MSc

An investigation was undertaken to assess the insecticide residues in
market samples of vegetables, viz, bittergourd, cowpea, cucumber and
snakegourd from four markets of Thiruvananthapuram during three seasons
of 1995. The effect of certain decontamination practices on vegetables to
remove residues of insecticides was also assessed.
The study revealed that organophosphate insecticides, VIZ., methyl
parathion, quinalphos, monocrotophos, phosphamidon and phorate were the
contaminants present in the vegetable samples. It was observed that
invariably all the 288 samples collected from the four vegetable markets
/
(Aralumoodu, Chalai, Neduamangadu and Powdikonam) were contaminated
with one or other OP insecticides. The samples collected from Aralumoodu
market during the first season (January-Mar eh) and from Chalai market
during the second season (Apri-May) were found contaminated to a
significantly higher extent than those collected from the other three
markets. The overall analysis of the data on the extent of contamination
revealed that cowpea was the most contaminated vegetable. Forty three
per cent of the cowpea samples were contaminated with OP insecticides
above MRL followed by cucumber (25 0 %), snakegourd (22.3 %) and
bittergourd (16.7 %) Among the five OP insecticides detected during the

survey, methyl parathion was identified as the chief contaminant in cowpea
(0.22 to 0.65 ppm), bittergourd (0.01- to 0.21 ppm) and in snakegourd
(0.04 to 0.52 pp m) whereas phorate was the major contaminant in
cucumber (0.02 to 0.26 pprn).
The overall observation on the insecticide preference of vegetable
growers showed that methyl parathion was the most preferred insecticide



(48.2 %) followed by phorate (18.4 %) The preference for



monocrotophos, phosphamidon and quinalphos were 12 5, 6.9 and 13.8 per
cent respectively.
The pesticide usage data collected from the growers revealed that
95.13 per cent of farmers were using the insecticide at concentrations
higher than the normal, whereas 2.7 per cent of farmers used sub-optimal
concentration, and only two per cent of farmers used the insecticides at
their recommended concentrations. The study also showed that cent per
cent farmers used the spray volumes below the recommended rates (mean
volume of 378 liters / ha as against an optimum volume of 550 to 750 liters
/ ha). Thus use of OP insecticides at higher concentration and at lover
volume of spray was found to be the main reason for higher extent of
illegan residues detected in the survey. Besides frequent application of
insecticides and harvesting at shorter intervals was identified as the reason
for higher insecticide contamination in vegetable cowpea.

The decontamination of the insecticide residue on cowpea showed
that dipping the pods in a 2 per cent solution of salt, tamarind extract, lime
or vineger could remove the phosphamidon residue in the range of 84.9 to
94 per cent and monocrotophos to the tune of 90 per cent. Whereas mere
tap water washing could remove only I 15 per cent of the phosphamidon
residue and 16.83 per cent of monocrotophhos.
Cooking the cowpea samples for 25 minutes (open and closed
cooking) could remove monocrotophos residue in the range of 51.76 to
6105 per cent and phosphamidon residue in the range of 48.36 to 49.41
per cent. Refregeration could remove the monocrotophos to the extent of
17.84 per cent and phosphamidon to the tune of 14.97 per cent.
In bittergourd, dipping the fruit in 2 per cent solution of tamarind
extract, lime, salt or vineger for one hour could remove the monocrotophos
residue to an extent of 90 per cent and phosphamidon to 95 per cent. At
the same time washing the fruit could remove 6.6 per cent of
monocrotophos and 8.78 per cent of phosphamidon.
Cooking the bittergourd fruits for 25 minutes (open and closed
cooking) removed residues of monocrotophos in the range of 52.2 to 54.44
per cent and phosphamidon in the range of 45.05 to 56.04 per cent whereas
sun drying of fruit chips for 2 days removed monocrotophos to the tune of
43.3 and phosphamidon to 24.17 per cent Refrigeration of fruits could
remove 8.33 per cent of monocrotophos and 16 per cent of phosphamidon
residues.