NCERT · Class 10 · Science · Our EnvironmentWhat is biological magnification (biomagnification)? Explain how harmful chemicals accumulate in various trophic levels of a food chain with a suitable example. Why are human beings most affected by it?

Introduction to Biological Magnification\nBiological magnification, also known as biomagnification, refers to the progressive increase in the concentration of toxic and non-biodegradable chemical substances (such as pesticides, heavy metals, and fertilizers) at successive trophic levels of a food chain.

Mechanism of Accumulation in a Food Chain

• Entry of Chemicals: Non-biodegradable chemicals like pesticides (e.g., DDT) are sprayed on crops to protect them from pests and diseases. These chemicals are washed down into the soil and water bodies by rain.
• Uptake by Producers: Aquatic plants and algae absorb these toxic chemicals along with water and minerals from the contaminated water body.
• Movement through Trophic Levels: When herbivores eat these plants, the chemicals enter their bodies. Since these chemicals cannot be metabolized or excreted by the organisms, they accumulate in their tissues.
• Magnification at Higher Levels: As carnivores eat herbivores, and top carnivores eat smaller carnivores, the concentration of the chemical multiplies manifold at each higher trophic level because a single carnivore consumes a large number of herbivores during its lifetime.

Example\nConsider an aquatic food chain:

1. Water: Contains $0.02 \text{ ppm}$ of pesticide (DDT).
2. Phytoplankton (Producers): Accumulates $5 \text{ ppm}$ due to continuous absorption.
3. Zooplankton (Primary Consumers): Accumulates $0.5 \text{ ppm}$.
4. Small Fish (Secondary Consumers): Accumulates $2 \text{ ppm}$.
5. Fish-eating Birds / Top Carnivores: Accumulates up to a massive $25 \text{ ppm}$ or more.

Why Human Beings are Most Affected\nHuman beings occupy the topmost position in many complex food chains (serving as omnivores or top carnivores). Due to biological magnification, the maximum concentration of harmful toxic chemicals accumulates in the bodies of organisms at the highest trophic level. Consequently, humans consume contaminated agricultural crops, fish, milk, and meat containing the highest levels of toxins, making them severely vulnerable to various chronic diseases, hormonal disorders, and neurological problems.