MONITORING OF
SOME INSECTICIDE RESIDUES
IN VEGETABLES
AND FRUITS AT THE MARKET LEVEL
L H Lee Fook
Choy and S Seeneevassen
Ministry
of Agriculture, Fisheries and Cooperatives
ABSTRACT
The
amount of some insecticide residues in seasonal vegetables and fruits was monitored at the market level throughout the year 1997. Locally produced vegetables and fruits were
purchased from main urban and rural markets and analysed by gas liquid
chromatography for pesticide residues.
A total of 126 samples of vegetables and 2 samples of fruits were
extracted and analysed for insecticide residues. 115 samples of the vegetable and fruit extracts were analysed for
the presence of the pyrethroid insecticides cyfluthrin, cypermethrin and deltamethrin. 52 samples of the vegetable and fruit
extracts were analysed for the presence of organophosphorus insecticide
dichlorvos, diazinon, fenitrothion, methamidophos, profenofos, phosphamidon,
malathion and parathion. The data
showed that most of the vegetable and fruit samples analysed did not contain
residues of the monitored insecticides above the accepted maximum residue limit
(MRL) as adopted by the FAO/WHO Codex Alimentarius Commission (CAC), although some insecticide residues have been
detected in certain samples only. The
following insecticides have been detected in some of the samples of vegetables
and fruits analysed, but they have been mostly detected below the MRL:
cypermethrin, deltamethrin, methamidophos, profenofos and malathion. The results obtained showed that 61.5% of
the vegetable and fruit samples analysed contained no detectable level of the
monitored insecticides, 36.2% of the samples gave results with levels of
insecticide residues below the MRL, while 2.3% of the samples showed results
above the MRL. Only 3 samples contained
levels of insecticide residues above the MRL.
Keywords : insecticide-residues, residues, insecticides, maximum residue limits, vegetables, fruits, Mauritius.
INTRODUCTION
Pesticides
are chemicals that are utilised by farmers to help them to produce their
crops. Pesticides used in agriculture
include insecticides, fungicides and herbicides. In vegetable and fruit production,
insecticides are used to control pests and fungicides to control diseases. They are directly applied to the crops and
some may still be present as residues in the vegetables and fruits after their harvests. It
is true that insecticides and fungicides are toxic substances, but when used
properly they constitute an important input in vegetable and fruit production
in order to produce economically marketable products.
On the one
hand people are encouraged to consume more vegetables and fruits, these being a good source of
vitamins and fibre and also beneficial to their health - and on the other hand,
the mass media have rightly created an awareness about, but wrongly magnified
the environmental and health problems and the risk involved in the use of
chemicals, especially pesticides, in agriculture. Consequently, this has created a certain apprehension and fear in
the public as to the presence of pesticide residues in their daily food. The
public is confused and alarmed about food safety. The results of a market survey carried out during the year 1997
to determine the level of residues of some insecticides in the seasonal vegetables and fruits available on the local
markets are presented to give a truer picture of the situation.
MATERIALS
AND METHODS
Locally
produced vegetables and fruits were purchased from the main urban and rural markets of the
country throughout the year 1997 and analysed by gas liquid chromatography for
pesticide residues.
The seasonal vegetables and fruits analysed included tomatoes, cabbage,
cauliflower, lettuce, watercress, and beans, golden squash (patisson), mustard
greens (brèdes De Chine), Chinese cabbage (petsai), pineapple and
mandarin. The markets where these
vegetables and fruits were purchased included those of Port Louis, Vacoas,
Curepipe, Rose Hill, Quatre Bornes, Chemin Grenier and Mahebourg. A total of
126 samples of vegetables and 2 samples of fruits (the peel and pulp
separately) were extracted and analysed for insecticide residues by procedures
adapted from methods available in the literature. (Mc Leod and Ritcey 1973;
Thier and Zeumer 1987).
