Pesticides – It’s benefits and Bad Effects

A pest, broadly defined, is any organism – plant, animal, or micro-organism that is distractive or living where it is unwanted. And a pesticide is called any substance or mixture of substances intended for destroying, preventing, repelling, or mitigating any pest such as insects, mites, nematodes, weeds, rats, etc., including insecticide, herbicide, fungicide, rodenticides, fumigants, and various other substances used to control or mitigate pests. At present, there are near about 15,000 different types of pesticides in the world.

History of pesticide

The history of pesticides can be divided into three phases:

1. The First phase, the period before the 1870s: At that period natural substances were used as pesticides, such as in ancient Greece sulfur was used to control pests;
2. The second phase, between 1870s-1945: At that period both natural and inorganic synthetic substances were used as pesticides.
3. The third phase, since 1945: is the era of organic synthetic Compound that being used as pesticides.

In this phase, the human-made organic compounds are being used as pesticides, e.g., DDT, 2, 4-D, and later HCH, dieldrin, etc. Human synthesized most pesticides, and they were named chemical pesticides. The application of chemical pesticides has been a significant mark of human civilization, which significantly protects the drops from pests and increases agricultural productivity.

Classification of pesticides

1. By target: Insecticides, Herbicides, fungicides, rodenticides, algaecides, and nematicides, etc.
2. By chemical nature: A. Organic B. Inorganic

3. By physical state: – Dusts, dissolved solution, suspended solution, volatile solids
4. By mode of action: – contact poisons, fumigants, stomach poisons, systemic poisons.• Insecticides – act pesticidally against the growth or survival of insects. Also includes specific types such as miticides, mosquito larvicides or adulticides;

• Herbicides – act pesticidally against plants, weeds, or grasses;
• Rodenticides – act pesticidally against rats or other rodents;
• Avicides – act pesticidally against damaging bird populations;
• Fungicides – act pesticidally against fungi on food or grain crops;
• Nematicides – act pesticidally against nematodes;
• Fumigants – gaseous pesticides used for invertebrate and fungal control;
• Antimicrobials – act pesticidally against microscopic organisms on a variety of sites;
• Plant Growth Regulators – accelerate or retard plant growth rates;
• Insect Growth Regulators – retard insect growth;
• Biopesticides – naturally occurring substances with pesticidal properties, including microbial pesticides, biochemical pesticides and plant incorporated protectants;
• Piscicides – act pesticidally against unwanted or invasive fish populations; and
• Molluscides – act pesticidally against slugs, snails, or bivalves.

Insecticides

Insecticides are those compounds that are effective against insects. Many insecticides have been developed and used to control various species of insects. While most insecticides are applied as spays, other are dusts, aerosols, fumigants and baits.

The majority of insecticides used today are synthetic organic chemicals and most of them are nerve poisons. They act by inhibiting the organism’s enzymes or interacting with other target sites vital to the proper functioning of the insect`s nervous system. Although there are many synthetic organic insecticides, three main groups are:

1. chlorinated hydrocarbons
2. organophosphorus compounds or organophosphates and
3. Carbamates.

1. Chlorinated hydrocarbons:

chlorinated hydrocarbons, also called organochlorines, were the first commercial organic insecticides to be developed. DDT, Aldrin, chlordane, dieldrin, endrin, lindane, and heptachlor are some examples.

2. Organophosphorus Compounds:

These compounds are the most toxic among the insecticides; they are dangerous both for insects and mammals, such as parathion, Paraoxon, timet and tetram. And these are super toxic category poisons for human.

Only little as 2 mg of parathion has able to kill a child. Symptoms of poisoning in humans include vomiting, diarrhea, cramp’s sweating, salivation, blurred vision and muscular tremors. Severe cases may be fatal due to respiratory failure.

3. Carbamates:

In the same way that organophosphate insecticides such as parathion and malathion are derivatives of phosphoric acid, the carbamates are derivatives of carbamic acid (HO-CO-NH2). Carbamates are widely used for worm control on vegetables. Examples of carbamates include aldicarb and carbofuran.

Herbicides or Weedicides

In Vietnam War, the U.S Air Force’s defoliation program first applied a massive quantity of pure 2,4-D (2,4-Dichlorophenoxy acetic acid) and 2,4,5-T (2,4,5 Trichloro phenoxy acetic acid) on Vietnam’s agricultural and forest land between 1965 and 1970. In addition to military use in Vietnam, Phenoxy herbicides (PHs) are widely used in the U.S for controlling weeds in agriculture, lakes, ponds, and forests.

The biochemical actions of Phenoxy herbicides (PHs) in plants are complex. After application, the chemicals are absorbed primarily through stomata. Secondly, these absorb by root hair with water by the sensitive plants disrupt growth and various metabolic processes as they are translocated through vascular tissue.

Clinical symptoms of severely poisoned farmers include pain and weakness in the lower extremities, slowed nerve conduction velocity, and muscle spasms. Specific neurotoxic effects of 2, 4,-D have recently been examined in response to reports of an episodic increase in intracranial skull pressure associated with insecticides intoxication.

