Environmental Engineering Reference
In-Depth Information
Table 3.4
Physicochemical properties of carbofuran and its fate in Kenyan soils compared with
other commonly used insecticides
Physico-chemical property
Carbofuran
DDT
Malathion
Lindane
Molar mass (g/mol)
Water solubility (mg/L)
Vapour pressure (mbar)
Log K
ow
Melting point (°C)
DT
50
(days) in Kenyan soils
DT
50
(days) (Furadan) non-fl ooded
soil
Soil bound residue formation %
(range)
Soil bound residue formation
(Furadan) %
Freundlich constant K
f
(range)
Kenyan soil
Freundlich constant 1/n (range)
Kenyan soil
K
OC
% leachate (48 hr standard
leaching test)
Acute oral LD
50
birds mg/kg body
weight
24 hr LC
50
fi sh
Oreochromis niger
mg/L
221.3
700
2.6
10
5
1.23
1.42
147
66
96.3
115.5
354.5
1.2
10
3
1.7
10
7
4.98
108.5
64
110
NA
330.4
145
1.6
10
4
2.36
285
36.7
770
NA
219
7.0
1.7
10
4
5.23
112
5
8
NA
9.0
52.7
0.16
5.9
2.2
11.4
0.19
6.0
9.6
48.1
NA
NA
NA
1.5
1.7
ND
1.7
1.8
ND
1.0
ND
0.70
0.81
ND
22
29
33
2.45
10
5
ND
291
2.2
37.8
1.1
10
3
ND
1.65
840
2.24
10
3
100
1.49
10
3
75
2
10
3
0.225
*0.002
0.042
*0.06
10.7
**0.02
NA: not applicable
ND: not determined
DT
50
: half-life
'LC
50
'denotes 'lethal concentration to cause 50 percent mortality in study group,
*
96 hr LC
50
in various species
**
NOEC, 'no observed effect concentration' in fi sh
References
:
Lalah and Wandiga (1996b); Lalah, Kaigwara, Getenga et al. (2001); Wandiga, Lalah and Kaigwara (2002)
Kenyan soils and factors that infl uence carbofuran interaction and disappearance from tropical soils
can be found elsewhere (e.g., Lalah, Kaigwara, Getenga et al. 2001). Other factors, such as soil pH,
also play a role in adsorption/desorption (Haque 1975; Calderbank 1989).
Signifi cant residues of carbofuran and its metabolites (3-ketocarbofuran and 3-hydroxycarbo-
furan, see Figure 1.9, Chapter 1) were recently detected in unfl ooded agricultural soils in Laikipia
and Isiolo, where Furadan was applied to control pests in maize (Otieno 2009, and see Section 3.6).
Laboratory and fi eld studies carried out at the Ahero Irrigation Scheme, where carbofuran has been
extensively applied in rice paddies since the 1980s, showed that the compound readily degrades in
both unfl ooded and fl ooded soils to yield several breakdown products including: 3-ketocarbofu-
ran, 3-hydroxycarbofuran, carbofuran phenol, 3-hydroxycarbofuran phenol and 3-ketocarbofuran
phenol. Most of the residues were detected within the top 10 cm layer in fl ooded soils (Lalah and
Wandiga 1996a) where they would also be available to fi sh, birds and other aquatic organisms. A more
detailed discussion of the leaching and retention rates of carbofuran (and metabolites) in Ahero and
Chiromo soils can be found in Lalah and Wandiga (1996a).
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