Which of the following statements is not correct regarding biomagnification ?
(i) Mercury accumulated by an organism cannot be metabolised.
(ii) In the process of biomagnification, concentration of DDT is increased at successive trophic levels.
(iii) Accumulation of cadmimu can cause thinning of egg shell in birds.
(iv) DDT accumulation is a major cause of reduced population of fish eating birds.
(v) Biomagnification occurs only in aquatic food chain.

Options

A. (i), (iii) and (v)
B. (iii) and (iv)
C. (iii) and (v)
D. (i), (ii) and (iv)

Explanation

To solve the question regarding which statement is not correct about biomagnification, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Understanding Biomagnification**:
- Biomagnification refers to the increasing concentration of toxic substances, such as heavy metals and pesticides, in the tissues of organisms at each successive trophic level in a food chain.

2. **Analyzing Statement (i)**:
- "Mercury accumulated by an organism cannot be metabolised."
- This statement is correct. Mercury is a heavy metal that cannot be easily metabolized by organisms, leading to its accumulation.

3. **Analyzing Statement (ii)**:
- "In the process of biomagnification, concentration of DDT is increased at successive trophic levels."
- This statement is also correct. DDT, a pesticide, accumulates and increases in concentration as it moves up the food chain.

4. **Analyzing Statement (iii)**:
- "Accumulation of cadmium can cause thinning of egg shell in birds."
- This statement is incorrect. The thinning of eggshells in birds is primarily associated with the accumulation of DDT, not cadmium. Cadmium does have toxic effects but is not directly linked to eggshell thinning.

5. **Analyzing Statement (iv)**:
- "DDT accumulation is a major cause of reduced population of fish-eating birds."
- This statement is correct. The thinning of eggshells due to DDT leads to decreased reproductive success in these birds.

6. **Analyzing Statement (v)**:
- "Biomagnification occurs only in aquatic food chain."
- This statement is incorrect. Biomagnification can occur in both aquatic and terrestrial food chains.

7. **Conclusion**:
- The statements that are not correct are (iii) and (v). However, since the question asks for which statement is not correct regarding biomagnification, the most relevant incorrect statement is (iii) because it misattributes the cause of eggshell thinning.

### Final Answer:
The statement that is not correct regarding biomagnification is (iii) "Accumulation of cadmium can cause thinning of egg shell in birds."