It is real and significant that climatic changes affect the pesticide behaviour, but there
are no data available on their effect on the pesticide persistence and its pre-harvest
interval (PHI). Therefore, to estimate the potential effect of climatic changes on the
fate of indoxacarb in tomato fruits, the decline rate of indoxacarb residues was
investigated in winter and summer seasons, for three consecutive years under field
condition. Residues of indoxacarb were determined by high performance liquid
chromatography with photodiode array detector (HPLC-DAD). Recoveries were
between 89.5-96.4% with a RSD of 8-15% in tomato at spiked levels of 0.01, 0.05
and 0.1 mg kg-1, respectively. The LOQ of this method was found to be 0.01 mg kg-1
while LOD being 0.005 mg kg-1. Indoxacarb was sprayed on tomato at recommended
dosage. Samples of tomato were collected at 0, 1, 3, 5, 7, 10 and 15 days after
treatment. The decline rates of indoxacarb were described using first-order kinetics.
The results indicated that, the mean half–lives of indoxacarb in tomatoes and PHI
changed significantly through all seasons of the trial. The least half–life time and PHI
were 1.400 and 2.100 d in summer season of 2014, respectively, while the longest
were 2.773 and 4.800 d in winter season of 2012, respectively. Also, a negative
correlation coefficient was observed between the averages of air temperature (of days
after indoxacarb spraying) in seasons of the experiment and the mean half–life times
or PHIs. Whereas a positive correlation coefficient was obtained between averages of
relative humidities and the mean half–life times or PHIs. It was concluded that both
air temperature and relative humidity (as a part of climatic factors) play a great role in
the interaction with indoxacarb persistence and its PHI. This work would be also
helpful for the government of Egypt to establish the MRL of indoxacarb in tomato
and to provide guidance on the proper and safe use of this insecticide. |
