Dr. Sudhanya Nath
PhD Scholar, Department of Animal Nutrition, West Bengal University of Animal & Fishery Sciences, Kolkata, West Bengal – 700037, India
Email: sudhanyanath@yahoo.com
INTRODUCTION
Use of pesticides in India began in 1948 when DDT was imported for malaria control and BHC for locust control. Since then various synthetic pesticides are used for protection of crops and public health. The persistence nature of some of these pesticides led to their accumulation in animal tissues and subsequently causes human dietary exposure to these pesticides through consumption of animal products viz. meat, milk, eggs and sea-foods. Scientific evidence suggest that even such low dose but long term exposure can cause serious health hazards to human health and environment as well. The positive side of the use of pesticides include enhancement of economic potential in terms of increased production of food and fiber as well as prevention of vector-borne diseases, whereas on the negative front this resulted in serious health implications to man and his environment in the form of variety of known and unknown toxic symptoms. The pesticides and insecticides used in the storing process of feed in the godowns can affect the livestock and mankind. So, the pesticides and insecticides should be used in a controlled way following the strategies to have minimal residual effect on the consumers.
CAUSES OF INFESTATIONS :
Insect pests in stored grain need certain living conditions to feed, reproduce and survive. In some cases we might have unwittingly provided an ideal living environment for insects even before grain is stored. The following measures are effective and simple ways of preventing pest development:
• Thoroughly cleaning the inside of the bin
• Removing spills or grain lying outside of bins
• Cleaning and treating structures before filling them. This is especially important prior to harvest.
• Maintaining Grain bins will protect grain and maintain its optimum quality.
• Weather-proofing grain bins helps keep out insects. It also seals grain bins from moisture that can lead to spoiling and a reduction in grain quality.
• Weed management around bins is as important as controlling weeds in the field. Weeds or volunteer cereal grains around bins attract insect pests. Various weed seeds discovered in a grain shipment can result in a prohibition of export.
• Keeping areas around grain bins clean helps prevent insect infestations in stored grain.
TYPES OF INSECT PESTS :
Insect pests in stored grain are considered either primary or secondary.
• Primary insect pests have the ability to infest, feed and reproduce on whole, sound grain.
• Secondary insect pests require mould or damaged grain kernels infested by primary insect pests to survive.
Many stored product insect pests are strong fliers. They can migrate distances that are greater than just a few metres. When grain is warm, it emits odours that attract insect pests from great distances. When stored grain is properly maintained, there is less chance of mould growth and insect infestations and subsequent damage to grain quality.
INSECTICIDES USED FOR STORAGE STRUCTURES :
There are several insecticides available for treating cracks and crevices in buildings or empty bins and other storage containers :
• Malathion
• Pyrethrins
• Cyfluthrin
• Diatomaceous earth
INSECTICIDES FOR DIRECT APPLICATION TO GRAIN :
DIATOMACEOUS EARTH
• Absorbs waxy layer on insect skin causing death by desiccation of insect.
• Most effective when applied as dry grain is augured into a bin during harvest.
• Treatment for a 6-week period at above 20°C is necessary to ensure maximum efficacy.
• Diatomaceous earth has the potential to reduce test weight. Lower auger flow rates when applying as diatomaceous earth increases grain friction.
MALATHION
• Incapacitates the insect’s central nervous system.
• Best applied as a liquid spray or dust as grain flows through an auger or conveyer.
• Intended for use on cereal grains. It is not registered for use on oilseeds.
• Ensure that the formulation used is registered for direct grain treatment.
• Grain treated with malathion should not be sold for 7 days.
ALUMINUM PHOSPHIDE (PHOSPHINE)
• It is applied as pellets to bulk grain either as the grain is entering storage; or placed into the grain with a probe after the grain is stored; or contained in pre-packaged devices (ropes) on grain surface.
• Structures must be well sealed for effective treatment.
• Aluminum phosphide reacts with water in the air to produce the gas phosphine.
