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Processing effect on pesticide residues in food crops 379
EFFECT OF PROCESSING ON PESTICIDE RESIDUES
IN FOOD CROPS - A REVIEW
Anwaar Ahmed*, Muhammad Atif Randhawa**, Muhammad Javed Yusuf***
and Naeem Khalid****
ABSTRACT
The use of pesticides is inevitable to control the pests in different crops, fruits
and vegetable plants. It is increasing day by day in Pakistan. The persistent use
of pesticides leaves behind toxic residues on food crops. These pesticides
upon ingestion exert adverse effects on human health, in addition to disturbing
ecosystem. The organochlorine, organophosphorus, carbamates and
pyrethroid pesticides have been detected in samples of fruits and vegetables
collected from various locations of the world especially in Indo-Pakistan. Most
of the samples contained toxic residues exceeding maximum residues limits.
Experiments have been carried out to determine the reduction in pesticide
residues due to various processing techniques like washing, peeling, frying,
freezing and cooking of fruits and vegetables. Likewise treatment of food crops
with acidic or alkaline solution also minimized the pesticide residues. This
paper reviews the literature published upto the year 2009 focusing on the
injurious effects of pesticides and their degradation by processing and
chemical treatment. In this literature, it is suggested that different processing
operations can be effectively applied on fruits and vegetables to minimize the
risk of pesticides on human health.
KEYWORDS: Pesticides; residues; food crops; toxicity; Pakistan.
INTRODUCTION
In Pakistan, crop losses are very alarming which are estimated as 30-40
percent pre-harvest, 10-30 percent post harvest and 50 percent crop losses
are due to insects, weeds, diseases and rodents (21) In order to safeguard
agricultural produce from ravage of pests, use of pesticides is considered as
*Assistant Professor, Department of Food Technology, Pir Mehr Ali Shah Arid
Agriculture University, Rawalpindi, Pakistan, **Assistant Professor, National Institute of
Food Science & Technology, University of Agriculture, Faisalabad, ***Assistant Botanist,
Fodder Research Institute, Sargodha, Pakistan, ****Deputy Secretary (Planning),
Department of Agriculture, Govt. of Punjab, Lahore, Pakistan.
J. Agric. Res., 2011, 49(3)
A. Ahmed et al.
380
the only solution. Due to reason, pesticides consumption has increased
manifolds during the last two decades (29). Most of the growth in world
pesticide market is in developing countries. Globally, organophosphates
account for nearly 40 percent of total insecticide sales by value followed by
carbamates (20.4%), pyrethroids (18.4 %) and organochlorines (6.1%) (4).
Pakistan is importing a huge quantity of pesticides every year. In 1990, it
imported 13030.14 tons of pesticides; which reached to 30479.00 tons in
1995. During year 2007 the import increased to about 41406.00 tons. So the
import of pesticides is increasing day by day in the country (39).
Pesticide a necessary evil and its injudicious use
Sulfur was used as pesticide to control insects and mites 5,000 years ago. In
ancient times, Chinese used mercury and arsenic compounds to control body
lice and other pests while Greeks and Romans used oil, ash, sulfur, and other
materials to protect themselves, as well as livestock, and crops from various
pests. The cultural methods were also employed to control the pests, such as
crop rotation, tillage and manipulation of sowing dates (12).
The modern era of chemical pest control began around the time of World
War-II, when the synthetic organic chemical industry began to develop. The
first synthetic organic pesticides developed were organochlorines, such as
dichlorodiphenyltrichloroethane (DDT) in Switzerland in 1939. The DDT and
other organochlorine insecticides (cyclodiene organochlorines, aldrin and
dieldrin, endrin, endosulfan and isobenzan) were used as these insecticides
acted against insects by blocking their nervous system, causing malfunction,
tremors, and death (42). Hence, pesticides application became an essential
component of modern agriculture. Although the wide-spread use of pesticides
in Pakistan has controlled the pests, but like other countries, it has started
causing environmental problems in the area. In some areas of Punjab and
Sindh groundwater has been found contaminated and is constantly being
contaminatied due to pesticide use. There is considerable evidence that
farmers have overused and misused pesticides especially in cotton-growing
areas. It is evident from the biological monitoring studies that farmers are at
higher risk for acute and chronic health effects associated with pesticides due
to occupational exposure (39). However, pesticide use also has created
concerns regarding its effect on the environment and the potentially toxic or
carcinogenic residues remaining in the food chain (27).