115
samples of the vegetables and fruits were extracted for pyrethroid insecticide residues and these extracts were analysed for the presence of the
pyrethroid insecticides: cyfluthrin (Baythroid),
cypermethrin (Cymbush) and deltamethrin (Decis), using the gas liquid
chromatograph equipped with Electron Capture Detector. 50 samples of the vegetables and one sample
of pineapple were also extracted for organophosphorus insecticide
residues. These extracts were analysed
for the presence of organophosphorus insecticides using the gas liquid
chromatograph equipped with Nitrogen Phosphorus Detector. The organophosphorus
insecticides screened included dichlorvos (DDVP), diazinon, fenitrothion
(Folithion), methamidophos (Tamaron),profenofos (Selecron), phosphamidon
(Dimecron), malathion and parathion.
RESULTS AND
DISCUSSION
The data
showed that most of the vegetable and fruit samples analysed did not contain
residues of the monitored insecticides above the accepted maximum residue limit (MRL) as adopted by the
FAO/WHO Codex Alimentarius Commission (CAC) (1993), although some insecticide residues have
been detected in certain samples only.
The results obtained showed that 61.5% of the vegetable and fruit
samples analysed contained no detectable level of the monitored insecticides,
36.2% of the samples gave results with trace levels of insecticide residues or
levels below the MRL, while 2.3% of the samples showed results above the MRL (Figure
1).
Only 3
samples contained levels of insecticide residues above the MRL. The following insecticides have been detected in some of the samples of vegetables and fruits analysed, but they have been mostly detected below the MRLs:
cypermethrin, deltamethrin, methamidophos, profenofos and malathion.
Details of the amounts of pyrethroid and
organophosphorus insecticide residues detected in the various vegetables and fruits analysed are summarised in Tables
1 and 2.
Figure 1 Insecticide
residues found in
vegetables and fruits samples in
1997
Table1 Pyrethroid insecticide
residues in vegetables and fruits for the year
1997
|
Vegetables
and fruits |
Total
No of samples |
Cypermethrin |
Deltamethrin |
||||
|
Range
mg kg -1 |
No
of samples |
MRL |
Range
mg kg -1 |
No
of samples |
MRL |
||
|
Tomatoes |
15 |
0.01-0.41 |
11 |
0.5 |
0.004-1.07 |
8 |
0.2 |
|
Cabbage |
15 |
0.013 |
1 |
1.0 |
0.017 |
1 |
0.2 |
|
Cauliflower head |
8 |
0.04-0.06 |
2 |
1.0 |
NDL |
|
0.2 |
|
Cauliflower leaves |
8 |
0.47-1.12 |
2 |
1.0 |
0.02 |
1 |
0.2 |
|
Lettuce |
15 |
0.74 |
1 |
2.0 |
0.002 |
1 |
0.5 |
|
Watercress |
16 |
0.02-0.97 |
|
2.0 |
0.003-0.097 |
3 |
0.5 |
|
Beans |
16 |
0.013-0.27 |
5 |
0.5 |
0.011 |
1 |
0.1 |
|
Golden Squash (Patisson) |
14 |
0.014 |
1 |
0.2 |
0.008 |
2 |
0.2 |
|
Mustard
greens (Brede de Chine) |
2 |
0.42 |
1 |
1.0 |
0.084 |
1 |
0.2 |
|
Chinese Cabbage (Petsai) |
2 |
NDL |
|
|
NDL |
- |
|
|
Pineapple (peel) |
1 |
NDL |
|
|
- |
|
NDL |
|
Pineapple (pulp) |
1 |
NDL |
|
|
- |
|
NDL |
|
Mandarin (peel) |
1 |
NDL |
|
|
0.215 |
|
0.05 |
|
Mandarin (pulp) |
1 |
NDL |
|
|
- |
|
NDL |
|
Total |
115 |
|
24 |
|
|
18 |
|
MRL – Maximum Residue Limit NDL – No Detectable Level
