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examBoard: Cambridge
examType: IGCSE
lessonTitle: Overuse of Insecticides and Herbicides
Modern farming relies heavily on chemicals to control pests and weeds. While these substances have helped increase food production, their overuse has led to serious environmental problems. This guide explores the impacts of using too many insecticides and herbicides in agriculture.
Key Definitions:
Insecticides target harmful insects that eat or damage crops. Common types include organophosphates, carbamates, pyrethroids and neonicotinoids. While they protect crops from pests, many insecticides also kill beneficial insects like bees and ladybirds that help with pollination and natural pest control.
Herbicides kill weeds that compete with crops for water, nutrients and sunlight. Popular herbicides include glyphosate (Roundup), atrazine and 2,4-D. These chemicals can drift beyond target areas, harming nearby wild plants that provide habitat for wildlife and contribute to ecosystem health.
When farmers use more pesticides than necessary or apply them incorrectly, these chemicals can cause widespread environmental damage. Let's explore the main impacts:
Pesticides don't just kill their target species – they affect many other organisms too. This disrupts ecosystems and reduces biodiversity in several ways:
Neonicotinoid insecticides are particularly harmful to bees and other pollinators. Studies show they damage bees' navigation abilities, reduce colony growth and weaken immune systems. With 75% of food crops depending on pollinators, this threatens both wild ecosystems and food production.
Birds, amphibians, fish and mammals can be poisoned by pesticides through direct contact, eating contaminated food, or drinking polluted water. For example, studies have linked pesticide use to declining bird populations in agricultural areas across Europe.
Natural predators like ladybirds, lacewings and parasitic wasps help control pest populations naturally. When these beneficial insects are killed by broad-spectrum insecticides, pest populations can actually increase in the long run – creating dependence on more chemicals.
Pesticides often don't stay where they're applied. Rain washes them into streams, rivers, lakes and eventually the ocean, causing widespread water pollution:
Once in water systems, pesticides can:
Atrazine, a common herbicide used on corn crops, is one of the most frequently detected pesticides in water supplies. Studies have shown it can disrupt hormones in frogs, causing males to develop female characteristics at concentrations as low as 0.1 parts per billion. In the US, atrazine has been found in approximately 75% of stream water and 40% of groundwater samples tested in agricultural areas.
Some pesticides don't break down easily in the environment. Instead, they build up in the bodies of living organisms and become more concentrated as they move up the food chain.
This occurs when an organism absorbs a substance faster than it can get rid of it. For example, fish in contaminated water absorb pesticides through their gills and by eating contaminated food. Over time, the chemical builds up in their fatty tissues to levels much higher than in the surrounding water.
This happens when predators eat contaminated prey, concentrating the chemicals further up the food chain. A small fish might contain low levels of a pesticide, but a bird that eats many of these fish will accumulate much higher concentrations. Top predators like eagles, polar bears and humans can end up with dangerous levels of these chemicals in their bodies.
Healthy soil is a complex ecosystem teeming with life. Overuse of pesticides damages this underground world:
Perhaps the most ironic impact of pesticide overuse is that it eventually makes these chemicals less effective. This happens through a process called pesticide resistance:
Today, over 580 insect species, 230 weed species and numerous plant pathogens have developed resistance to pesticides. This leads farmers to use increasingly toxic chemicals or higher doses, worsening environmental impacts.
One of the most famous examples of pesticide damage involved DDT, an insecticide widely used in the mid-20th century. DDT accumulated in the food chain and caused eggshell thinning in birds of prey like peregrine falcons and bald eagles. Their populations crashed as eggs broke before hatching. After DDT was banned in many countries in the 1970s, these bird populations gradually recovered. This case demonstrated how chemicals can have unexpected effects far beyond their intended targets and led to stricter testing requirements for new pesticides.
Fortunately, farmers don't have to choose between crop protection and environmental health. Many sustainable alternatives can reduce reliance on chemical pesticides:
Using natural predators and parasites to control pests. For example, releasing ladybirds to eat aphids or using Bacillus thuringiensis (Bt), a naturally occurring soil bacterium, to control caterpillars.
Changing which crops are grown in a field each season disrupts pest life cycles and reduces weed problems. This ancient practice helps break pest cycles naturally.
A holistic approach that combines multiple strategies and uses chemicals only as a last resort. IPM focuses on prevention, monitoring and control methods that minimise risks to people and the environment.
The challenge for modern agriculture is to produce enough food while protecting the environment. This requires:
By understanding the environmental impacts of pesticide overuse, we can make more informed decisions about how we grow and choose our food. The health of our ecosystems depends on finding this balance.
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