J. Agric. Res., 2011, 49(3)
Processing effect on pesticide residues in food crops 381
Toxicity of pesticides
Deaths from exposure to pesticides are not uncommon. Each year thousands
of farmers, especially in developing countries, are affected by exposure to
pesticides especially those living near the farms. Recent estimates quoted by
Food and Agricultural Organization (2000) from Pesticide Action Network
(PAN) show that approximately three million people are poisoned and
200,000 die from pesticide poisoning each year. The largest number of
deaths occurs in developing countries. For example, hospital statistics in Sri
Lanka show that on average 14,500 individuals were admitted to government
hospitals and around 1500 individuals a year died from pesticide poisoning
during the period 1986–1996 (National Poisons Information Centre, 1997).
However, these figures should be interpreted with caution. It should be
pointed out that not all hospital admissions and deaths were due to
occupational poisoning but include cases of self ingestion (suicides),
accidental ingestion and homicides. Moreover, there is evidence suggesting
that some pesticides can produce immune dysfunction among animals when
exposed to pesticides (40). A study (16) showed that women who had
chronically ingested groundwater contaminated with low levels of aldicarb had
significantly reduced immune response, although these women did not exhibit
any overt health problems. However, it should be noted that study of immune
suppression potential for pesticides is still in its infancy and that the evidence
available is inconclusive (40). Even in developed countries, despite the strict
regulations and use of safer pesticides, occupational exposures may be
significant (4). It is believed that in developing countries incidence of pesticide
poisoning may even be greater than reported due to under-reporting, lack of
data and misdiagnosis (17).
The incidence and severity of ill health from pesticide-use are far greater in
developing countries than in developed countries due to many reasons. Most
of the farmers in developed countries use pesticides from a closed
environment such as an aircraft or a tractor, while farmers (who are largely
small scale farmers) in developing countries use hand sprayers, thus
increasing the incidence of direct contact with pesticides. Moreover, as noted
by WRI (4) farmers in the developing world use more insecticides, they use
them more frequently and also apply insecticides that are more toxic than
those used in developed countries. Inadequate education, training and
pesticide regulations in the use of pesticides lead to accidents, haphazard
application and over-use. Access to medical treatment is limited and most
farmers rely on homemade remedies thus increasing the severity and
duration of illnesses. Poor health and diet are other factors that are believed
to increase the incidence of illnesses from exposure to pesticides in
J. Agric. Res., 2011, 49(3)
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382
developing countries (4). Inadequate or non-existent storage facilities, poor
living conditions and water supplies contaminated with pesticides also affect
the health of families.
Pesticide residues in raw fruits and vegetables
The organochlorine, organophosphorus and pyrethroid pesticides were
monitored in samples of fruits and vegetables procured from the whole sale
market of Karachi during July 1988 and June 1990. A total of 250 samples
were screened out of which 93 samples were found to be contaminated with
variety of pesticides. Forty five samples were found to contain residues above
maximum residues limits (MRLs) proposed by FAO/WHO while 48 samples
contained residues well within permissible limits. In remaining samples, no
pesticides residue was detected (39). In 2001 a total of 315 samples
representing a wide variety of produce were tested. Of these 73 percent
samples were fresh produce and 27 percent were processed foods. Pesticide
residues were found in 47 percent samples of fresh produce and 7 percent of
processed foods samples (41). Frank et al. (18) surveyed Ontario grown
vegetables in Canada for pesticide residues during 1980-85. A total of 354
samples were screened. Most of the samples contained residues well within
maximum residues limits (MRLs) while the limits were exceeded in only a
small number of samples. In 1998 a total of 180 samples of vegetables were
tested, 89 percent were fresh produce and 19 percent were processed
vegetables. Pesticide residues were found in 35 percent of fresh produce
samples and 10 percent of processed vegetables (39, 41).
EFFECT OF PROCESSING ON PESTICIDE RESIDUES
Experiments were carried out to determine changes in pesticide residues due
to washing, peeling and cooking process (blanching and frying). The purpose
of these experiments was to assess the stability of pesticides in vegetables
and their products. There are strong evidences that through processing of
vegetables pesticide residues decrease (25, 33, 34, 37). Unit operations in
processing typically include washing the raw product with large volumes of
water, frequently using high-pressure sprays and often incorporating
surfactants or other washing aids; peeling the product mechanically with
knives, abrasive disks, or water; blanching with hot water or steam; and in
case of canned or cooked foods, cooking of the product at temperatures at or
above the boiling temperature of water. Thus, residue that may be present
was subjected not only to physical removal by washing or peeling but also
acid or base hydrolysis and thermal degradation (11).
