Pesticides. There are many reasons why pesticides are used, interspecific competition (competition between members of different species for resources)
Pesticides
Pesticide - Any substance used to kill, repel or otherwise control a pest. These include insecticides, herbicides, fungicides, rodenticides and disinfectants. Pesticides are designed to be toxic and can pose a risk to children, adults, pets and other creatures and plants. Common pesticides include herbicides for weed control, indoor ant and roach sprays, outdoor foggers, insect repellents, flea collars and pet shampoos.
Synthetic fertilizers and pesticides have played a dominant role in agricultural intensification in industrialised and developing countries for decades. Although both have become widely distributed in the environment, most of the concern related to the health consequences of agriculture now centres on pesticides. 7
There are many reasons why pesticides are used, interspecific competition (competition between members of different species for resources) between weeds and crops as well as insects can cause much economic damage to a community, by causing crops to be lost, property damage from termites and tree roots and also damage caused to clothes from moths. However not only economical damage is caused by pests, also medical damage as Bubonic plague is passed on by fleas on rats, Lyme disease by ticks on deer and other animals and also Encephalitis transmitted by mosquitoes. Which is why pesticides are used in more than 69 million households out of 94 million total households in the U.S 3
The graph above demonstrates how the use of pesticides is becoming more common in developing countries because of their properties to rid the area of native insects, which would normally dominate fields destroying crops.
The most popular insecticides in the developing world are often older, broad-spectrum compounds belonging to the organophosphate and carbonate classes chemical families noted for their acute toxicity. These products are popular partly because they are no longer under patent protection and thus are considerably cheaper than the newer, still-proprietary pesticides increasingly used in more developed countries.6 There are also methods of using biological agents as pesticides, for instance an insect may be introduced that feeds primary on a target plant that is competing with a crop. The result being that the insect feeds on the weed and frees ...
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The most popular insecticides in the developing world are often older, broad-spectrum compounds belonging to the organophosphate and carbonate classes chemical families noted for their acute toxicity. These products are popular partly because they are no longer under patent protection and thus are considerably cheaper than the newer, still-proprietary pesticides increasingly used in more developed countries.6 There are also methods of using biological agents as pesticides, for instance an insect may be introduced that feeds primary on a target plant that is competing with a crop. The result being that the insect feeds on the weed and frees up resources for the crop. A similar tactic is introducing an organism that hunts an organism that feeds on a crop. However introducing an organism to a community can have unforeseen consequences for example "the English sparrow, which was introduced onto Long Island for the purpose of controlling insects on grain which as a result has nearly caused the extinction of bluebirds and other songbird species" 8
Properties of Pesticides
The properties of pesticides determine their fate and behaviour in the environment. These properties include their persistence (its ability to remain unchanged), volatility (is its ability to evaporate) and solubility in water (which means they may adversely affect fish and other organisms.)
When pesticides are released into the environment, they are either: 1) broken down, or degraded, by the action of sunlight, water or other chemicals, or micro organisms, such as bacteria; or 2) resist degradation and thus remain unchanged in the environment for long periods of time.5
Properties of the Environment
The individual properties of soil, water and living organisms affect the fate and behaviour of pesticides. Climate and topography also play a role. Soils vary in their ratios of sand, organic matter, metal content, acidity, porosity, permeability, etc. These soil characteristics influence the behaviour of pesticides. Water characteristics also vary and influence pesticide behaviour. Some of the characteristics are acidity, depth, temperature, clarity, flow rate, presence of biological organisms and general chemistry.
Living organisms accumulate certain pesticides. Through the process of bioaccumulation, pesticides accumulate in lower organisms and are passed to higher organisms in the food chain when eaten. The higher organism will accumulate the pesticides at higher levels than their food source. Pesticide levels in fish, for example, can be tens to hundreds of thousands of times greater than ambient water levels in which they live.
Humans are at the top of the food chain. They bioaccumulate the pesticides accumulated by the lower animals and plants that they eat. It is not only fish but also domestic farm animals and plant food, which can accumulate pesticides. Care must be used in the use of pesticides in agricultural as well as home and garden scenarios. To minimise the amount of pesticides humans consume. 5,6
Health concerns of pesticides
Pesticides are designed to kill living organisms and to give an example studies on animals have shown that of the 34 chemicals encompassing 95% of lawn pesticides, 10 are carcinogens, 12 caused birth defects, 20 are neurotoxic, seven alter the reproductive process, 13 cause liver and kidney damage and 29 are irritants.
DEET, the active ingredient in many insect repellents, is responsible for more than 5,000 poisonings every year in the U.S. (Statistics published by National Capitol Poison Centre, Georgetown University Hospital, Washington, D.C.) DEET can cause central nervous system disturbances, dermatitis, and skin irritation.
Inactive or inert ingredients are another problem with pesticides. Inert ingredients are designed to preserve the active ingredients, make them easier to apply or improve their killing ability. Information on inert ingredients is not required to be put on a product's label because this information is considered proprietary. These ingredients typically comprise between 80 - 90% of a pesticide, and in some cases are more toxic than the active ingredients.
Children and individuals with impaired immune systems are more vulnerable to pesticide poisoning. Children have higher metabolic rates, and absorb higher concentrations of toxins from the environment than adults. In addition, children have not fully developed their body's defence systems against toxins. Their livers and kidneys, the organs that detoxify and excrete foreign substances, and act as barriers to absorption of toxic substances, have not fully developed.
Exposure to pesticides can lead to an array of acute effects, depending on the pesticide's toxicity and the dose absorbed by the body. For pesticides with high acute toxicity, exposure can produce symptoms within minutes or hours, most of which diminish in time. These acute effects known as poisonings or intoxications run from mild headaches and flu-like symptoms, to skin rashes, to blurred vision, and other neurological disorders.
The acute effects of pesticide exposure are relatively well understood, whereas much more uncertainty surrounds long-term or chronic effects, especially those believed to arise from low-level exposures to pesticide residues in food or water. There is little dispute regarding the nature of some chronic effects, such as those that follow high-dose exposures. Several studies have shown that many people who experience acute pesticide poisoning from organophosphates later suffer neurological damage. Symptoms of this problem include weakness, tingling, or even paralysis in the legs due to dieback of some nerve endings, and reduced memory and attentiveness.3,5,6
Bibliography
. Statistics published by National Capitol Poison Centre, Georgetown University Hospital, Washington, D.C
2. Higley & Peterson Environmental Risk and Pest Management
http://ipmworld.umn.edu/chapters/higley.htm
3. Pesticide Industry Sales and Usage 1992-1993 Market Estimates, June 1994, Office of Prevention Pesticides and Toxic Substances, 33 pp
4. The Fredonia group, World Pesticides, Report No. 636 (The Fredonia Group, Cleveland, Ohio, 1994) as cited in AGRO, No. 225 (1995), page 16.
5. Information About Pesticides
http://www.broward.org/ppi02103.htm#GENERAL
6. Agriculture Chemical Inputs
http://www.wri.org/wr-98-99/agrichem.htm
7. Encyclopaedia Britannica CD
8. Educational web site
http://arneson.cornell.edu/pp444/NotesWWW/Biocntrl.htm
Steven Spencer
