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. 177.  In: .  Tweedy B.G. et al.  eds.  Pesticide Residues and Food Safety:  A Harvest of Viewpoints.  Washington DC, USA:  American Chemical Society.

 

Mc LEOD HA., RITCEY WR.  eds.  1973.  Manual on Analytical Methods for Pesticide Residues in Foods.  Health Protection Branch.  Health 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. Deutsche Forschungsgemeinschaft. VCH Verlagsgesellschaft, Weinheim, FRG.