MP Board · Class 10 · Science · Our EnvironmentWhat is biological magnification (biomagnification)? Explain its causes and effects on living organisms with a suitable example. Why do top carnivores accumulate the maximum concentration of harmful chemicals?

Introduction to Biological Magnification\nBiological magnification, also known as biomagnification or biological amplification, refers to the progressive increase in the concentration of toxic, non-biodegradable chemicals (such as heavy metals and synthetic pesticides) at successive trophic levels of a food chain. As we move from producers to top carnivores, the concentration of these harmful substances multiplies manifold.

Causes of Biomagnification

1. Use of Non-Biodegradable Chemicals: Indiscriminate use of synthetic chemicals like pesticides (e.g., DDT) and heavy metals (e.g., mercury, lead, arsenic) in agriculture and industry.
2. Persistence in the Environment: These chemicals do not degrade naturally through biological or physical processes and remain active in the ecosystem for a very long period.
3. Trophic Transfer and Accumulation: When an organism consumes another organism, the non-biodegradable toxins present in the food are retained in the body tissues (fat and liver) and cannot be metabolized or excreted.

Detailed Example with Mechanism

• Consider a freshwater aquatic ecosystem where a small quantity of a pesticide like DDT is washed into a pond from nearby agricultural fields.
• Producers (Phytoplankton): The concentration of DDT in the water might be extremely low (e.g., 0.02 ppm), but phytoplanktons absorb and accumulate this toxin. Due to continuous consumption of water, the concentration in phytoplankton rises to 0.04 ppm.
• Primary Consumers (Zooplankton): When zooplankton feed on a large number of phytoplanktons, the DDT gets concentrated in their bodies (e.g., 0.23 ppm).
• Secondary Consumers (Small Fish): Small fish eat numerous zooplankton, further increasing the concentration of DDT (e.g., 2.07 ppm).
• Top Carnivores (Large Fish / Fish-eating Birds): At the top of the food chain, fish-eating birds or large fish consume many small fish. Consequently, the concentration of DDT multiplies drastically, reaching dangerous levels (e.g., up to 25 ppm or more).

Effects on Living Organisms

• Reproductive Failure: High concentration of chemicals like DDT interferes with calcium metabolism in birds, causing the thinning of eggshells. These eggs break prematurely during incubation, leading to a drastic decline in bird populations.
• Neurological and Physiological Damage: Toxic heavy metals like mercury and lead cause severe damage to the central nervous system, kidneys, liver, and overall metabolic functions in humans and animals.
• Disruption of Immune System: Accumulation of persistent organic pollutants weakens the immune system, making organisms highly susceptible to various diseases.