Increase in concentration of toxic substances at successive trophic levels due to their accumulations, it is called -

Answer

**Step-by-Step Solution:**

1. **Understanding the Concept**: The question asks about the increase in concentration of toxic substances at successive trophic levels. This phenomenon occurs when organisms at higher trophic levels consume organisms from lower levels that have accumulated toxins.

2. **Defining Trophic Levels**: Trophic levels refer to the different levels in a food chain, where each level represents a different stage of energy transfer. The primary producers (like plants) are at the first trophic level, herbivores at the second, and carnivores at the third and higher levels.

3. **Identifying the Process**: When toxic substances (like pesticides) enter the food chain, they are not easily broken down or excreted by organisms. As a result, these substances accumulate in the bodies of organisms.

4. **Explaining Biomagnification**: As you move up the trophic levels, the concentration of these toxic substances increases. This increase in concentration of toxins at each successive trophic level is known as biomagnification.

5. **Example of Biomagnification**: A common example is DDT (Dichloro-Diphenyl-Trichloroethane), a pesticide. When DDT enters aquatic ecosystems, it is absorbed by small fish. Larger fish that eat these smaller fish accumulate even more DDT in their bodies. This process continues up the food chain, leading to significantly higher concentrations of DDT in top predators.

6. **Conclusion**: Therefore, the correct term for the increase in concentration of toxic substances at successive trophic levels due to their accumulation is **biomagnification**.

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