• Grain temperature and moisture are both factors in contributing to the effectiveness of aluminum phosphide. Grain should not be fumigated if the temperature is less than 5°C or if the moisture content is less than 10%.
• Eggs are the most resistant stage, requiring approximately 20 times higher doses to control than adults and larvae.
• Phosphine used according to the label will control all life stages and all stored-grain insect pests.
• Monitoring of phosphine during fumigation will ensure that gas levels are sufficient to control insects.
• Phosphine may cause corrosion of certain metals (copper, brass, silver and gold) at high temperatures and humidity. Precautions should be taken to remove or protect equipment containing these metals such as electrical motors, wiring and electronic systems.
• Insect resistance to phosphine is known to occur in the US and Australia and continuous or inappropriate use may result in resistance developing.
MAGNESIUM PHOSPHIDE (PHOSPHINE)
• Like aluminum phosphide, magnesium phosphide reacts with water in the air to produce the gas phosphine.
• Magnesium phosphide generates phosphine faster that aluminum phosphide.
• Unlike aluminum phosphide, magnesium phosphide cannot come in contact with the commodities fumigated.
• Magnesium phosphide is applied contained in plates, pouches or strips.
• Mainly used for fumigating empty structures or tarped commodities.
• Similar issues with temperature, humidity and corrosion of metals as aluminum phosphide.
• Structures must be well-sealed in order for treatment to be effective.
GASEOUS PHOSPHINE
• Gaseous phosphine (compressed gas in a cylinder) allows a more precise dosage of phosphine and faster fumigation than the metal phosphides.
• Fumigation at minimum temperature of 0°C, compared to metal phosphides with a minimum temperature of 5°C.
• Similar issues with corrosion of metals as aluminum phosphide.
• 2 formulations:
o ECO2FUME® (ready for application),
o VAPORPH3OS® (needs onsite dilution).
CARBON DIOXIDE
• Carbon dioxide is applied to grain as a gas from cylinders.
• Structures must be well sealed for effective treatment.
• Dose: Maintain at 60% for 4 days between 20°C and 25°C.
METHYL BROMIDE
• Methyl bromide can be used for quarantine and pre-shipment applications either for export or for import.
• The only quarantine insect for stored grain is the khapra beetle (Trogoderma granarium).There are several other non-grain pests that are found on wood or other commodities that may need to be fumigated before export or import.
• In the past, methyl bromide was used to fumigate flour mills and structures and grain to control stored grain insect pests, but this use has been almost entirely stopped because of restrictions under the Montreal Protocol on Substances that Deplete the Ozone Layer.
FUMIGATION :
Several factors are important in assuring successful fumigation:
• Grain should always be level in the bin to let the fumigant penetrate evenly.
• Any surface caking or crusting should be broken up and removed.
• Grain temperature should be 60°F or higher to ensure proper vaporization.
• Possible leak points such as cracks or holes in the bin should be closed
before fumigation since leakage may result in under treatment and poor
control.
CAUSES OF FUMIGATION FAILURES :
Fumigation failures can usually be attributed to the following:
• INSUFFICIENT FUMIGANT–A fumigant’s efficiency depends on its attaining a lethal concentration in the grain. Results will not be satisfactory if less than the recommended dosage is used or if the fumigant is applied under unfavourable conditions.
• STORAGE STRUCTURE–Leaky bins will not retain fumigants long enough to kill the insects. The depth of grain also affects a fumigation’s efficiency. In general, the greater the surface area of the grain in relation to bulk, the greater the difficulties in adequate fumigation. As a result, flat storage bins require higher dosages than do round silo bins. Also, storage structures with a large amount of space over the grain are difficult to fumigate effectively because large amounts of gas escape into that space.
• MOISTURE–As moisture content increases above 12% a proportionately higher dosage of fumigant is required. It is difficult to effectively fumigate grain having a surface moisture content of 15 to 20% because the fumigant vapours will not penetrate the moist layer.
