|Wednesday, 24 March 2004|
Residues of pesticides in food
by Athauda Jayawardena
Institute of Chemistry, Ceylon, seminar on "Food Safety for the Food Processing Industry"
At present, it is well known that the use of pesticides plays a major role in maintaining food production necessary to sustain the World's population. At the same time, there is very great concern about food safety due to the presence of pesticide residues in food and water all over the world.
It is known that, pesticides are used for the protection of crops from deleterious effects of pests such as insects, fungi, weeds, rodents etc.
The use of pesticides helps minimize potentials crop losses due to adverse effects of pests. In addition, pesticides also play a role in protecting humans from diseases such as Malaria, Filaria, Dengue fever etc by controlling insect vectors that spread these deadly diseases. Protection of farm animals and pets from insect vector borne diseases is another advantage. Preventing of timber, clothes, buildings etc from pest attacks and control of weeds in road-ways and industrial premises are some other uses of pesticides.
This discussions focuses only on the use of pesticides in agriculture in order to fall in line with the topic. There is a great need to feed the ever increasing World's population safely and sustainably.
To achieve this objective, countries both developed and developing have resorted to modern farming practices at varying degree depending on the diversed requirements and affordability. Here the diversed requirements refer to agronomic practices such as, the use of high technology, appropriate technology, drip irrigation methods etc. The magnitude of the challenge can be understood by the projected increases in population as shown below:
In the 1970s, 1.25 hectares have produced food for each person. By the year 2000 only 0.25 hectares was available for producing food for each person.
It has been estimated that total available land all over the world is about 3.6 billion hectares. As it is difficult to increase the extent under cultivation in proportion to the increase in population it is essential to increase production per unit area or the productivity. Preservation of habitat for wild life is one of the major limitations to increasing the extent under cultivation. Increase is productivity can be achieved by the adoption of improved agronomic practices, use of improved high yielding cultivars and by minimizing the crop losses due to adverse effect of pests.
On the other hand, with the advancement in bio-technology the extent under genetically manipulated crops which are resistant to insects, fungi, viruses and herbicides is also increasing at a fast rate. Further, use of Bio-pesticides is also on the increase at present. However, there are no real alternatives on the horizon to herbicides for weed control though there is a belief that genetic manipulation will totally dominate the future.
Weedicides account for about 50% of the crop protection market. Therefore, chemical pesticides will remain a keystone component of crop protection for several decades to come. In view of this, Integrated Pest Management (IPM) is the key to manage pests while safeguarding the user, the consumer and the environment.
Pesticide residues in food
After the second world war there were severe shortages for food almost all over the world. In many countries, rationing of food was a common feature. At that time distinctly primitive pesticide formulations were used in agriculture to meet the increasing demand for food.
However, in 1962 the book titled "Silent Spring" by Rachel Carson highlighted the adverse effects of pesticides on the environment. Later, concern was voiced from some quarters that the potential risks of pesticides outweighed the benefits. Though this view has not diminished it has been tempered in recent years with the realization that food like life is not risk free.
NO EFFECT LEVEL (NEL): The highest dose of a pesticide at which no adverse effects appear in the short or long term in the most sensitive species of animals or equivalent testing methods.
ACCEPTABLE DAILY INTAKE (ADI) - The amount of chemicals which can be consumed every day for the average individual's whole life time with the practical certainty that no harm will result.
The ADI is measured in mg/kg of the body weight but it includes a safety margin of 100 times less than the NEL of that particular pesticides. This assumed that a man is 10 times more sensitive than the most sensitive animal and that the most sensitive man is 10 times more sensitive than the average.
At present, there are regular monitoring programmes in some countries as there is international movement of pesticide residues in food products. Regulations have been enacted in most countries in order to minimize pesticides residue levels in food products to make them safe for consumption. However, monitoring programmes are carried out mostly in developed countries. As a result of this situation, developing countries face problems in exporting their produce to developed countries.
In developing countries more than 50% of available land is cultivated. However, they consume only one fifth of the global amount spent worldwide for pesticides. International trade of agricultural produce is a major increasing factor of pesticide usage mainly due to phytosanitary and plant quarantine requirements. In terms of pesticide group usage developing countries use about 50% of world use of insecticides, 20% of fungicides and 10% of insecticides. However in Sri Lanka the use of herbicides accounts for a little over 40% of the total consumption of pesticides.
