• In Latin America, 10 to 30 per cent of agricultural workers show inhibition of the blood enzyme, cholinesterase, which is a sign of organophosphate poisoning.
• In Venezuela, 10,300 cases of poisoning with 576 deaths occurred between 1980 and 1990.
• In Brazil, 28 per cent of farmers in Santa Catarina state say they have been poisoned at least once and in Parana state some 7,800 people were poisoned between 1982 and 1992.
• In Egypt, more than 50 per cent of cotton workers in the 1990s suffered symptoms of chronic pesticide poisoning, including neurological and vision disorders.
• In China, 42,800 new cases of pesticide poisoning were reported in 1994, including 3,900 fatalities. Many were said to be victims of homemade cocktails marketed illegally.
Aquaculture is a new and rapidly growing industry and it has created a new concern in pesticide use. Sea lice often attack farmed salmon, causing scarring, infection and, sometimes, death. To eliminate them, the salmon are confined by a closely drawn net and surrounded by a tarpaulin. Dichlorvos, which is the active ingredient in the familiar household pesticide strips, is then added directly to the water. At present, the environmental effects of this pesticide are unknown. The pesticide is toxic to lobster larvae, however, and it may have other undesirable properties.
Pesticides can adversely affect wildlife through changes in the food web, direct and indirect poisoning, chemical "bioconcentration", and habitat changes. And their harmful effects may show up in animals, which have no direct relationship to the original pest. In the 1960s, wildlife biologists were puzzled when the gannet population on Bonaventure Island, Quebec, began to shrink. The shells of the gannets' eggs were too thin to protect the embryos. Only after the eggs had been analysed did the scientists identify the culprit DDT, which had been bioconcentrated through higher levels of the food web. Populations of other predatory birds such as ospreys, eagles and peregrine falcons also declined when the birds accumulated DDT through their food.
Many of the birds that nest in Atlantic Canada are migratory. Some spend a large part of the year in Central and South America, where pesticide application may be more intensive and may include organochlorines, which are banned in Canada. Such birds are thus subjected to a "double whammy" exposure to toxic pesticides at both ends of their migration paths.
Modern chemical pesticides are much less persistent, but they may be highly toxic to some non-target organisms. Phosphamidon, for example, which was intended to replace DDT in forest protection, killed large numbers of birds. The spraying of fenitrothion, which replaced both DDT and phosphamidon, has less severe effects, but it still remains a cause for environmental concern.
Pesticides also change wildlife habitat. If a herbicide kills hardwood cover, birds and mammals, which depend on that habitat, cannot live there any longer. Nor can their predators. There are both winners and losers, however, since other animals may benefit from the changes. Either way, the habitat changes caused by the herbicide ripple out through the entire biological community.
Pesticides enter watercourses primarily through direct application, aerial spray drift and run-off from treated areas. Rinsing and filling spray equipment near streams is also a problem, which can result in widespread contamination, killing fish and aquatic insects. Many pesticides enter aquatic sediments where they can persist for long periods of time. Populations of aquatic insects, an important food source for fish, have been drastically reduced after forest and agricultural spraying. Under some conditions, the spraying of insecticides such as deltamethrin and endosulfan may result directly in the death of fish. When herbicides enter watercourses they may also affect vital plant life in aquatic systems.
Groundwater moves slowly, and once groundwater supplies are contaminated they may remain so for decades. Scientists are particularly concerned about heavily farmed areas in the Atlantic Provinces, where agriculture makes extensive use of pesticides. A number of pesticides such as aldicarb, carbofuran and phorate have been detected in local wells.