Washing
J. Agric. Res., 2011, 49(3)
Processing effect on pesticide residues in food crops 383
Surface residues are amenable to simple washing operations whereas
systemic residues present in tissues will be little affected. For example, highly
pola and systemic methamidaphos was the only pesticide whose residues
could not be removed from field tomatoes by washing. There is evidence for a
variety of crops and pesticides that the proportion of residue that can be
removed by washing declines with time (19, 33, 34, 36, 37). This has been
interpreted as being due to residues tending to move into cuticular waxes or
deeper layers. For example the fractions of fenitrothion or methidathion
residues on cauliflower that could be removed by washing or blanching were
inversely proportional to the days after spray application (38).
Hot washing and blanching are more effective than cold washing and the
effectiveness may be further improved by detergent (19). Blanching removed
82 percent of methidathion residues from cauliflower and did not show any
effect of withholding period as compared to the lower proportion of residues
removed by washing (30). Domestic rinsing is less effective compared to
thorough commercial washing. Hot caustic washes used in some commercial
peeling operations can efficiently remove and degrade residues of
hydrolysable pesticides (15).
Peeling, hulling and trimming
The majority of insecticides or fungicides applied directly to crops undergoes
very limited movement or penetration into the cuticle. Therefore, residues of
these materials are confined to the outer surfaces where they are amenable
to removal in peeling, hulling or trimming operations (20, 35). Peeling fresh
fruits such avocado, bananas, citrus, kiwifruit, mango and pineapple achieves
virtually complete removal of residues from the fruit. There is substantial data
showing non-detectable residues in pulp of citrus and edible portion of other
fruits that support these conclusions. For example, supervised field trials of
pirimiphos-methyl on various citrus crops gave non-detectable (< 0.03 mg/kg)
residues in the pulp compared to residues in the peel (0.5 to 5 mg/kg) (5).
Post harvest dipping trials were conducted on pineapple with the fungicide
triadimefon which has some trans-laminar action. Residues in the flesh were
only 0.5 to 1 percent of those in the peel (20). Under Codex, MRL’s are based
on the whole fruit which is appropriate for assessing compliance with Good
Agricultural Practices (GAP) (39). These MRLs are of limited significance in
assessing exposure to pesticides from consumption of fresh fruits which are
peeled or juiced. However, apples and tomatoes may be consumed either
whole or after peeling.
J. Agric. Res., 2011, 49(3)
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384
Residues of systemic pesticides can enter the flesh of crops. Following early
season soil incorporation of phorate, residues in washed whole potatoes of
0.37 mg/kg (parent plus oxidation products) were reduced only by 50 percent
through peeling (5). Similarly disyston residues in potatoes were reduced only
35 percent by peeling (8) whereas residues of the much more lipophilic
chlorpyrifos were completely removed in the peels (24). The hulls of cereal
grains generally contain the majority of pesticide residues from any field
treatments. Residues of parathion in oat or rice grains were reduced eight
folds on hulling (5). Pirimiphos methyl residues in rice were reduced 70
percent and 90 percent by husking and polishing, respectively (13). Husking
of corn (maize) removed 99 percent of the residues from field treatments with
tetrachlorvinphos (14).
Cooking and canning
The processes and conditions used in food cooking are highly varied (25).
The details of time, temperature, degree of moisture loss and whether the
system is open or closed are important to the quantitative effects on residue
levels. Rates of degradation and volatilization of residues are increased by
the heat involved in cooking or pasteurization. For example, in a study on
radio labeled chlorothalonil residues, cooking under open conditions resulted
in 85 to 98 percent losses by volatilization. Cooking under closed conditions
resulted in hydrolysis with 50 percent of the chlorothalonil being recovered
unchanged on the crop and hydrolysis product being found in the liquor (5).
For compounds that are of low volatility and relatively stable to hydrolysis
such as DDT and synthetic pyrethroids, losses of residues through cooking
may be low and concentrations may actually increase due to moisture loss.
However, deltamethrin has been reported to have a half-life of 9 minutes in
boiling water and residues were reduced by 66 percent by cooking of various
vegetables (10).
Commercial processing in its various forms combines elements of washing,
peeling, juicing, cooking and concentration. Processing of whole tomatoes
with vinclozolin residues of 0.73 mg/kg gave residues in canned juice, puree
and ketchup at level of 0.18, 0.73 and 0.22 mg/kg, respectively (5, 25). In this
case the relatively stable fungicide vinclozolin was carried through the
process in significant amounts. Only 13 percent of parathion residues on
tomatoes were found in canned juice or ketchup.
