Journal of Tea Science Research. 2015, Vol. 5, No. 9, 1-7
4
Table 3 Kinetics of dissipation of bifenthrin in black tea
Dosage (ml
ha
-1)
Regression equation*
Correlation
co-efficient (r)
Half-life (days)
PHI** (days)
Wet season
1000
2000
Dry season
1000
2000
log y = 0.9477 + (-0.1256) x
log y = 1.2991 + (-0.1171) x
log y = 1.3292 + (-0.1029) x
log y = 1.5640 + (-0.0934) x
-0.868
-0.899
-0.996
-0.989
2.40
2.57
2.93
3.22
1.98
6.21
5.20
10.36
* log y = a + bx; where, y =residue level in mg kg
-1
; x -harvest interval in days & a, b- regression constants
** based on the European Union MRL of 5 mg kg
-1
Table 4 Residues of bifenthrin in tea infusion
Day
Residues of bifenthrin (mg kg
-1
)
Wet season @ 1000 ml ha
-1
Dry season @ 1000 ml ha
-1
Tea Brew
Spent tea
Tea brew
Spent tea
0
1.56
34.38
0.75
16.51
1
0.12
5.49
0.53
15.78
3
BDL
1.53
0.37
9.72
5
BDL
0.84
0.17
5.45
7
ND
0.35
0.15
4.24
10
ND
BDL
BDL
1.79
14
ND
BDL
ND
BDL
the vapour pressure, the loss of pesticides will be
more during the manufacturing process. Owing to
their high thermal stability and low vapour pressure,
pyrethroid pesticides were found to be more stable
during drying than the other pesticides (Jaggi et al.,
2000).
2.3 Transfer of residue from manufactured tea to
infusion and spent leaves
The quantity of bifenthrin residues transferred from
processed black tea to infusion was below 5 %.
While the residues remained in the spent leaves, the
infusion was almost free from bifenthrin at the
recommended rate of application @ 1000 ml ha
-1
.
Generally, only those pesticides with high water
solubility are potentially transferred to the tea
infusion, in significant amounts. The rate of transfer
of the pesticide residues to the infusion depends on
its solubility in water (Nagayama, 1996) and
partition coefficient (Jaggi et al., 2001). Bifenthrin
has very low water solubility (0.1 mg l
-1
), fairly
reasonable octanol-water coefficient (Kow 2,30,000)
and low vapour pressure (1.81 x 10-7 mm Hg at 250
ºC) supported the findings (The Pesticide Manual,
2003). These factors account only for the partial
transfer of residue into brew.
3 Conclusions
The transfer of bifenthrin residues from made tea to
infusion was extremely low. On the basis of the
above findings it can be concluded that at on or after
the 7th day of application, there was no detectable
transfer of residues to the infusion when applied at
the recommended dosage (1000 ml ha
-1
). Thus, the
consumption of tea infusion is safe, when the leaves
are processed after the normal harvesting interval,
after the spraying of bifenthrin. It is confirmed that
the actual consumption of pesticide residues is many
times lower than what is actually present in the
made tea since it is brewed before consumption. It is
