PhD

An investigation on the fate of carbofuran applied to the soil basin of
black pepper (Piper nigrum L.) was conducted during 1992-1995 at the College of
Horticulture, Vellanikkara. Laterite soils collected from the predominant pepper
growing tracts of Kannur and Wayanad of Kerala state were used for the study. A
field study was also conducted at the KADP farm attached to the College of
Horticulture, Vellanikkara.
The sorption of carbofuran in laterite soils and its persistence, influence
of organic matter on the bio-availability of carbofuran, mobility of the insecticide in
soil under field conditions and the effect of carbofuran on the growth of black
pepper were assessed. The main findings of the study are given below.
The sorption of insecticide in soil was found to be explained by
Freundlich adsorption equation. The rates of sorption of carbofuran was not
influenced by the organic matter contents .
. An initial lag period was observed prior to carbofuran degradation in soil
under laboratory conditions. Only one metabolite (3-hydroxycarbofuran) was
detected as the product of degradation.
The total content of 14C derived radioactivity was high in plants grown
in soils with lowest organic matter content and vice versa. Hence, bioavailability of
the insecticide is less in soils with high organic matter contents. So a discriminatory
application of carbofuran is required depending on organic matter content of the soil.
Thus for effective control of the pest in a soil with high organic matter content more

quantity or carbofuran has to he applied than a soil with low content of organic
matter.
The residues of 14C-carbofuran absorbed plants left after HCl extraction,
retained significant amounts of radioactivity which could be recovered following
combustion. This indicated that determination of extraction efficiency by spiking or
fortification of the samples with known quantities of insecticides would lead to
overestimation of the recovery.
The main metabolite of the carbofuran in the leaves was 3-hydroxy-
carbofuran.
Autoradiography of the bush pepper plants which was allowed to absorb
14C-carbofuran for 6 h showed that carbofuran was absorbed and translocated to the
leaves and berry.
Both carbofuran and hydroxycarbofuran were leached to the lower layers
of soil (0-60 cm) during SW and NE monsoons. The content of hydroxycarbofuran
was less than carbofuran in soils.
In the foliage and berries carbofuran and the metabolite, 3-hydroxy-
carbofuran accumulated. The content of hydroxycarbofuran was greater than that of
carbofuran. As the harvesting time was delayed the content of residues also
decreased. The early harvesting and use of immature berries may lead to more
concentration of pesticide in the produce. This will lead to chances of more residue
build-up in the human system.