PhD

The study entitled “Dissipation and distribution of fipronil and carbosulfan and their
metabolites in banana (Musa spp) and soil” was carried out at the Department of Soil Science
and Agricultural Chemistry, College of Agriculture, Vellayani during the period from
August 2016 to April 2017. The objective was to assess the dissipation, metabolism and
persistence of fipronil and carbosulfan in banana, cv. Nendran (AAB), grown under red loam
soils (AEU 8-southern laterites) of College of Agriculture, Vellayani, and its impact on soil
organisms.
Banana variety Nendran, grown as per package of practices recommendations, KAU
in randomized block design at the Instructional Farm, Vellayani, with five treatments viz.,
T1- absolute control (No application of carbosulfan and or fipronil), T2- recommended
practice of 30 mg ai of fipronil per plant per application, applied 3 times on 0, 60 and 150
days of planting, T3 – double dose of T2, T4- recommended practice of 400 mg ai of
carbosulfan per plant per application, applied 3 times on 0, 60 and 150 days of planting and
T5- double the dose of T4. Samples viz, soil, leaves, fingers bunches and flower bud, central
core of pseudo-stem and corm were collected and analyzed for residue at definite time
intervals.
The residue estimation of the target pesticide molecules and their toxic metabolites
were performed by adopting standard extraction and clean up procedure viz., conventional
acetone extraction followed by hexane partitioning as well as by QuEChERS method.
Method validation was conducted by spiking with analytical standards from which recovery,
(accuracy 70-120% of spiked values), standard deviation of recoveries, RSD value (below
20%), linearity (calibration curve), for the adopted method were worked out and compared
for compliance. Acetonitrile extracted samples were analyzed using “Waters Acuity UPLC
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system” with suitable column and then subjecting the effluent to triple quadrupole API 3200
MS/MS system equipped with electrospray ionization interface (ESI) operating in required
mode as per the molecule. Extraction using QuEChERS method gave satisfactory values for
validation parameters and hence adopted for the studies.
The presence of carbosulfan in the 1st to 4th leaves till day 20th and subsequent
dissipation pattern prediction for BDL in 22.5 day indicated that, at recommended dose of
application, it is not safe to use the leaves within 23 days of application for serving or food
packing (as commonly practiced in many households of Kerala).
Sample matrices revealed the presence of metabolites each for fipronil and
carbosulfan with variation from below detectable limit (BDL) to a highest content of 3.804
μg/g carbosulfan at 2 hours of application in the soil. Blossom bud, flower bract alone, bunch
on 15th day of emergence, bunch on 30th day of emergence, peel, bunch on harvest, pseudo
stem and corm did not register any detectable level of fipronil or carbosulfan and their
metabolites and even with an additional application of treatment on the day of bunching
also did not register any detectable level of fipronil or carbosulfan and their metabolites.
Residue of fipronil and their toxic metabolites in the first, second and third leaves of
banana on penultimate day of completion of pre-bunching application was found to be below
the detectable levels throughout the period of sampling and this may be attributed to low
absorption, fast metabolism and mobility. However, on 40th day the fipronil was detected in
the 4th leaf to the extent of 0.034 μg g-1 and was not detectable on 50th day.
Metabolites of Carbosulfan residue existed in the first, second and third leaves
between 5th and 20th day and it dissipated to below detectable limit on 40th day of application.
The content of residue under treatment T5 was distinctly higher than T4 during these periods
and dissipated to BDL on 25th day.
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In soil, the fipronil though dissipated to BDL before 50th day, persisted from 2 hours
of application till 40th day. However, carbosulfan and its metabolites were early to dissipate
to BDL on 7th day of completion of application. Sample in experiment with 5 times the
recommended dose of application as injection into pseudostem at the time of bunch
emergence also did not record any residue above detectable level in the flower bud, flower
bract alone, bunch on 15th day of emergence, bunch on 30th day of emergence, peel, bunch
on harvest and pseudostem.
Soil urease activity on 10th day was significantly influenced by the treatment where
T1, T3 and T5 are significantly lower than T2 and T4. However, dehydrogenase activity and
acid phosphatase activity were not significantly influenced by the treatment. Bacterial
population was higher in T1. Treatments were found to significantly influence the weight of
blossom bud on dehorning, pseudostem, bunches and corm. Other biometric parameters
were not influenced by the treatment.
The above results show complete dissipation of fipronil and carbosulfan to safe limits
in soil and banana leaf, when applied as per package of practices recommendation for banana
cultivation (fipronil 30 mg a.i. and carbosulfan 400 mg a.i. per plant applied thrice viz., on
0, 60 and 150 days of planting), within 50 and 23 days of application. Also, the application
of fipronil and carbosulfan as per the above dose in no way results in the accumulation of
residue on any of the edible plant parts of banana and hence it is safe for human consumption.