Journal of Tea Science Research. 2015, Vol. 5, No. 9, 1-7
2
with bifenthrin 8 SC @ 1000 and 2000 ml ha
-1
.
2 Results and discussion
2.1 Recovery of bifenthrin from black tea
The analytical method was validated for black tea
and fresh green leaves prior to actual analysis. To
validate the analytical method, recovery percentage
was established by fortification of technical standard
solutions of bifenthrin from black tea samples,
control tea sample of 20 g was fortified with 0.944
mg l
-1
(by adding 2 ml aliquot of 9.44 mg l
-1
standard bifenthrin solution in hexane) replicated six
times separately. After mixing and allowing the
solvent to evaporate, the samples were analyzed for
the concentration of bifenthrin residue as described
earlier. The recovery obtained was 94.93 % at 0.944
mg kg
-1
level of fortification and a recovery of
91.70% at 0.0944 mg/kg level all of which show a
clear validation to the procedure adopted for
extraction and analysis of bifenthrin residues from
tea samples.
Recoveries of the pesticide at different fortification
levels, i.e. 0.01, 0.1, 0.2 and 0.5 µg ml
-1
were
determined in three replicates from each matrix to
validate different analysts and evaluate the accuracy
of the method.
2.2 Persistence of bifenthrin in black tea
The residues of bifenthrin in black tea at Gudalur
and Valparai when applied @ 1000 and 2000 ml
ha-1 during wet and dry season at different harvest
intervals are given in the Table 2.The residue level
of bifenthrin in black tea when the formulation
bifenthrin (Brigade 8 SC) was applied @ 1000 and
2000 ml ha
-1
during wet and dry seasons
exponentially dissipated after spraying and reached
below the MRL of 5 mg kg
-1
, prescribed by
European Union, on 7th day after application at the
recommended dosage of 1000 ml ha
-1
in Gudalur
and Valparai. Based on the above data, half life, the
pre-harvest interval (PHI) after application of
bifenthrin in tea could be fixed as 7 days (Table 3).
Studies on the infusion indicated that bifenthrin
residues did not leach into the tea brew (Table 4).
Linda & Hooper (2002) reported the degradation of
bifenthrin on several substrates. Gu et al. (2008)
studied the persistence and dissipation of synthetic
pyrethroids in red soils from the Yangtze River delta
area. Data are also available on the degradation and
persistence of synthetic pyrethroids in tropical soil
and aquatic environment (Awasthi, 1997). In tea
fields, besides the effects of some physical and
chemical factors like light, temperature, pH,
moisture, degradation of insecticides, growth
dilution might have played significant role and
rendered bifenthrin residue unavailable in short a
period. Half-life of 0.52 – 0.77 days was reported by
Chen & Wan (1988) for bifenthrin in tea. They
further reported that the other pyrethroids such as
cypermethrin and permethrin also had similar half
lives in tea. Growth dilution is an important factor in
reducing the residue levels in tea crop as the shoots
on which pesticides are applied, are in different
stages of growth (Agnihothrudu & Muraleedharan,
1990; Bisen & Ghosh Hajara, 2000; Chen & Wan,
1988). The weight of these immature shoots increase
during growth, depending on the plucking interval.
The immature buds, by the time they attain the size
of pluckable shoots, the residues of applied
pesticides on them will undergo a growth dilution.
Loss of residues ranging from 40 to 45%,
specifically of pyrethroid group of chemicals due to
growth dilution had also been reported (Xue & Chen,
1992). A rainfall shortly after the application plays a
significant role in washing of applied pesticides
(Chen & Wan, 1997) and might be the major reason
for faster dissipation of residues in wet season as
observed in the present study (Table 1). The present
findings support the dissipation behavior of
bifenthrin residues in tea during wet and dry
conditions (Tewary et al., 2005). Withering of tea
leaves was a major reason for total degradation. This
might be due to evaporation during withe ring
process. Chen & Wan (1988) reported 30 to 60 per
cent of reduction in pesticide residues during
processing, especially during drying. After higher