It can be seen that the pyrethroid insecticide
residues have been mostly detected in tomatoes, watercress and beans. Cypermethrin has been found in 73% of the
samples of tomatoes analysed, 37% of the samples of watercress and 31% of the
samples of beans, whereas deltamethrin has been found in 53% of the samples of
tomatoes and 19% of the samples of watercress analysed (Tables 1& 3, Figure 2). The organophosphorus
insecticide residues have been detected in trace amounts in a few samples (2
-3) of tomatoes, cabbage, watercress, beans and golden squash (patisson), and
also in the cauliflower and pineapple samples analysed. (Tables
2 & 4, Figure 3)
Figure 2 Frequency of detection of cypermethrin and deltamethrin
in vegetables in 1997
Table 2 Organophosphorus insecticide
residues in vegetables and fruits for the year
1997
|
Vegetables and fruits |
Total No of samples |
Methamidophos |
Profenofos |
Malathion |
||||||
|
Range mg kg -1 |
No of samples |
MRL |
Range mg kg -1 |
No of samples |
MRL |
|
Range mg kg -1 |
MRL |
||
|
Tomatoes |
8 |
NDL |
|
|
0.011-0.076 |
3 |
2 |
|
|
|
|
Cabbage |
8 |
0.008-0.14 |
3 |
1 |
|
|
- |
|
|
|
|
Cauliflower
head |
1 |
0.13 |
|
1 |
NDL |
|
- |
NDL |
|
|
|
Cauliflower
leaves |
1 |
0.14 |
|
1 |
NDL |
|
- |
|
|
|
|
Lettuce |
8 |
NDL |
- |
|
NDL |
|
- |
NDL |
|
|
|
Watercress |
8 |
NDL |
- |
|
0.15-0.28 |
2 |
1 |
|
|
|
|
Beans |
8 |
0.004-0.032 |
2 |
0 |
0.003 |
1 |
|
NDL |
|
|
|
Golden
Squash (Patisson) |
8 |
0.004-0.012 |
3 |
|
|
|
|
|
|
|
|
Pineapple
peel |
1 |
NDL |
- |
|
- |
0.3 |
|
|
|
NA |
|
Pineapple
pulp |
1 |
NDL |
- |
|
- |
NDL |
|
|
|
|
|
Total |
52 |
|
|
|
|
|
|
|
|
|
MRL – Maximum Residue Limit NDL –
No Detectable Level
NA - As an indication, the MRL for other
fruits like Apple is 2, Citrus Fruits is 4, Peach is 6 and Pear is 0.5, all units being in mg per kg
Table 3 Frequency of detection of Cypermethrin and Deltamethrin in vegetables and fruits for the year
1997
|
Vegetables and fruits |
Samples |
||||||
|
Analysed |
Cypermethrin |
Deltamethrin |
|||||
|
Nos |
% |
>MRL |
Nos |
% |
>MRL |
||
|
Tomatoes |
15 |
11 |
73 |
0 |
8 |
53 |
1 |
|
Cabbage |
15 |
1 |
7 |
0 |
1 |
6.7 |
0 |
|
Cauliflower Head |
8 |
2 |
25 |
0 |
0 |
0 |
0 |
|
Cauliflower Leaves |
8 |
2 |
25 |
1 |
1 |
12 |
0 |
|
Lettuce |
15 |
1 |
7 |
0 |
1 |
6.7 |
0 |
|
Watercress |
16 |
6 |
37 |
0 |
3 |
19 |
0 |
|
Beans |
16 |
5 |
31 |
0 |
1 |
6 |
0 |
|
Golden Squash (Patisson) |
14 |
1 |
7 |
0 |
2 |
14 |
0 |
|
Brèdes de Chine |
2 |
1 |
50 |
0 |
1 |
50 |
0 |
|
Petsai |
2 |
0 |
0 |
0 |
0 |
0 |
0 |
|
Pineapple peel |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
|
Pineapple pulp |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
|
Mandarin peel |
1 |
0 |
0 |
0 |
1 |
100 |
1 |
|
Mandarin pulp |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
|
Total |
115 |
30 |
26 |
1 |
19 |
16 |
2 |
MRL
– Maximum Residue Limit
Table 4 Frequency of detection of Methamidophos and Profenofos in vegetables and fruits for 1997
|
Vegetables and fruits |
Samples |
||||||
|
Analysed |
Methamidophos |
Profenofos |
|||||
|
Nos |
% |
>MRL |
Nos |
% |
>MRL |
||
|
Tomatoes |
8 |
0 |
0 |
0 |
3 |
37 |
0 |
|
Cabbage |