This is comparable to the worlds pesticide consumption pattern.
In spite of the national and regional efforts made by the developed countries to update the present registration schemes and food crop tolerances (MRLs) the use of undesirable pesticide groups such as organochlorinated compounds namely DDT, BHC are being used in developing countries like China etc. Economic problems, shortage of more adequate pesticide alternatives and lack of regulatory mechanisms can be attributed to this situation. In Sri Lanka the Regulatory Mechanism is well ahead of many developing countries.
The WHO/FAO Codex Aliementarius Commission deals with methods of analysis and sampling of food products and water. Codex Committee on Pesticide Residues publishers the lists of recommended methods for testing and compliance with the Codex Maximum Residue Limits.
In the UK there is Working Party on Pesticide Residues (WPPR). In the US, in 1996 "The Food Quality Protection Act (FQPA) was enacted. This legislation provides more powers than those of the earlier Food and Drug Administration Act. The FQPA requires an extra 10-fold safety factor to minimize risks to infants and children.
At present, monitoring programmes established by developed countries have detected pesticide residues in a variety of food items such as Legume Crops, Avian Eggs, Rice, Biscuits etc. The high residue levels can be attributed either to higher dose of pesticides used while in production or non adherence to pre-harvest interval or post harvest treatment. According to the findings of a survey conducted during the period 1990 - 1996 the following have been detected as high risk pesticide residues.
The situation in California was significantly lower at 1.6% (CEPA 1995). EU data in 1996 were comparable to those of California.
California adopts a "green approach" to life and may use pesticides more carefully than other states. A similar situation is seen in EU countries as well. This emphasizes the importance of prudent use pesticides.
According to data collected, most pesticide residue detection were below established tolerance levels. Further, many were below the 50% tolerances.
In view of the above, it is important to keep risks in perspective. The following will show that many of life's daily risks are significantly greater than the risk of pesticide residues.
Potential risks and benefit of eating fruits and vegetables treated with pesticides Based on data collected from developed countries the residues detected have been extremely small and several folds lower than the ADI. However, in developing countries, it is essential to ensure that pesticides are prudently used.
Harmonization of registration requirements and establishment of uniform sets of MRLs are vital to streamline the international trade of food items. The following explains the necessity for a Harmonized procedure.
* A pesticide legally registered in a country may not have been registered in the importing country. The presence of residues of this pesticide becomes a trade barrier for the exporting country.
* The residue level exceeds the tolerance established in the importing country though the residue level complies with the MRL set by the Codex Alimentarine Commission. Some countries, especially in the EU have established their own tolerances, which are lower than the MRLs established by the Codex Alimintariues Commission. This becomes a constraint to exporting of products, which fall in line with Codex MRLs.
* Enactment of the Food Quality Protection Act in the US. It requires extra 10% safety margin. The other countries rely on the accepted 100-fold safety margin adopted by the pesticide inventing companies in their product development process. The countries which use pesticides manufactured by companies which have not followed the FQPA may face problems in exporting their produce to the US.
* Lack of evaluation facilities in most of the developing countries. Multiple residue analytical facilities should be available as several pesticides of the same group can be used in a crop. Further, if several pesticides of the same group are used in a country multi residue analytical facilities should be available to detect residues in water.
For example according to the European drinking water Directive (80/778/CE) of 997 states that individual pesticides concentration and the sum of all individual pesticides in water should not exceed 0.1 and 0.5 micro g/L respectively.
It should be noted that the risk associated with pesticides residues has been over exaggerated. Further the pesticide industry now develops pesticides which are of very low mammalian toxicity with less persistence in the environment. The required amount per unit area is also comparatively very low.
That means new pesticides are less toxic and more environment friendly. In order to preserve natural balance new products are specific in activity and therefore they control only the targeted pests without affecting the other organisms including beneficial ones.
However, appropriate mechanisms such as establishment of regular residue monitoring programmes, increasing the frequency of awareness programmes for users of pesticides and consumers, formulation of regulations and devising methods to minimize residue levels etc should be employed in developing countries like ours to ensure that the residues of pesticides in foods are at acceptable levels.
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