PHs were banned for forestry in 1979 due to a combination of public pressure and US Environmental Protection Agency (EPA) results after the Alsea II report. PHs are still widely used as herbicides for corn, wheat, and rice crops.

The annual world production of pesticides grew from 6000 million pounds (1954) to over 24000 million pounds (1973). Of these, about 600 million pounds were Organochlorine insecticides that persist in the environment.

Bad effect of pesticides

• When we apply a pesticide to crops, plants and animals absorb most of it. But a portion of the pesticide is vaporized in the atmosphere and deposited in rainwater.
• Another portion of it remains in the soil. It also gets mixed up with the surface water that runs off to rivers and lakes. Still, some of it reaches groundwater via leaching by rain.
• Rain can carry pesticides for away. Once, the water of a lake in Japan was found to be contaminated by a pesticide. Japan, at the time, did not use any pesticides. It then found that the pesticide used in China and Korea about 1500 km away from the lake caused rainfall contamination.
• Fog in thicker than rain, so that that fog can contain more pesticides than rain. In cold countries, therefore, pesticide contamination by condensation is a severe environmental problem.

Benefits and risks of pesticide application

• There are about 9,000 species of insects and mites, 50,000 species of plant pathogens, and 8,000 weeds damage crops in the world.
• Insect pests approximately losses 14% of crops; plant pathogens losses 13%, and weeds a 13% loss.
• About 35% more agricultural products are produced by using pesticides.
• If pesticides are not used, the loss of fruits, vegetables, and cereals will injury by pest reach 78%, 54%, and 32%, respectively. And Crop loss by pests declines to 35% – 42%.
• Because of the world’s limited croplands and growing population, it is necessary to take all measures to increase crop production to ensure food safety.
• Most pesticides are not spontaneously generated. Most of them are highly toxic to both humans and the environment
• Pesticides and their degraded products would flow into the Rivers, Lakes, and water body and mix with soils and the atmosphere, resulting in the accumulation of toxic substances and threatening human health and the environment.
• By using pesticides, the environmental pollution in Asia, Africa, Latin America, the Middle East, and Eastern Europe is now serious.

There are four aspects of issues in pesticide production and application worldwide:

1. Some countries still produced or/and used highly toxic pesticides;
2. Pesticides are overused to cotton, vegetables and rice;
3. Some countries are not capable to effectively regulate pesticides qualities and thus result in the
   production and consumption of poor and unqualified pesticides,
4. Pesticide residue standards do not execute effectively.

Dirty dozen:

In 1995, the Governing Council of UN Environment Programme (UNEP) decided to research and examine the toxicity and its impacts on humans and the environment of 12 Persistent Organic Pollutants-POPs.

These 12 harmful pollutants that ate selected to examine are called a whole the Dirty Dozen. The name of dirty dozen are given below:

1. Aldrin
2. chlordane
3. DDT
4. Dieldrin
5. Endrin
6. Heptachlor
7. Hexachlorobenzene
8. Mirex
9. polychlorinated biphenyls
10. polychlorinated dibenzo-p-dioxins
11. polychlorinated dibenzofurans, and
12. toxaphene.

Delegates from different countries met at Geneva during September 1999 to discuss to control these 12 harmful, persistent organic pollutants-POPs.

They decided to ben on the use of 4, out of 10 harmful POPs those are chlordane, Dieldrin, Heptachlor, and Mirex.

In 2001, the UN Stockholm Convention on Persistent Organic Pollutants was held.

At that convention, it was ben or restriction on production and application of all POPs harmful to human and environment and signed a treaty of 170 countries on it. This treaty was excited in 2004.

Worldwide Situation of Pesticide Pollution

• More than 4.5 million tons of chemical pesticides are yearly sprayed into the environment worldwide.
• Currently, in the world, nearly 500 different types of pesticides are mass uses, of which organochlorines pesticides, some herbicides, and pesticides containing mercury, arsenic, and lead are highly poisonous to the environment.
• Of used pesticides, only 1-2% of the sprayed pesticides are effective for targets, and 89-99% release to non-target soils, water bodies, and atmosphere, and finally absorbed by almost every organism.
• According to a report from the United States EPA, many of the nation’s rural wells contain at least one of 127 pesticides.
• A research panel of Indiana University analyzed barks from 90 sites from the equator to high latitude cold regions and detected DDT, aldrin, and lindane residuals.
• High-residual pesticides like DDT have been detected in the Greenland ice sheet and Antarctic penguins’ bodies, which resulted from atmospheric circulation, ocean currents, and biological enrichment of pesticides.
• According to a WHO and UNEP report, there are more than 26 million human pesticide poisonings with about 220,000 deaths per year.

Reference:
1. GreenPage
2. Book: Environmental Toxicology (Second Edition) -By Ming-Hu Yu
3. WIKIPEDIA