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in plant samples collected from both Isiolo and Laikipia Districts. A higher concentration of carbo-
furan was observed in the fi rst sampling (October) than in the second (June) because most crops
were still green (i.e., the photosynthetic process was at its apex) in October, resulting in a higher
insecticidal concentration in the leaves. The difference in mean concentrations of carbofuran and its
metabolites in plants collected during the dry and wet seasons in both regions was also signifi cant
(p < 0.05), with higher concentrations observed during the wet seasons.
3.6.2.3 Soil residue results
Carbofuran residues were detected in soil and, as was the case with the plant samples, the concentra-
tion was higher during the wet season. This is because the compound readily dissolves and percolates
towards the soil matrix shortly after application. In-furrow application is meant to reduce cases of
exposure and poisoning, however, this practice has repeatedly given rise to extensive bird mortality
in organisms that sift through soil (see Chapters 7 and 8). However, we did not encounter any such
cases of fi eld poisoning during sampling and no additional investigation was done. Mean concentra-
tions of carbofuran, 3-ketocarbofuran and 3-hydroxycarbofuran varied both regionally and seasonally
(p < 0.05) in soil sampled.
Carbofuran metabolites were also found at low concentrations in the soil samples taken from
the site at Lewa Wildlife Conservancy where two lions were poisoned and over 20 vultures were
found dead. Similar soil contamination, from laced carcasses, has been reported by Vyas, Spann,
Albers et al. (2003). Pesticide residues can be transferred to the surface of the soil from a laced
carcass, either during lacing or from seepage. Since the survey established that no other forms
of carbofuran (i.e., liquid formulations) were available in the two districts, the carcass was most
likely baited with granular carbofuran. Concentrations of the compound and its metabolites in
soil from other sampling sites were signifi cantly elevated and indicated usage of carbofuran in the
two districts.
3.6.2.4 Analysis of vulture samples
In addition to some of the more mundane sampling diffi culties (described by Crocker 2005), the
author found it challenging to locate fresh carcasses of birds that had died from poisoning due to fac-
tors that included the vast extent of the land around the conservancies, the overall hostility and sus-
picion of the pastoral community and having to remain vigilant against attack by bandits and cattle
rustlers. Given the inherent diffi culty in fi nding fresh avian tissues, feet (i.e., talons) and beaks were
collected for analysis instead, following the method of Vyas, James, Craig et al. (2005). Although
the length of time that the samples (see Figures 3.16 and 3.17) were in the fi eld after exposure could
not be ascertained, residues of carbofuran were nonetheless detected in the beaks and feet, providing
positive confi rmation that the vultures were exposed to this pesticide before they died.
Vultures that ingest carbofuran-poisoned tissues very rapidly become (acutely) intoxicated/coma-
tose and are frequently recovered dead, right beside a poisoned carcass (Brown 1997). While the
residue levels detected in the feet and beaks do not necessarily imply exposure to a lethal dermal or
oral dosage, they do provide evidence that the bird in question was exposed to carbofuran (Stroud
and Adrian 1996). According to Martin and Forsyth (1998), despite the tougher, scalier skin of bird
feet/talons, they are by no means impermeable to pesticides, which implies that the birds may have
absorbed a higher amount of the compound than indicated by the residue levels detected in the feet,
which should be viewed as a lower level of exposure. Vultures and other scavenging birds step on
a carcass as they feed, providing plenty of opportunities for a pesticide/contaminant to be absorbed
dermally or through the foot pads. This explains the presence of carbofuran and its metabolites on
the birds' feet, even if in low concentrations.
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