© Benaki Phytopathological Institute
Al-Rajab
et al.
52
venia, Finland, Sweden, Norway, Switzerland
and recently in U.K. (
The Misuse of Drugs
Order, 2014;
EMCDDA, 2016).
The high demand for qat, combined with
the limited amount of cultivated lands, has
raised its value in recent years. Its price has
increased dramatically to approximately
$150–$200/kg, depending on its variety and
origin. An individual chews about 100–300
g of fresh leaves daily (Nakajima
et al.,
2014;
Date
et al.,
2004).
The use of pesticides in qat production is
indispensable in protecting the plants from
different insects and fungi. Consequent-
ly, qat production consumes about 70% of
the pesticides used in Yemen; some of these
pesticides are banned (e.g. DDT) but contin-
ue to be used illegally in the production of
qat and other crops (Date
et al
., 2004). Im-
idacloprid, acetamiprid and methomyl are
the most commonly used insecticides in the
production of qat; some of their key prop-
erties are presented in Table 1. Imidacloprid
(
N
-{1-[(6-Chloro-3-pyridyl)methyl]-4,5-dihy-
droimidazol-2-yl}nitramide; C
9
H
10
ClN
5
O
2
), the
most-used insecticide worldwide, and acet-
amiprid (
N
-[(6-chloro-3-pyridyl)methyl]-
N
’-
cyano-
N
-methyl-acetamidine; C
10
H
11
ClN
4
) are
neonicotinoid insecticides that act as insect
neurotoxins (Sharma and Singh, 2014). Meth-
omyl (
S-
methyl
N
-(methylcarbamoyloxy)
thioacetimidate; C
5
H
10
N
2
O
2
S) is an oxime car-
bamate insecticide used as a broad-spectrum
insecticide since 1968 (Van Scoy
et al.,
2013),
which was banned few years ago but contin-
ues to be used illegally by qat farmers.
Therefore, the consumption of qat might
be an important source of exposure to pes-
ticides, especially because its leaves are con-
sumed fresh, without any thermal treat-
ments that can reduce pesticide residues
(Daba
et al
., 2011). Qat chewing is similar
to the smokeless tobacco chewing among
workers in tea industry in India (Kausar
et
al.,
2014). Moreover, the failure of some local
farmers to respect pesticide labels (dose, ap-
plication method, and post-harvest interval)
might lead to a high risk of qat contamina-
tion by pesticides (Date
et al
., 2004). Results
obtained by Daba
et al.
(2011) showed high
concentrations of the insecticides diazinon
(751 μg kg
-1
) and DDT (1,372 μg kg
-1
) in qat
collected from different farms in Ethiopia. In
contrast, Hassan
et al.
(2013) reported the ab-
sence of pesticide residues in 120 qat sam-
ples collected from Jazan area, Saudi Arabia.
Information on the persistence of pes-
ticides in qat is extremely scarce. The pres-
Table 1.
Structure and key
properties of imidacloprid, acetamiprid and methomyl (Gupta
and Shanker, 2008; Gupta
et al.,
2008; Tomasevic
et al.,
2010; Van Scoy
et al.,
2013).
Compound
M.W.
Solubility
(mg L
-1
)
Log
K
ow
p
Ka
Structure
Imidacloprid
CAS: 3380-34-5
Formula: 5-chloro-2-(2,4-
dichlorophenoxy)-phenol
289.5 4.621
4.7 8.1
Acetamiprid
CAS: 101-20-2
Formula: 3,4,4’- trichlorocar-
banilide
315.6 0.6479
4.9 n/a
Methomyl
CAS: 16752-77-5
Formula: S-methyl N-
(methylcarbamoyloxy)thioa-
cetimidate
162.2 57900
1.24 14
