In this article we will discuss about Pesticides:- 1. Properties of a Pesticide 2. Toxicity of Pesticide 3. Poisoning.
Properties of a Pesticide:
1. An ideal insecticide should control a particular pest and not kill other insects or animals.
2. It should degrade or leave the environment quickly and safely and not be accumulated in the environment.
3. It should have low toxicity for humans and other mammals.
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The way a pesticide affects the pest is important in choosing the correct pesticide.
On the basis of working principle, pesticides are categorized in following ways:
(A) Contact pesticides kill by touching the pest. These are used for soft-bodied insects like aphids; e.g., Phosphamidon, Endosulphan, Phenthion 20EC, methyl parathion, Endrin, Phosalone, etc.
(B) Stomach poisons must be eaten. They are used to control insects that chew foliage; e.g., Aldrin, Heptachlor, Chlorodane, BHC, etc.
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(C) Systematic pesticides are used in the field during cultivation along with the manures so that they can be taken into the sap of the plant. The pest then ingests the sap and get poisoned; e.g., Carbo- furan, Phoret, etc.
(D) Fumigants are gases that are sprayed over the field, which are inhaled or absorbed by the pest; e.g., Nethylamide, Calcium cyanide, Methyl bromide, Ethylene bromide, Ethylene dichloride, Carbon tetrachloride, etc.
(E) Protectants form a barrier on the plant. Fungicides protect the plant from germinating fungal spores.
Toxicity of Pesticide:
Pesticide toxicity is measured most often by LD50 and LC50. LD50 is the dose of a toxic substance required to kill 50% of a test population of animals. LD50 is the concentration of a toxic substance required to kill 50% of a test population of animals.
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LD50 is the abbreviation for “median lethal dose” and LC50 is the abbreviation of “median lethal concentration”. The lower the LD50of a pesticide, the more toxic is the substance. A high LD50 means that more of a substance is required to make a toxic dose.
Rotenone has an LD50 of 132. Malathion’s LD50 is 1,375, while table salt has an LD50 of 3,750. From this it can be said that rotenone, an organic pesticide, is much more toxic than malathion or salt. LDS0 only indicates the acute toxicity or immediate effect of a substance. Also of concern are the long-term effects, called chronic toxicity. This is of much greater concern to applicators handling chemicals on a daily basis.
In toxicity test, it is also possible to determine the highest doses or concentrations which cause no toxicity. These are — no observed effect dose (NOED) and no observed effect concentration (NOEC). These values can only be determined in situations where a higher dose or concentration has produced an effect like the same toxicity test of LC50 or LD50.
If a test is carried out where the end point is an adverse response other than death then an effective dose (ED50) or effective concentration (EC50) is determined. Here, the concentration or dose producing the effect in 50% of the population is determined.
Pesticide Poisoning:
Pesticide poisoning occurs from direct contact with the pesticide. This includes absorption through the skin, mouth, nose and eyes. Pesticides will soak into clothing and cause prolonged skin contact if the clothing, including leather or canvas shoes and gloves, are not removed immediately.
Symptoms of pesticide poisoning include headache, dizziness, dilated eyes, sweating, blurred vision, nausea, vomiting, cramps, diarrhoea, fatigue and weakness. If any of these symptoms appear, immediately contact physician or the poison control centre.