8 |
3 |
37 |
0 |
0 |
0 |
0 |
|
Cauliflower Head |
1 |
1 |
100 |
0 |
0 |
0 |
0 |
|
Cauliflower Leaves |
1 |
1 |
100 |
0 |
0 |
0 |
0 |
|
Lettuce |
8 |
0 |
0 |
0 |
0 |
0 |
0 |
|
Watercress |
8 |
0 |
0 |
0 |
2 |
25 |
0 |
|
Beans |
8 |
2 |
25 |
0 |
1 |
12 |
0 |
|
Golden Squash (Patisson) |
8 |
3 |
37 |
0 |
0 |
0 |
0 |
|
Pineapple peel |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
|
Pineapple pulp |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
|
Total |
52 |
10 |
19 |
0 |
6 |
11 |
0 |
MRL
– Maximum Residue Limit
Figure 3 Frequency of detection of methadimophos and profenofos
in vegetables for the year
1997
Details of
the three cases where the MRLs have been exceeded are shown in( Table 5). It is interesting to note that in the sample of cauliflower
leaves where cypermethrin has been found to be above the MRL value (1.0 mg per
kg), the amount of cypermethrin detected in the corresponding cauliflower head
was only 0.06 mg per kg. Similarly in
the mandarin sample under test, the edible pulp contained no detectable level
of deltamethrin, whereas the peel has been found to contain deltamethrin above
the MRL.
Table 5 Pesticide residues in vegetables and fruits
|
Market |
Sample |
Pesticide |
Residue mg kg -1 |
MRL mg kg -1 |
|
Curepipe |
Tomatoes |
deltamethrin |
1.07 |
0.2 |
|
Vacoas |
Cauliflower leaves |
cypermethrin |
1.12 |
1 |
|
Vacoas |
Corresponding Cauliflower head |
cypermethrin |
0.06 |
1 |
|
Curepipe |
Mandarin peel |
deltamethrin |
0.21 |
0.05 |
|
Curepipe |
Corresponding mandarin pulp |
deltamethrin |
NDL |
0.05 |
MRL
– Maximum Residue Limit NDL – No
Detectable Level
The
maximum residue limits (MRLs) have been established for individual pesticide/crop
combinations by the Joint FAO/WHO Meetings on Pesticide Residues (JMPR), using
residue data from supervised trials and uses of pesticides including good
agricultural practices (GAPs) (Anon. 1993). Hence they can serve as an indication for determining whether GAPs
are carried out by the producers. The
MRL is not a toxicity level and has nothing to do with toxicology (Roberts
1991). It is rather 4the level above
which residues should not occur if the pesticide has been used as recommended and
according to GAPs (Roberts 1991).
From our
study only 3 cases have been observed to exceed the MRL. These may be due to non observance of
certain recommended agricultural practices like respecting the safety interval
between the last pesticide application and the harvest of the crop or using the
recommended rate of pesticide application. In order to avoid such occurrences,
the producers should adhere to the recommended, authorised and correct ways of
using pesticides to control pests and diseases in their crops. These chemicals are toxic by nature, but
when used in the appropriate and safe manner as specified on the labels, they
should not be harmful to the user, the consumer or the environment. It is their mis-use, which can be a source
of hazards.
It should
be noted that in this market survey, the vegetables and fruits were analysed as such from the markets, and if cleaned and washed
they should contain less insecticide residues.
