© Benaki Phytopathological Institute
Al-Rajab
et al.
56
imidacloprid were below the MRL direct-
ly after application (2 h) in chickpea pods
and leaves. This difference might be due to
the very low initial concentration of imida-
cloprid (0.29–0.49 mg kg
-1
) in chickpea pods
and leaves. Moreover, imidacloprid residue
concentrations ranging from 0.01 to 0.76 mg
kg
-1
were detected in some fruit and vegeta-
ble samples collected from the Aegean re-
gion in Turkey (Bakirci
et al.,
2014).
The dissipation kinetics of acetamiprid in
qat leaves was similar to that of the other in-
vestigated neonicotinoid insecticide, imida-
cloprid, although the initial concentration
of acetamiprid residues in qat leaves was 3.0
mg kg
-1
, which is 52% less than that of imida-
cloprid. Therefore, its degradation approx-
imated first order (r
2
= 0.95); 37 days after
treatment 8.33% of initial residues remained
in the qat leaves (Tables 2 and 3). The initial
residue concentrations of acetamiprid ob-
tained in this study (3.0 mg kg
-1
) were much
higher than the concentrations reported in
chillies (0.02–0.1 mg kg
-1
) after treatment at
the recommended and double-the-recom-
mended doses (Sanyal
et al
., 2008). A possi-
ble explanation for this discrepancy could lie
in the fact that qat leaves received a higher
amount of pesticide than the chilli peppers
due to their larger surface; consequently,
the concentrations of the chemical in leaves
were found to be higher than those in fruits.
Dissipation of acetamiprid in different
plants has been reported in many recent
studies; however, the literature contains no
information about the dissipation of acet-
amiprid in qat leaves. In our study, the dis-
sipation rate of acetamiprid in qat was rel-
atively slow (half-life = 11.7 days) compared
to that of other plants, such as 1–1.6 days for
the mustard plant (Pramanik
et al
., 2006),
1.8–2.3 days for green-tea shoots (Gupta and
Shanker, 2008), 2.2–4.8 days in chillies (Sany-
al
et al.,
2008), and 1.9 and 2.5 days in zucchi-
ni and zucchini leaves, respectively (Park
et
al.,
2010). Similar to the case of imidacloprid,
no MRL value has yet been established for
acetamiprid in qat, thus, we used its value in
lettuce leaves to compare the preharvest in-
tervals (PHIs). For acetamiprid in lettuce, the
MRL = 3 mg kg
-1
, and the recommended PHI
is 7 days (Global MRL Database, 2015). In the
present study, the residue concentrations of
acetamiprid were below the MRL at 2.6 mg
kg
-1
1 day after treatment (Table 2). Howev-
er, a PHI of 1 day after application is recom-
mended for tea shoots to ensure safe con-
sumption (Gupta and Shanker, 2008); the
PHI of 1 day could be recommended for ac-
etamiprid in qat leaves. Acetmiprid residues
were detected in some fruit and vegetable
samples collected from the Aegean region
in Turkey, but they ranged from 0.01 to 0.06
mg kg
-1
and were therefore below the MRL
value of 3 mg kg
-1
(Bakirci
et al.,
2014).
Despite the relatively high initial residue
concentration of methomyl in qat leaves (12
mg kg
-1
), its dissipation, with a half-life of 5.1
days, was significantly more rapid than that
of imidacloprid and acetamiprid (Tables 2
and 3). The decline of methomyl residues
was very fast after application: About 78.3%
of the residues had dissipated 1 day after
treatment; its degradation then approxi-
mated first order (r
2
= 0.93), and the residue
concentrations at the end of the experimen-
tation, 37 days after treatment, were 0.03
mg kg
-1
. Similar to the case of imidacloprid
and acetamiprid, no value has yet been es-
tablished with respect to the maximum per-
missible intake of methomyl in qat. There-
fore, we used its value in lettuce leaves to
compare the preharvest intervals (PHIs). The
MRL value of methomyl residues in lettuce
is suggested to be 5 mg kg
-1
(Global MRL Da-
tabase 2015). In the present study, the resi-
due concentrations of methomyl, at 2.6 mg
kg
-1
, were below the MRL 1 day after treat-
ment (Table 2); at 5.1 days, its half-life is in
agreement with results obtained by Reeve
et al.
(1992), which showed that variable
half-lives of methomyl in grape foliage in 36
U.S. fields ranged from 1 to 7.7 days. In con-
trast, the half-life of methomyl in qat leaves,
as demonstrated in our study, is longer than
the reported half-lives in other studies of
other plants e.g., 0.9-1.34 days for tomatoes
(Gambacorta
et al.,
2005; Malhat
et al
., 2015)
and 0.88–0.94 days for okra fruits (Aktar
et
al.,
2008). The half-life of methomyl in plants
