not prepare fi eld spikes nor did they verify the recovery of carbofuran from mouse
tissue in the laboratory.
Despite several important defi ciencies in this study, some interesting observations emerge. Voles
are almost totally herbivorous while deer mice are more insectivorous. Consequently, one would
expect voles to be more susceptible to carbofuran poisoning than deer mice, though the former
may eat poisoned insects. There was a precipitous reduction in the vole population on one of the
spray sites, and calculated 'survival rates' were lower on the treated plots combined for that species.
Although overall numbers of deer mice did not change post-spray, there was a signifi cantly higher
turnover rate of young individuals on treated plots, indicating higher death or emigration from those
plots. Insuffi cient details were provided to properly assess the cholinesterase data. In any case, it is
likely that these data are biased, because severely intoxicated animals are likely to be less mobile
and have a lower trappability.
The relatively high residue level measured in the deer mice (2 ppm in gastrointestinal tracts) is
cause for concern. It was hypothesised in the study on burrowing owls (reported in 8.4.2.3) that
small mammals might provide a source of residues for the owls. Some birds of prey feed extensively
on these populations of small mammals. Given the results of the research and probable routes of
exposure, it is likely that the voles would have shown higher residue values than the deer mice.
Furthermore, small mammals may also acquire substantial residues on the surface of their fur as
they forage in treated crops, but this was not measured. In FMC research documented earlier (refer
back to Section 8.4.1.5), fi eld personnel found a paralysed northern harrier after it fed on a cot-
tontail rabbit with 0.1 ppm total body residues. The authors of the current study did not provide the
information necessary to convert the 2 ppm of residues in the pool of gastrointestinal tracts to whole
body burdens.
8.4.2.5 Martin et al. 2000
The authors of this excellently designed and executed study followed two species of nesting song-
birds (chestnut-collared longspurs (
Calcarius ornatus
) and Baird's sparrow (
Ammodramus bairdii
))
on 56 hectare plots aerially sprayed with 132 g ai of carbofuran. The bulk of the data was collected on
the longspurs. Breeding parameters, namely number of eggs, nestlings and fl edgings per nest were
not affected by spraying. Despite demonstrated brain cholinesterase depression in nestlings as high
as 70%, the data showed at most a 17% reduction in individual nestling success in nests that survived
predation. However, the number of productive Baird sparrow territories was signifi cantly reduced
in the Furadan-sprayed plots. The authors speculated that this species might be more toxicologically
susceptible to carbofuran but numbers were low and conclusions remained tentative.
8.4.3 Monitoring programmes in US cotton
Several US States attempted to monitor the application of carbofuran to cotton fi elds at the rate
of 280 g ai/ha (Fite, Randall, Young et al. 2006). The only indication of effects came from a
California monitoring programme where searchers found seven fox sparrow (
Passerella iliaca
) car-
casses as well as a ground squirrel (Family Sciuridae) in a fi eld adjacent to a carbofuran-treated
fi eld. The fi nding of so many dead birds of the same species argues for this to be pesticide-related,
but there was not enough tissue available for analysis. Other monitoring efforts did not turn up any
evidence of effects but the US EPA severely criticised these efforts as generally inadequate and
lacking in key components of adequate carcass searching practices. A more complete review can be
found in Fite, Randall, Young et al. (2006).
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