• TEMPERATURE–During fumigation, the gas quickly assumes the temperature of the grain. Fumigant activity increases as temperature increases. However, if grain temperature reaches or exceeds 115 °F, the fumigant may vaporize very rapidly and escape from the bin before accomplishing the job. On the lower end of the spectrum, stored grain insects are inactive at temperatures below 60°F. Fumigation should be delayed until the grain temperature increases.
PFA Maximum Residue Limits for pesticide residues in meat and poultry:
SL. NO Name of insecticide Tolerance (ppm or mg/kg)
1 Aldrin, dieldrin 0.20
2. DDT 7.00
3. Fenitrothion 0.03
4. Lindane 2.00
5. Chlorfenvinphos 0.20
6. 2,4-Dichlorophenoxyacetic acid (2,4D) 0.05
7. Chlorpyriphos 0.10
8. Monocrotophos 0.02
9. Ethion 0.20
10. Trichlorfon 0.10
11. Carbendazim 0.10
12. Benomyl 0.10
13. Carbofuran 0.10
14. Cypermethrin 0.20
15. Edifenphos 0.02
16. Fenthion 2.00
17. Fenvelerate 1.00
18. Phenthoate 0.05
19. Pirimiphos-methyl 0.05
PREVENTION AND CONTROL OF RESIDUES IN FOOD :
The Government of India has taken steps to ensure the safe use of pesticides. The Insecticide Act, promulgated in 1968 and enforced on 1st August, 1971 envisages to regulate the import, manufacture, sale, transport, distribution, and use of insecticides, with a view to prevent risks to human beings or animals, and for matters connected therewith. In India, work on monitoring of pesticide residues in various food commodities viz. fruits, vegetables, meat, eggs and seafoods has been recently initiated at National level by Indian council of Agricultural Research, New Delhi through their centres located in different parts of the country.
EFFECT OF PESTICIDES ON POULTRY :
Chlorpyrifos as an organophosphate, is one of the most widely used insecticides in agriculture worldwide to control wide range of insect and arthropod pests in agriculture. Chlorpyrifos is also applied to the soil surrounding or beneath buildings as protection against termites including chicken. The indiscriminate use of insecticides has led to a widespread concern over the potential adverse effects of these chemicals on human and animal health. The exposure to low levels of chlorpyrifos over a long period of time would have more serious impacts on human and animal health.
Chronic toxicity of chlorpyrifos to birds has adverse effects on fertility, hatchability and embryo deformities including twisted necks and shortened/indented backs in bobwhites and adult chickens and reduction in body weight, egg production, eggshell thickness, egg weight and hatchling weight. Significant decline in the humoral immunity was also reported in broilers due to chlorpyrifos chronic toxicity and supplementation of vitamin C has significantly enhanced the immune response. Vitamin C protects cells from oxidative stress by scavenging free radicals.
CONCLUSIONS
Public concerns about the adverse environmental and human health impacts of pesticide residues led to strict regulations on their use in India two decades ago. Nevertheless, DDT and several other organochlorine pesticides are still being used for agriculture and public health programmes in India. As a consequence Indian consumers are exposed to greater dietary levels of these pesticides. Therefore, the design and implementation of appropriate epidemiological studies and their integration with monitoring of samples from foods of animal origin as well as environmental samples would be a major step in assessing the risk of pesticide residues in meat and controlling or eliminating them. With the continued globalization of trade in food products and the concomitant risk that the food contamination through point-source pollution may be widely distributed, identification of sources and their control should be matters of international concern, research and action.
To sum up, based on our limited knowledge with indirect and/or inferential information, the domain of pesticides and insecticides illustrates certain ambiguity of a situation in which people are undergoing life-long exposure. Therefore, there is every reason to develop health education packages based on knowledge aptitude and practices and to disseminate it within the community for minimizing human exposure to pesticides and insecticides.