Many pesticides are now suspected endocrine disruptors.Hormones get their name from the Greek word meaning 'to urge on'. They are chemical messengers produced and released into the bloodstream by organs known as the endocrine glands. These include the testicles, the ovaries, the pancreas, the adrenal glands, the thyroid, the parathyroid and the thymus. These play a crucial role in helping the foetus to grow in the womb, in the development of the baby and young child, and in the sexual development of both male and female. Endocrine-disrupting chemicals interfere with these hormones, most crucially at the stage when the baby is developing in the womb. But they can also mimic the hormone or block or stimulate its action in adults. So, for example, the pesticide endosulfan affects the body's oestrogen. Amitrole can affect levels of hormones in the thyroid gland and a number of organophosphate and carbonate pesticides have been linked to lower sperm counts. The direct effects of people using some of these chemicals are terrible. It is particularly bad for farm workers in the Third World who don't have the protective clothing or the ability to protect themselves.
Chemical pesticides are effective and powerful. Farmers and foresters will no doubt continue to use them. All the same, society's growing concern about environmental risks makes alternative methods of pest control increasingly attractive.
An alternative method to chemical pest control is using biological pesticides or Biopesticides. Biopesticides are certain types of pesticides derived from such natural materials as animals, plants, bacteria, and certain minerals. For example, canola oil and baking soda have pesticidal applications and are considered biopesticides. At the end of 1998, there were approximately 175 registered biopesticide active ingredients and 700 products. Biopesticides fall into three major classes:
Microbial pesticides consist of a microorganism (e.g., a bacterium, fungus, virus or protozoan) as the active ingredient. Microbial pesticides can control many different kinds of pests, although each separate active ingredient is relatively specific for its target pest/s. For example, there are fungi that control certain weeds, and other fungi that kill specific insects. The most widely used microbial pesticides are subspecies and strains of Bacillus thuringiensis, or Bt. Each strain of this bacterium produces a different mix of proteins, and specifically kills one or a few related species of insect larvae. While some Bt's control moth larvae found on plants, other Bt's are specific for larvae of flies and mosquitoes. The target insect species are determined by whether the particular Bt produces a protein that can bind to a larval gut receptor, thereby causing the insect larvae to starve. Examples of different Bacteria approved by the Office of Pesticide Programs as pesticide active ingredients include: Bacillus cereus Strain, Bacillus sphaericus Serotype H5a5b strain, Bacillus subtilis, and Bacillus thuringiensis subsp. Israelensis. For example Bacillus subtilis GBO3 is a bacterium that is used as a fungicide on flower and ornamental seeds, and on agricultural seeds including seeds for cotton, vegetables, peanuts, and soybeans. The bacterium colonizes the developing root system of the plant and thus competes with certain fungal disease organisms. It isintended to aid in the suppression of plant diseases caused by such fungi as Rhizoctonia, Fusarium, Alternaria, Aspergillus and others that attack the root systems of plants. Examples of different Fungi approved by the Office of Pesticide Programs as pesticide active ingredients include: Ampelomyces quisqualis, Beauveria bassiana, Candida oleophila, and Colletotrichum gloeosporioides. aeschynomene. For example Beauveria bassiana strain GHA is a fungus that is used as a pesticide for controlling many kinds of insects. The active ingredient can be used on all food crops and many non-food crops at various outdoor and indoor sites. Residues of the pesticide are not expected to remain on treated food or feed.
Plant-pesticides are pesticidal substances that plants produce from genetic material that has been added to the plant. For example, scientists can take the gene for the Bt pesticidal protein, and introduce the gene into the plants own genetic material. Then the plant, instead of the Bt bacterium, manufactures the substance that destroys the pest.
Biochemical pesticidesare naturally occurring substances that control pests by non-toxic mechanisms. Conventional pesticides, by contrast, are generally synthetic materials that directly kill or inactivate the pest. Many plants and animals produce chemicals that can be used as natural pesticides. For example, the chemical that makes these chilli peppers taste hot also repels pests like aphids, ants and flies. Home gardeners often use oils from lemon, lime and orange peels. These oils keep pests like caterpillars, aphids and flies from attacking valuable plants. Biochemical pesticides include substances, such as insect sex pheromones. Pheromones are chemicals that insects produce to communicate with each other. Fruit growers often use pheromones to control the reproduction of codling moths. Special devices release female codling moth pheromone into the air. The extra pheromone confuses the male moth and prevents him from finding his mate.
