Author: Habel parwaiz, Muhammad Danyal Khan, Norman Javed Gill and Tahawar Ali syed
Department of Entomology University of Agriculture Faisalabad
When a crop is treated with a pesticide, a very small amount of the pesticide, or its metabolites or degradation products, can remain in the crop until after it is harvested. For import and export of food commodities there is standard fix by World Trade Organization in form a standard MRL (minimum residue limit) values for each and every crop which is being imported or exported should below this MRL value which tested by quarantine department of desire country or region who are going to import or export. Ultimate purpose of this standard to ensure safe food regulation to all regions and countries of the world.
How pesticides turn up in our food
Used by farmers for following purpose:-
-To control the growth of weed
-Prevent crop damage by insects, rodents and molds.
-Used on food crops after harvest to prolong their storage life.
-used on animal farms to control insect pests
Harmful effects of pesticides residues to the environment
-Water system get polluted
-Pollute the air by evaporating
-Harming beneficial insect species (pollinators, Predator, Parasites, scavengers, etc.)
– Harming soil beneficial fauna (worms, nematodes, mites, micro-organism, etc.)
-Weakening plant root system and immune system
Health hazards from pesticide residue
-Above the tolerance level harmful to human beings.
-Like the neurological and psychological problems.
-Chronic toxicities cause by pesticide.
– Long term effect like cancer, reproductive effects, etc.
-Acute effects abdominal pain, dizziness, headaches, nausea, vomiting, skin and eye problem.
Processed food have less pesticides as compare to fresh food
Reason behind this is following:-
There are number of pesticides application done in field by growers to ensure crop free from pest attach so that we may able to enhance quality and quantity of our crop. But consumer demand for foods which is free or with minimal pesticides residues .So, the grower, food mills and food industry honor processing the food for the purpose to reduce pesticide residues as minimum as possible.
Methods use to remove pesticides residues
These are some following world widely use techniques to reduce pesticide
Washing is very common and cheap method being use in many countries of the world to reduce the pesticides residues from the food. With the help of washing surface residues easily remove but the systemic residues present in tissues will be little affected but the proportion of residue that can be removed by washing decline with time. There are two given method are being used one is hot washing and blanching which is preferably used in commercial washing and second is cold water which use for domestic rinsing. For example washing rice grains with water removed approximately 60% of chlorpyrifos residues. The effectiveness of washing is removing residues depends upon four factors which are:-
- The location of the residue
- The age of the residue
- The water solubility
- The temperature
Residues are usually confined in the outer surfaces which can easily remove with the help of peeling, trimming or hulling operations. These are some fruits likes’ avocado, bananas, citrus, kiwifruits, mango and pineapple in which peeling is best process to achieve virtually complete removal of residues from the fruit. Residues of systemic pesticides can also be enter into the flesh of crop. These are some major peeling methods use to remove toxic substance from fruits, vegetables or other food commodities:-
- Chemical peeling ( mostly sued)
- Mechanical peeling ( mainly abrasion peeling)
- Steam peeling
- Freeze peeling
This is quite common phenomenon which is used by layman in villages’ hulls of cereal grain mostly which contain the majority of pesticide residues from any field treatments.
Again this is very common phenomenon use to for the removal of either inedible parts or parts with defects, or for cutting the raw material to a size that is suitable for further processing. For example pirmiphos methyl residues in rice were reduced 70% and 90% by husking and polishing, respectively. Similarly husking of maize removed 99 % of the residues from field treatments with tetrachlorvinphos.
- Cooking and canning
In this process we use to heat the food commodities at a specific temperature along with water and chemical mixture which help to degrade and volatilize the residues
Pesticide residues depends upon following factors like:-
- Degree of moisture loss
- Whether the system is open or closed
For example only 13% of parathion residues on tomatoes were found in canned juice or ketchup.
- Stir-frying and Canning
Pesticide residues can be effectively decreased by stir-frying. This method can be reduce upto 49 and 53% by peeling and frying.
This method very effective to slow down the senescence process or decay process by decreasing the chemical reaction. Example freezing of tomatoes decreased the pesticide residues from 5 to 26% after six days and 10 to 31 % after 12 days of pesticide contamination.
Drying is very economical and commonly used process for the pesticide residual reduction considerably. For example sunlight drying lead to around 50% decline in bitertanol residues from 0.5 ppm present at harvest. In similar manner by drying process of grapes lead to 64.2-71.9 % losses of methamidophos possibly due to evaporation of the pesticides during the process.
This phenomenon can be scene when we process tea help to reduce 64% pesticides, after this remaining pesticide in tea 36% which later on, when we use it through infusion in water it remains only 16 % in cup. The transfer of quinalphas to the infusion could be due to its solubility in water.
This means precooking of rice within the husk including following things like hydrating paddy, heating to cook the rice and drying of the rice at high temperature(100oC) which help to inactivate or degrade the molecule of pesticides.
To protect our grain loss from storage pest we may applied pesticide in post-harvested commodities because we store our grain for long term (3-36 months) at ambient temperatures in bulk silos. Pesticides can migrate through to the bran and germ. So, the storage and milling help to reduce pesticide residues.
- Chemical solution
Effect of chemical solution on pesticide residues can influence in following ways like:-
- Acidic solutions :-
These are acid solution which are used for the removal of pesticides like citric acid, ascorbic acid, acetic acid and hydrogen peroxide at a concentration of 5 and 10 % for 10 minutes.
- Alkaline solution :-
These are some typical solution like NaOH, acetic acid, potassium dichromate. In this method we dip our fruits in NaOH solution removed 50 to 60% surface residues of pyrethroids compared to 40 to 50% remove by hydrolytic degradation with NaOH and a detergent solution removed 50 to 60% residues omate and soap are used as decontaminating agents.
- Ozonization :-
In this method we use ozone because of its powerful oxidizing property is effectively applied in drinking water and waste water treatment. Tap water and ozone water treatment significantly reduced the pesticide residues on vegetables, as compared to no-wash treatment.
- Neutral solution
In this process we use sodium chloride (NaCl) solution as we increase NaCl concentration pesticide residues automatically reduce. For example 5 and 10 % NaCl solution for 15 minutes rubbed by hand water was decanted organophosphates 100% and organochlorines 28 to 93 %.