FOOD TOXOCOLOGY

1. P O S T G R A D U A T E F O R Z O O N O S E S A N D F O O D
S A F E T Y
2 6 - 0 3 - 2 0 1 9
Pesticide Residue In Food Supply.
Presented by Abubakar M. Adam.
Mekelle university

2. WHAT ARE PESTICIDES?
 The term “pesticide” indicates any substance or mixture
of substances used to kill, repel, or otherwise control a
“pest”, including insects, snails, rodents, fungi, bacteria
and weeds.
 Pesticide Classification
Pesticides can be grouped in a number of different
ways. Most commonly, they are grouped according to:
1. Their target (the pests they control)
2. Their mode of action (the way they control the pest)
3. Their chemical structure.
4. Their method of application.
5. The timing of their application.

3. PESTICIDE USING PURPOSES
 Pesticides may be used in a variety of different ways
during the production of food:
Used by farmers to control the growth of weeds, or
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.

4. What is pesticide residues ?
 Defined by the World health organization (WHO) as,
"Any substance or mixture of substances in food for
man or animals resulting from the use of a pesticide
and includes any specified derivatives, such as
degradation and conversion products, metabolites,
reaction products, and impurities that are considered
to be of toxicological significance."
Processed foods have less Pesticides than fresh foods
 Growers : don’t need to ensure that their foods are
cosmetically perfect.
 Processors : consumer demand for foods with minimal
pesticide residues.
 Processing : reduce pesticide residues.

5. Residues can arise from:
1. The use on a crop of legally allowed pesticides
according to good agricultural practice – (leave
smallest and acceptable amount of residue).
2. Overuse of a pesticide, or use too close to harvest, of a
legally permitted pesticide.
3. Illegal use of a pesticide that is not approved for that
Crop.
4. Incorrect use of pesticides after harvest, to reduce pest
infestation in storage or in transit.

6. Pesticide residue may be present in:
Fresh or tinned fruit and vegetables.
Processed food and drink made from the crop (e.g.
juice, bread or any other manufactured food or drink).
Fresh or processed animal products (if the animals have
been fed on crop treated with pesticide).
 Occasionally, residues may also result from
environmental or other ‘indirect’ sources
(e.g.residues of old pesticides, such as DDT).

7. Pesticide Tolerance
 Amount of pesticide residue allowed by regulatory
agencies to remain in or on a harvested crop.
 Ability of a mutated pest to survive the harmful effects
of a previously effective pesticide.

8. METHODS USE TO REMOVE PESTICIDE
RESIDUES
Washing
Peeling
Hulling
Trimming
Cooking + Stir-
frying
Canning
Freezing
Drying
Infusion
Parboiling
Storage
Chemical
solution
Neutral solutions

9. Washing
Washing
 Surface residues -simple washing operations
 Systemic residues -present in tissues will be little
affected.
 The proportion of residue that can be removed by
washing declines with time.
 Hot washing and blanching- cold washing.
 Commercial washing- Domestic rinsing

10. The effectiveness of washing in removing
residues depends upon four factors.
1. The location of the residue.
2. The age of the residue.
3. The water solubility .
4. The temperature.

11. Peeling
 Residues are confined to the outer surfaces removal in
peeling, hulling or trimming operations.
 Peeling fresh fruits such achieves virtually complete
removal of residues from the fruit.
Avocado
Bananas
Citrus
Kiwifruit
Mango
Pineapple

12. Peeling methods:
Peeling methods:
 Chemical peeling (mostly lye peeling)
 Mechanical peeling (mainly abrasion peeling),
 Steam peeling
 Freeze peeling
Residues of systemic pesticides can enter the flesh of
crop!

13. Hulling and Trimming
Hulling
 The hulls of cereal grains generally contain the
majority of pesticide residues from any field
treatments
Trimming
 Removal of either inedible parts or parts with
defects, or for cutting the raw material to a size that
is suitable for further processing.

14. Cooking and canning
Pesticide residues depend on:
 Time.
 Temperature.
 Degree of moisture loss.
 Whether the system is open or closed.
 When the heat increases degradation and volatilization of
residues increases.

15. Stir-frying
Pesticide residues can be effectively decreased by stir-
frying.
 These can be reduced up to 49% and 53% by peeling
and frying .

16. Freezing
Freezing :
slows food decay.
slow most chemical reactions.
 Example
Freezing of tomatoes decreased the pesticide residues
from 5 to 26% after 6 days and 10 to 31% after 12 days
of pesticide contamination.

17. Drying
Drying has been found to reduce the pesticide residues
considerably.
 Example
 Sunlight drying lead to around 50% decline ibitertanol
residues from 0.50 ppm present at harvest.
 Drying of grapes lead to 64.2–71.9% losses of
methamidophos possibly due to evaporation of the
pesticide during the process.

18. Infusion and Parboiling
 Tea: 64% processing…….. 36%remain........... 16%of
the pesticide is transferred to cup-infusion
 The transfer of quinalphos to the infusion could be due
to its solubility in water.
 Parboiling
 Means precooking of rice within the husk.
 Parboiling : hydrating padd + heating to cook the rice +
drying of the rice.
 High temperature (100 C)…. inactivation or degradation
of pesticides.

19. Storage
Grains stored
 Long term (3–36 months)
 At ambient temperatures
 In bulk silos
Insecticides may be applied post-harvest to reduce
losses from storage pests.
 Pesticides can migrate through to the bran and germ.
Storage + milling =Reduced pesticide residues

20. EFFECT OF CHEMICAL SOLUTIONS ON PESTICIDE
RESIDUES
1. Acidic solutions
 Citric acid
 Acidic solution
 ascorbic acid
 Acetic acid
 Hydrogen peroxide
 At a concentration of 5 and 10% for 10 minutes
reduction of pesticide residues.
 Acidic solutions neutral and alkaline solutions.

21. 2. Alkaline solution
 Solutions of NaOH, acetic acid, potassium
dichromate.
 Dipping of fruits in NaOH solution removed
50% to 60% surface residues of pyrethroids
compared to 40 to 50% removal by hydrolytic
degradation with NaOH and a detergent solution
removed 50 to 60% residues omate and soap are
used a decontaminating agents.

22. Ozonation
 Ozone because of its powerful oxidizing
property is effectively applied in drinking
water and waste water treatment
 Tap water treatment + ozonated water
treatments significantly reduced the
pesticide residues on vegetables, as
compared to no-wash treatment.

23. 3. Neutral solutions
Sodium chloride (NaCl) solution
 5 and 10 % NaCl solution for 15 minutes rubbed by
hand water was decanted ----28 to 93% organochlorines
100 % organophoshates.
NaCl concentration increases pesticide residue
decreases.

24. You can do this!
 Grow some of your food using organic methods.
 Buy organic food.
 Wash and scrub all fresh fruits, vegetables
 Eat less or no meat.
 Trim the fat from meat.