Environmental Engineering Reference
In-Depth Information
following one poisoning event (May 2007 in Lewa) presents a signifi cant negative impact on the
demographic viability of this species.
3.6.1 Survey result
Furadan appears to have been primarily used in the two districts as a pesticide to control soil dwell-
ing and foliar feeding pests in maize cultivation and on horticultural farms. The survey showed that
over 70% of the large-scale farmers who use Furadan are situated in Laikipia District. The survey
also confi rmed that all incidents of wildlife poisoning by farmers and pastoralists in the two districts
were carried out to avenge the killings of their livestock by lions. This practice, and lion mortality in
Kenya, was discussed in Section 3.4.
Although alternative compounds such as methomyl (90% w/w), Mocap GR10, Nemur 400EG
and bio-pesticides like nimbecidine and bio-nematon were available on the market, farmers seem to
favour carbofuran (i.e., Furadan) to control pests. Stockists in both districts sold Furadan (in sizes
ranging from 100 g packs to 200 g plastic canisters), with labels in English and Kiswahili, especially
during the planting season. The stockists we interviewed said they were not aware that Furadan
could be used to poison wildlife.
3.6.2 Analysis of environmental sample
The results of the environmental sample analyses demonstrated that carbofuran was used extensively
in the two areas (especially in Laikipia). Elevated concentrations of carbofuran and its two major
metabolites (i.e., 3-hydroxycarbofuran and 3-ketocarbofuran) were detected in the soil, plant and
water samples collected with recoveries in excess of 75%. Analysis of carbofuran metabolites is
very critical to forensic investigations, because they appear to persist longer and can occur in higher
concentrations than the parent compound. This is signifi cant in tropical conditions where carbofuran
dissipation from the site of application can be quite rapid (as previously discussed in Section 3.2).
3.6.2.1 Water residue results
The mean concentrations of carbofuran detected in both Isiolo and Laikipia (i.e., between 0.5 and
495 µg/L in two rivers and below detection level to 2 301 µg/L in ponds and dams close to farms)
were above both the European Union limit (i.e.,1 µg/L) and the US allowable contaminant level (i.e.,
40 µg/L) (Pogacnik and Franko 1999). These levels were also above the maximum concentration
limit (MCL) recommended by WHO for drinking water. As such, these residue levels pose risks
when the contaminated water is used for domestic purposes or as drinking water for agricultural
animals. The solubility of carbofuran in water and its rapid degradability likely account for the
observed decrease in concentration downstream as well as the presence of the two metabolites.
Generally, the results showed a marked increase in the concentration of metabolites from the wet to
dry season. There was also a signifi cant difference (p < 0.05) in mean concentrations of carbofuran
and its metabolites in the wet and dry (sampling) seasons in both districts, though the concentration
of carbofuran and its two metabolites was higher in water sampled from Laikipia.
3.6.2.2 Plant residue results
As a systemic compound, carbofuran is absorbed through the roots and then distributed throughout
various plant organs, mainly the vessels, stems and leaves. As such, it can be detected in the leaves
seven to ten days after application (Crocker 2005). Carbofuran and its two metabolites were detected
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