Stir-frying and freezing
Pesticide residues can be effectively decreased by stir-frying (32, 45). These
can be reduced upto 49 and 53 percent by peeling and frying (33). Freezing
J. Agric. Res., 2011, 49(3)
Processing effect on pesticide residues in food crops 385
of food is a common method of food preservation which slows both food
decay and most chemical reactions. Freezing of tomatoes decreased the
pesticide residues from 5 to 26 percent after six days and 10 to 31 percent
after 12 days of pesticide contamination (1). Zhang et al. (45) estimated the
pesticides residue levels in cabbage after preserving in refrigerator. In some
vegetables, pesticide residues are decreased after refrigeration. By
increasing the time of refrigeration there is gradual increase in reduction of
pesticide residues, After three days of freezing, HCB, lindane, DDT,
dimethoate, profenofos and pirimiphos-methyl decreased by 4.91, 6.32, 4.07,
13.0, 11.5 and 9.35 percent, respectively (15).
EFFECT OF CHEMICAL SOLUTIONS ON PESTICIDE RESIDUES
Acidic solutions
Soaking in acidic solution like citric acid, ascorbic acid, acetic acid and
hydrogen peroxide at a concentration of 5 and 10 percent for 10 minutes
indicates proficient reduction of pesticide residues. Acidic solutions give more
pesticide dissipation than neutral and alkaline solutions. The acidic solutions
of 5 and 10 percent eliminated pesticide residues completely while, citric and
ascorbic acid solutions of 5 and 10 percent eliminated pesticide residues upto
80 percent (43). Some other scientists (14, 31, 36) also reported that partial
removal of residues was affected by the washing operation (water and/or
acetic acid, sodium chloride).
Neutral solutions
Sodium chloride (NaCl) solution is largely used to decontaminate the
pesticide residues from different fruits and vegetables. There are several
studies (14, 31, 36, 46) to prove the efficacy of salt water washing for
dislodging the pesticides from fruits and vegetable surfaces. In this process,
samples of chopped fruits and vegetables were put in a beaker containing 5
and 10 percent NaCl solution for 15 minutes. The samples were gently
rubbed by hand in salt solution and water was decanted. Twenty eight to 93
percent reduction in organochlorines and 100 percent organophoshates
removal was achieved by using 5 and 10 percent NaCl solution (43). The
percentage reduction in pesticide residues increases with the gradual
increase in concentration of solutions (1, 22). NaCl with 2, 4, 6, 8 and 10
percent solution caused 20 to 90 percent reduction in pesticide residues.
Similarly 18 to 65 percent loss in pesticide residues was reported by Soliman
(37) by using 2, 4, 6, 8 and 10 percent acetic acid solution.
J. Agric. Res., 2011, 49(3)
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386
Alkaline solution and ozonation
Solutions of NaOH, acetic acid, potassium dichromate and soap are used as
decontaminating agents. Dipping of fruits in NaOH solution removed 50 to 60
percent surface residues of pyrethroids compared to 40 to 50 percent
removal by hydrolytic degradation with NaOH and a detergent solution
removed 50 to 60 percent residues (6).
Ozone because of its powerful oxidizing property is effectively applied in
drinking water and waste water treatment. Recently some scientists found
that certain pesticides like 2, 4-dichlorophenoxyacetic acid, carbofuran,
phorate, chlorophenylurea, can readily be degraded in aqueous solution by
ozone (7, 9, 26). Ozonation is a safe and promising process for the removal
of pesticides from aqueous solution and vegetable surface under domestic
conditions. Tap water treatment alongwith ozonated water treatments
significantly reduced the pesticide residues on vegetables, as compared to
no-wash treatment (41).
CONCLUSION
From the extensive review on the use and fate of pesticides during food
processing, it is concluded that pesticides are inevitable part of the agriculture
but their indiscriminate use can cause serious health problems. In a
developing country like Pakistan there is a great need to regulate the use of
pesticides where the extensive use of pesticides is causing serious health
and alarming environmental problems. To minimize the risk of pesticides on
health different processing operations are applied on fruit and vegetable
crops that reduce the pesticide residues below the risk level. It is further
concluded that treatment of vegetables with acidic and alkaline solutions can
effectively minimize the pesticide residues. There is a need to educate the
consumers through media.
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