Farmers depend on a method called "crop rotation" to control pests. A variety of crops are planted and then rotated to different fields each year. Pests that attack one variety will die off when that variety is replaced by a different crop the following year. In many cases, removing their preferred food and shelter can control pest populations. Covering food that attracts flies, or removing garbage that attracts animal pests, is often all that is required.
Integrated Pest Managementtreats a crop as an ecosystem, and uses different methods to control the pests within it. The guiding principle of integrated pest management is that active pest control is only undertaken when pest populations are at, or near, "economic thresholds" which may threaten a crop's commercial value.
Integrated pest management uses biological controls wherever possible, but it also uses other techniques if necessary including limited, specific applications of a chemical pesticide. The integrated approach actually tolerates some pests, so long as the damage they cause remains minor. In fact, small pest populations are welcome, since they ensure that the pest's natural enemies will also survive in the system.
Integrated pest management is not always easy, or even possible. Climatic conditions, an absence of natural enemies, or the biological complexities of the crop itself may prevent a focused attack on one pest only. The technique requires time, knowledge and dedication on the part of the farmermanager.
Natural pesticidal products, also called botanical pesticides, are available as alternatives to synthetic chemical formulations. Although thought of by some as "natural," and therefore assumed to be harmless, safety clothing must be worn when spraying these, even though their toxicity is low to warm-blooded animals. Some botanical pesticides are toxic to fish and other cold-blooded creatures and should be treated with care.
The botanical insecticides break down readily in soil and are not stored in plant or animal tissue. Often their effects are not as long lasting as those of synthetic pesticides. For example, Pyrethrum works against Pickleworms, aphids, leafhoppers, spider mites, harlequin bugs, cabbageworms, Mexican bean beetles, flea beetles, flies, and squash bugs.
Advantages of using biopesticides include: Biopesticides are usually inherently less harmful than conventional pesticides. They generally affect only the target pest and closely related organisms, in contrast to broad spectrum, conventional pesticides that may affect organisms as different as birds, insects, and mammals. Biopesticides often are effective in very small quantities and often decompose quickly, thereby resulting in lower exposures and largely avoiding the pollution problems caused by conventional pesticides. When used as a component of Integrated Pest Management (IPM) programs, biopesticides can greatly decrease the use of conventional pesticides, while crop yields remain high.
The world's five main pesticide producing and exporting states are France, Germany, the US, Britain and Switzerland although the fastest-growing markets are in Brazil, Germany, Spain, France, the Netherlands, Australia and Canada. Many of the same countries also import pesticides: imports grew from a world total of $8.0 billion in 1991 to $11.6 billion in 1998.
References
USING THE SEARCH ENGINE: THESE SITES WERE FOUND:
1) Writing DEN: Alternatives to Chemical Pesticides
www.actden.com/writ_den/e03/direct.htm
2) NASD Database: Documents by Topic: Chemicals/Pesticides
www.cdc.gov/niosh/nasd/menus/topchem2.html
3) Alternates to Chemical Pesticides
www.ns.ec.gc.ca/epb/fiddle/alternat.html
4) Biological pesticides from Ecogen Inc.
www.ecogeninc.com
5) http://www.oneworld.org/ni/issue323/contents.htm
6) www.epa.gov/pesticides/biopesticides/factsheets/recentfactsheets.htm
7) http://www.epa.gov/pesticides/biopesticides/
8) search biological pesticides
9) Compton's Interactive Encyclopaedia 1999(CD-ROM)- biological pesticides
10) Class notes from OCR examination board on pesticides
11) AS Biology, specification (A), Module 2: Making use of biology
Published by Collins, Student support material for AQA
By Mike Boyle, Series consultant: Bill Indge
Page 35
12) Pesticides and your food- How to reduce the risks to your health
By: Andrew Watterson
First published in 1991 by Green Print
Part 1- Pesticides and why they are used
Page 1-7