Washing of agricultural produce is known to reduce the levels of
residues, which can be dissolved or physically dislodged from the raw product
(Chin 1991). The consumer should also
be aware of the concept of the Acceptable Daily Intake (ADI) in the evaluation
of the safety of pesticide residues in foods.
The ADI of a pesticide is the amount of that pesticide that can be
ingested daily by man during an entire lifetime without an appreciable risk to
the health of the consumer on the basis of all the known facts (Anon.
1993). It is expressed in milligrams
per kilogram of body weight and is obtained from toxicological studies. The ADIs
of some pesticides have been established by the Joint FAO/WHO Meetings
on Pesticide Residues and are published in (Codex Alimentarius – Pesticide
Residues in Food Volume 2 1993 and
1996) (Table 6). So when trace levels
of pesticide residues are detected in our food, this does not mean that it is
unsafe for consumption.
Table 6 Acceptable
daily intakes (ADIs) of some insecticides
|
Compound |
Trade
Name |
ADI
mg kg -1 body
weight |
|||
|
Cypermethrin |
Cymbush
|
0.050 |
|||
|
Deltamethrin |
Decis
|
0.010 |
|||
|
Methamidophos |
Tamaron |
0.004 |
|||
|
Profenofos |
Selecron |
0.010 |
|||
|
malathion |
Malathion |
0.020 |
|||
SOURCE: Codex Alimentarius. Pesticide residues in food –
Maximum residue limits.
Volume 2B. Second Edition. 1996. FAO/WHO
The
concern raised in the public by harmless but detectable trace levels of
pesticide residues in foods is probably overemphasised. It has been pointed out that the hazard to humans from low doses
of substances shown to be rodent-carcinogens has been overestimated (Richardson
1991). It should also be noted that
pesticides could occur naturally.
Plants synthesise a high variety of toxins for their protection against
fungi, insects and animal predators and these natural pesticides occur in very
much larger chemical structure types and at levels sometimes higher than
synthetic pesticides (Richardson 1991).
Some of these natural pesticides have been shown to have carcinogenic
properties, and despite this fact epidemiological evidence suggests that the
intake of vegetables by humans and other animals can and does reduce cancer, e.g. by
ingestion of vitamin C (Richardson 1991).
CONCLUSION
From the
results obtained, it can be concluded that most of the vegetable and fruit
samples analysed did not contain residues of the monitored insecticides above the maximum residue limit (MRL), although some insecticide
residues have been detected in certain samples only. The public therefore should not be concerned about any excessive
amounts of pesticide residues being present in the local vegetables and fruits available on the market.
There were occasional cases where the MRLs have been exceeded. But this can be avoided by inculcating in
the growers, the necessity to strictly follow the recommended and correct ways
of using pesticides.
REFERENCES
ANON. 1993 . Codex Alimentarius. Pesticide
Residues in Food. Volume 2.
Second edition. FAO/WHO, Rome, Italy. p. 3 – 4; p. 461 - 462
ANON. 1996. Codex Alimentarius. Pesticide Residues in Food – Maximum
Residue Limits.
Volume 2B. Second Edition.
1996. FAO/WHO. Rome.
Italy.
CHIN HB. 1991. The effect of
processing on residues in foods: the food processing industry’s residue database. p.
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al. eds. Pesticide Residues and Food
Safety: A Harvest of Viewpoints.
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Chemical Society.
Mc LEOD HA., RITCEY WR. eds.
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and Welfare Canada, Ottawa, Canada.
RICHARDSON
ML. 1991. Epilogue. p.519. In: Richardson M.L. ed Chemistry, Agriculture and the Environment. The Royal Society of Chemistry.
ROBERTS TR. 1991. Pesticides in water – human health, agricultural and
environmental aspects. p. 435. In: Richardson ML. ed. Chemistry, Agriculture and the Environment. The Royal Society of Chemistry.
THEIR H.-P., ZEUMER H. eds. 1987.
Manual of Pesticide Residue
Analysis. Volume 1. p.283- 295.
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