Pesticides

Pesticides are chemical or biological substances used to prevent, control, or eliminate pests that harm crops, animals, or human health. Pests may include insects, weeds, fungi, rodents, nematodes, or other organisms that interfere with agricultural productivity or the storage and quality of food. Pesticides play a critical role in modern agriculture by enhancing crop yields and protecting food supplies; however, their widespread use has also raised significant concerns about environmental pollution, ecological imbalance, and public health.

Definition and Classification

A pesticide is any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating pests. Pesticides are classified according to their target organisms, chemical composition, or mode of action.
Based on target organisms:

• Insecticides: Control insects (e.g., DDT, malathion).
• Herbicides: Destroy unwanted weeds or plants (e.g., glyphosate, atrazine).
• Fungicides: Eliminate fungi and moulds affecting crops (e.g., mancozeb, carbendazim).
• Rodenticides: Kill rats and other rodents (e.g., zinc phosphide, warfarin).
• Nematicides: Control nematodes that attack plant roots (e.g., aldicarb).
• Bactericides: Used against harmful bacteria (e.g., copper sulphate).
• Acaricides: Target mites and ticks (e.g., dicofol).

Based on chemical composition:

• Organochlorines: Stable compounds such as DDT and aldrin, known for long persistence in the environment.
• Organophosphates: More degradable but highly toxic, e.g., parathion, chlorpyrifos.
• Carbamates: Moderate persistence, including carbaryl and aldicarb.
• Pyrethroids: Synthetic analogues of natural pyrethrins, e.g., cypermethrin.
• Biopesticides: Derived from natural organisms like bacteria or fungi (e.g., Bacillus thuringiensis).
• Neonicotinoids: Affect the nervous system of insects, e.g., imidacloprid.

History and Development

The use of pest control substances dates back to ancient civilisations. The Sumerians used sulphur compounds, and the Chinese employed arsenic and plant extracts over 3,000 years ago. The modern pesticide era began in the mid-20th century with the discovery of DDT (dichlorodiphenyltrichloroethane) during the Second World War, which revolutionised pest control and disease management.
However, by the 1960s, evidence of pesticide-related environmental harm emerged, notably highlighted by Rachel Carson’s book Silent Spring (1962), which documented the ecological consequences of indiscriminate DDT use. This led to stricter regulations and a global shift towards safer and more sustainable pest management approaches.

Mechanism of Action

Pesticides function by interfering with essential biological processes of target organisms. The mechanism varies depending on the pesticide type:

• Neurotoxic pesticides disrupt the nervous system, causing paralysis or death (e.g., organophosphates).
• Respiratory inhibitors block energy production in cells.
• Growth regulators interfere with reproduction or development (used in insect control).
• Cell membrane disruptors affect plant cell integrity (common in herbicides).
• Enzyme inhibitors prevent normal metabolic activities within pests.

Benefits and Importance

Pesticides provide several economic and social benefits, particularly in agriculture and public health:

• Crop protection: Prevent losses caused by pests, diseases, and weeds, which can otherwise destroy up to 40% of global crop yields.
• Food preservation: Extend the storage life of grains and perishable products.
• Public health protection: Control disease vectors such as mosquitoes (malaria, dengue) and fleas (plague).
• Livestock protection: Prevent infestations that reduce animal productivity.
• Economic efficiency: Reduce production costs and increase farmer income through higher yields.

Environmental and Health Impacts

Despite their benefits, pesticides pose several environmental and health hazards when misused or overapplied.
Environmental effects:

• Soil contamination: Residues persist and alter microbial balance, affecting fertility.
• Water pollution: Run-off and leaching contaminate groundwater and aquatic ecosystems.
• Bioaccumulation and biomagnification: Persistent pesticides like DDT accumulate in food chains, harming predators such as birds and fish.
• Loss of biodiversity: Non-target species, including pollinators like bees, are adversely affected.
• Development of resistant pest strains: Repeated exposure leads to genetic adaptation among pest populations.

Health effects on humans:

• Acute poisoning: Symptoms include dizziness, nausea, headaches, and respiratory distress. Severe exposure can lead to convulsions, coma, or death.
• Chronic effects: Long-term exposure has been linked to cancers, reproductive disorders, neurological impairment, and endocrine disruption.
• Occupational risks: Farmers, pesticide applicators, and industrial workers face higher exposure levels.
• Residues in food: Improper pesticide use leaves harmful residues that enter the human food chain.

Regulation and Control

Governments worldwide have established regulations to manage pesticide use, manufacturing, and disposal. In India, pesticide regulation is governed by the Insecticides Act, 1968, and the Insecticides Rules, 1971, administered by the Central Insecticides Board and Registration Committee (CIBRC) under the Ministry of Agriculture and Farmers’ Welfare.
Key measures include:

• Registration and approval of pesticide formulations.
• Labelling standards specifying toxicity levels and safe handling instructions.
• Regular monitoring of pesticide residues in food products.
• Restrictions or bans on hazardous chemicals (e.g., DDT, endosulfan).
• Promotion of safer alternatives through Integrated Pest Management (IPM) and organic farming.

Alternatives and Sustainable Practices

With growing environmental awareness, emphasis is shifting towards sustainable pest management strategies that minimise chemical dependency. Major alternatives include:

• Integrated Pest Management (IPM): Combines biological, cultural, and mechanical control with limited pesticide use.
• Biopesticides: Use of microorganisms (e.g., Bacillus thuringiensis) and natural extracts for pest control.
• Botanical pesticides: Derived from plants such as neem (Azadirachta indica), which have insect-repelling properties.
• Genetically modified (GM) crops: Engineered to resist specific pests, reducing the need for chemical pesticides.
• Precision agriculture: Employs sensors and data analysis to apply minimal and targeted pesticide doses.

Safe Handling and Disposal

Proper storage, handling, and disposal of pesticides are vital to reduce exposure risks:

• Use protective clothing, gloves, and masks during application.
• Avoid spraying in windy conditions to prevent drift.
• Store pesticides in labelled, sealed containers away from food and children.
• Dispose of empty containers safely according to local environmental regulations.

Training and awareness among farmers are essential for promoting safe pesticide practices and preventing accidental poisoning or environmental contamination.